diff --git a/beacon_chain/beacon_node.nim b/beacon_chain/beacon_node.nim
index 8c9b5ab7f..f856e74c8 100644
--- a/beacon_chain/beacon_node.nim
+++ b/beacon_chain/beacon_node.nim
@@ -1277,13 +1277,17 @@ when hasPrompt:
 
       when compiles(defaultChroniclesStream.output.writer):
         defaultChroniclesStream.output.writer =
-          proc (logLevel: LogLevel, msg: LogOutputStr) {.gcsafe.} =
-            # p.hidePrompt
-            erase statusBar
-            # p.writeLine msg
-            stdout.write msg
-            render statusBar
-            # p.showPrompt
+          proc (logLevel: LogLevel, msg: LogOutputStr) {.gcsafe, raises: [Defect].} =
+            try:
+              # p.hidePrompt
+              erase statusBar
+              # p.writeLine msg
+              stdout.write msg
+              render statusBar
+              # p.showPrompt
+            except Exception as e: # render raises Exception
+              if e is Defect: raise (ref Defect)(e)
+              discard # Status bar not critical
 
       proc statusBarUpdatesPollingLoop() {.async.} =
         while true:
@@ -1302,8 +1306,11 @@ when isMainModule:
 
   when compiles(defaultChroniclesStream.output.writer):
     defaultChroniclesStream.output.writer =
-      proc (logLevel: LogLevel, msg: LogOutputStr) {.gcsafe.} =
-        stdout.write(msg)
+      proc (logLevel: LogLevel, msg: LogOutputStr) {.gcsafe, raises: [Defect].} =
+        try:
+          stdout.write(msg)
+        except IOError:
+          discard # nothing to do..
 
   randomize()
 
diff --git a/beacon_chain/beacon_node_types.nim b/beacon_chain/beacon_node_types.nim
index 2b4d3f285..9b94f6e14 100644
--- a/beacon_chain/beacon_node_types.nim
+++ b/beacon_chain/beacon_node_types.nim
@@ -1,3 +1,5 @@
+{.push raises: [Defect].}
+
 import
   deques, tables, options,
   stew/[endians2, byteutils], chronicles,
diff --git a/beacon_chain/conf.nim b/beacon_chain/conf.nim
index 5ef9a3ed1..16c689659 100644
--- a/beacon_chain/conf.nim
+++ b/beacon_chain/conf.nim
@@ -1,3 +1,5 @@
+{.push raises: [Defect].}
+
 import
   os, options, strformat, strutils,
   chronicles, confutils, json_serialization,
@@ -278,7 +280,10 @@ proc defaultDataDir*(conf: BeaconNodeConf): string =
 
 proc validatorFileBaseName*(validatorIdx: int): string =
   # there can apparently be tops 4M validators so we use 7 digits..
-  fmt"v{validatorIdx:07}"
+  try:
+    fmt"v{validatorIdx:07}"
+  except ValueError as e:
+    raiseAssert e.msg
 
 func dumpDir*(conf: BeaconNodeConf): string =
   conf.dataDir / "dump"
@@ -292,10 +297,10 @@ func databaseDir*(conf: BeaconNodeConf): string =
 func defaultListenAddress*(conf: BeaconNodeConf): IpAddress =
   # TODO: How should we select between IPv4 and IPv6
   # Maybe there should be a config option for this.
-  parseIpAddress("0.0.0.0")
+  return static: parseIpAddress("0.0.0.0")
 
 func defaultAdminListenAddress*(conf: BeaconNodeConf): IpAddress =
-  parseIpAddress("127.0.0.1")
+  return static: parseIpAddress("127.0.0.1")
 
 iterator validatorKeys*(conf: BeaconNodeConf): ValidatorPrivKey =
   for validatorKeyFile in conf.validators:
@@ -305,13 +310,17 @@ iterator validatorKeys*(conf: BeaconNodeConf): ValidatorPrivKey =
       warn "Failed to load validator private key",
         file = validatorKeyFile.string, err = err.msg
 
-  for kind, file in walkDir(conf.localValidatorsDir):
-    if kind in {pcFile, pcLinkToFile} and
-        cmpIgnoreCase(".privkey", splitFile(file).ext) == 0:
-      try:
-        yield ValidatorPrivKey.init(readFile(file).string)
-      except CatchableError as err:
-        warn "Failed to load a validator private key", file, err = err.msg
+  try:
+    for kind, file in walkDir(conf.localValidatorsDir):
+      if kind in {pcFile, pcLinkToFile} and
+          cmpIgnoreCase(".privkey", splitFile(file).ext) == 0:
+        try:
+          yield ValidatorPrivKey.init(readFile(file).string)
+        except CatchableError as err:
+          warn "Failed to load a validator private key", file, err = err.msg
+  except OSError as err:
+    warn "Cannot load validator keys",
+      dir = conf.localValidatorsDir, err = err.msg
 
 template writeValue*(writer: var JsonWriter,
                      value: TypedInputFile|InputFile|InputDir|OutPath|OutDir|OutFile) =
diff --git a/beacon_chain/extras.nim b/beacon_chain/extras.nim
index 30489f8a5..1b6367ab7 100644
--- a/beacon_chain/extras.nim
+++ b/beacon_chain/extras.nim
@@ -5,6 +5,8 @@
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
+{.push raises: [Defect].}
+
 # Temporary dumping ground for extra types and helpers that could make it into
 # the spec potentially
 #
diff --git a/beacon_chain/interop.nim b/beacon_chain/interop.nim
index 35eea80f3..6aed238d9 100644
--- a/beacon_chain/interop.nim
+++ b/beacon_chain/interop.nim
@@ -1,3 +1,5 @@
+{.push raises: [Defect].}
+
 import
   stew/endians2, stint,
   ./extras, ./ssz,
@@ -14,7 +16,7 @@ func get_eth1data_stub*(deposit_count: uint64, current_epoch: Epoch): Eth1Data =
     block_hash: hash_tree_root(hash_tree_root(voting_period).data),
   )
 
-func makeInteropPrivKey*(i: int): ValidatorPrivKey =
+func makeInteropPrivKey*(i: int): BlsResult[ValidatorPrivKey] =
   var bytes: array[32, byte]
   bytes[0..7] = uint64(i).toBytesLE()
 
@@ -26,7 +28,7 @@ func makeInteropPrivKey*(i: int): ValidatorPrivKey =
     privkeyBytes = eth2hash(bytes)
     key = (UInt256.fromBytesLE(privkeyBytes.data) mod curveOrder).toBytesBE()
 
-  ValidatorPrivKey.fromRaw(key).tryGet()
+  ValidatorPrivKey.fromRaw(key)
 
 const eth1BlockHash* = block:
   var x: Eth2Digest
diff --git a/beacon_chain/merkle_minimal.nim b/beacon_chain/merkle_minimal.nim
index 9ff7e938b..b4fa6eb3f 100644
--- a/beacon_chain/merkle_minimal.nim
+++ b/beacon_chain/merkle_minimal.nim
@@ -10,6 +10,8 @@
 # Merkle tree helpers
 # ---------------------------------------------------------------
 
+{.push raises: [Defect].}
+
 import
   sequtils, strutils, macros, bitops,
   # Specs
diff --git a/beacon_chain/spec/beaconstate.nim b/beacon_chain/spec/beaconstate.nim
index 29b8040af..972470303 100644
--- a/beacon_chain/spec/beaconstate.nim
+++ b/beacon_chain/spec/beaconstate.nim
@@ -5,6 +5,8 @@
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
+{.push raises: [Defect].}
+
 import
   tables, algorithm, math, sequtils, options,
   json_serialization/std/sets, chronicles, stew/bitseqs,
diff --git a/beacon_chain/spec/datatypes.nim b/beacon_chain/spec/datatypes.nim
index 08107ca89..832f74fe9 100644
--- a/beacon_chain/spec/datatypes.nim
+++ b/beacon_chain/spec/datatypes.nim
@@ -17,6 +17,9 @@
 # `ref` - this can be achieved by wrapping them in higher-level
 # types / composition
 
+# TODO report compiler crash when this is uncommented
+# {.push raises: [Defect].}
+
 import
   macros, hashes, json, strutils, tables,
   stew/[byteutils, bitseqs], chronicles,
diff --git a/beacon_chain/spec/helpers.nim b/beacon_chain/spec/helpers.nim
index 0864331f2..c1d6a4e03 100644
--- a/beacon_chain/spec/helpers.nim
+++ b/beacon_chain/spec/helpers.nim
@@ -7,6 +7,8 @@
 
 # Uncategorized helper functions from the spec
 
+{.push raises: [Defect].}
+
 import
   # Standard lib
   math,
diff --git a/beacon_chain/spec/network.nim b/beacon_chain/spec/network.nim
index dbfbb87ad..2f62d6edb 100644
--- a/beacon_chain/spec/network.nim
+++ b/beacon_chain/spec/network.nim
@@ -5,6 +5,8 @@
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
+{.push raises: [Defect].}
+
 import
   strformat,
   stew/byteutils,
@@ -27,22 +29,39 @@ const
   defaultEth2RpcPort* = 9090
 
 func getBeaconBlocksTopic*(forkDigest: ForkDigest): string =
-  &"/eth2/{toHex forkDigest}/{topicBeaconBlocksSuffix}"
+  try:
+    &"/eth2/{toHex forkDigest}/{topicBeaconBlocksSuffix}"
+  except ValueError as e:
+    raiseAssert e.msg
 
 func getVoluntaryExitsTopic*(forkDigest: ForkDigest): string =
-  &"/eth2/{toHex forkDigest}/{topicVoluntaryExitsSuffix}"
+  try:
+    &"/eth2/{toHex forkDigest}/{topicVoluntaryExitsSuffix}"
+  except ValueError as e:
+    raiseAssert e.msg
 
 func getProposerSlashingsTopic*(forkDigest: ForkDigest): string =
-  &"/eth2/{toHex forkDigest}/{topicProposerSlashingsSuffix}"
+  try:
+    &"/eth2/{toHex forkDigest}/{topicProposerSlashingsSuffix}"
+  except ValueError as e:
+    raiseAssert e.msg
 
 func getAttesterSlashingsTopic*(forkDigest: ForkDigest): string =
-  &"/eth2/{toHex forkDigest}/{topicAttesterSlashingsSuffix}"
+  try:
+    &"/eth2/{toHex forkDigest}/{topicAttesterSlashingsSuffix}"
+  except ValueError as e:
+    raiseAssert e.msg
 
 func getAggregateAndProofsTopic*(forkDigest: ForkDigest): string =
-  &"/eth2/{toHex forkDigest}/{topicAggregateAndProofsSuffix}"
+  try:
+    &"/eth2/{toHex forkDigest}/{topicAggregateAndProofsSuffix}"
+  except ValueError as e:
+    raiseAssert e.msg
 
 func getAttestationTopic*(forkDigest: ForkDigest, committeeIndex: uint64): string =
   # https://github.com/ethereum/eth2.0-specs/blob/v0.11.0/specs/phase0/validator.md#broadcast-attestation
-  let topicIndex = committeeIndex mod ATTESTATION_SUBNET_COUNT
-  &"/eth2/{toHex forkDigest}/committee_index{topicIndex}{topicAttestationsSuffix}"
-
+  try:
+    let topicIndex = committeeIndex mod ATTESTATION_SUBNET_COUNT
+    &"/eth2/{toHex forkDigest}/committee_index{topicIndex}{topicAttestationsSuffix}"
+  except ValueError as e:
+    raiseAssert e.msg
diff --git a/beacon_chain/spec/state_transition_block.nim b/beacon_chain/spec/state_transition_block.nim
index f9396d945..60838ffd8 100644
--- a/beacon_chain/spec/state_transition_block.nim
+++ b/beacon_chain/spec/state_transition_block.nim
@@ -32,6 +32,8 @@
 # improvements to be made - other than that, keep things similar to spec for
 # now.
 
+{.push raises: [Defect].}
+
 import
   algorithm, collections/sets, chronicles, options, sequtils, sets,
   ../extras, ../ssz, metrics,
@@ -400,16 +402,19 @@ proc process_block*(
   # https://github.com/ethereum/eth2.0-metrics/blob/master/metrics.md#additional-metrics
   # doesn't seem to specify at what point in block processing this metric is to be read,
   # and this avoids the early-return issue (could also use defer, etc).
-  beacon_pending_deposits.set(
-    state.eth1_data.deposit_count.int64 - state.eth1_deposit_index.int64)
-  beacon_processed_deposits_total.set(state.eth1_deposit_index.int64)
+  try:
+    beacon_pending_deposits.set(
+      state.eth1_data.deposit_count.int64 - state.eth1_deposit_index.int64)
+    beacon_processed_deposits_total.set(state.eth1_deposit_index.int64)
 
-  # Adds nontrivial additional computation, but only does so when metrics
-  # enabled.
-  beacon_current_live_validators.set(toHashSet(
-    mapIt(state.current_epoch_attestations, it.proposerIndex)).len.int64)
-  beacon_previous_live_validators.set(toHashSet(
-    mapIt(state.previous_epoch_attestations, it.proposerIndex)).len.int64)
+    # Adds nontrivial additional computation, but only does so when metrics
+    # enabled.
+    beacon_current_live_validators.set(toHashSet(
+      mapIt(state.current_epoch_attestations, it.proposerIndex)).len.int64)
+    beacon_previous_live_validators.set(toHashSet(
+      mapIt(state.previous_epoch_attestations, it.proposerIndex)).len.int64)
+  except Exception as e: # TODO https://github.com/status-im/nim-metrics/pull/22
+    trace "Couldn't update metrics", msg = e.msg
 
   if not process_block_header(state, blck, flags, stateCache):
     notice "Block header not valid", slot = shortLog(state.slot)
diff --git a/beacon_chain/spec/state_transition_epoch.nim b/beacon_chain/spec/state_transition_epoch.nim
index 7f8426277..d1490f6ae 100644
--- a/beacon_chain/spec/state_transition_epoch.nim
+++ b/beacon_chain/spec/state_transition_epoch.nim
@@ -32,6 +32,8 @@
 # improvements to be made - other than that, keep things similar to spec for
 # now.
 
+{.push raises: [Defect].}
+
 import
   math, options, sequtils, tables,
   stew/[bitseqs, bitops2], chronicles, json_serialization/std/sets,
@@ -449,13 +451,16 @@ proc process_epoch*(state: var BeaconState) {.nbench.}=
   process_final_updates(state)
 
   # Once per epoch metrics
-  beacon_finalized_epoch.set(state.finalized_checkpoint.epoch.int64)
-  beacon_finalized_root.set(state.finalized_checkpoint.root.toGaugeValue)
-  beacon_current_justified_epoch.set(
-    state.current_justified_checkpoint.epoch.int64)
-  beacon_current_justified_root.set(
-    state.current_justified_checkpoint.root.toGaugeValue)
-  beacon_previous_justified_epoch.set(
-    state.previous_justified_checkpoint.epoch.int64)
-  beacon_previous_justified_root.set(
-    state.previous_justified_checkpoint.root.toGaugeValue)
+  try:
+    beacon_finalized_epoch.set(state.finalized_checkpoint.epoch.int64)
+    beacon_finalized_root.set(state.finalized_checkpoint.root.toGaugeValue)
+    beacon_current_justified_epoch.set(
+      state.current_justified_checkpoint.epoch.int64)
+    beacon_current_justified_root.set(
+      state.current_justified_checkpoint.root.toGaugeValue)
+    beacon_previous_justified_epoch.set(
+      state.previous_justified_checkpoint.epoch.int64)
+    beacon_previous_justified_root.set(
+      state.previous_justified_checkpoint.root.toGaugeValue)
+  except Exception as e: # TODO https://github.com/status-im/nim-metrics/pull/22
+    trace "Couldn't update metrics", msg = e.msg
diff --git a/beacon_chain/spec/state_transition_helpers.nim b/beacon_chain/spec/state_transition_helpers.nim
index f6eb6c668..3e6aee73b 100644
--- a/beacon_chain/spec/state_transition_helpers.nim
+++ b/beacon_chain/spec/state_transition_helpers.nim
@@ -5,6 +5,8 @@
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
 
+{.push raises: [Defect].}
+
 import
   # Standard library
   sets,
diff --git a/beacon_chain/spec/validator.nim b/beacon_chain/spec/validator.nim
index c786e11ef..dc9416198 100644
--- a/beacon_chain/spec/validator.nim
+++ b/beacon_chain/spec/validator.nim
@@ -6,6 +6,8 @@
 
 # Helpers and functions pertaining to managing the validator set
 
+{.push raises: [Defect].}
+
 import
   options, nimcrypto, sequtils, math, tables,
   ./datatypes, ./digest, ./helpers
@@ -91,25 +93,27 @@ func compute_committee(indices: seq[ValidatorIndex], seed: Eth2Digest,
     index: uint64, count: uint64, stateCache: var StateCache): seq[ValidatorIndex] =
   ## Return the committee corresponding to ``indices``, ``seed``, ``index``,
   ## and committee ``count``.
+  try:
+    let
+      start = (len(indices).uint64 * index) div count
+      endIdx = (len(indices).uint64 * (index + 1)) div count
+      key = (indices.len, seed)
 
-  let
-    start = (len(indices).uint64 * index) div count
-    endIdx = (len(indices).uint64 * (index + 1)) div count
-    key = (indices.len, seed)
+    if key notin stateCache.beacon_committee_cache:
+      stateCache.beacon_committee_cache[key] =
+        get_shuffled_seq(seed, len(indices).uint64)
 
-  if key notin stateCache.beacon_committee_cache:
-    stateCache.beacon_committee_cache[key] =
-      get_shuffled_seq(seed, len(indices).uint64)
+    # These assertions from compute_shuffled_index(...)
+    let index_count = indices.len().uint64
+    doAssert endIdx <= index_count
+    doAssert index_count <= 2'u64^40
 
-  # These assertions from compute_shuffled_index(...)
-  let index_count = indices.len().uint64
-  doAssert endIdx <= index_count
-  doAssert index_count <= 2'u64^40
-
-  # In spec, this calls get_shuffled_index() every time, but that's wasteful
-  mapIt(
-    start.int .. (endIdx.int-1),
-    indices[stateCache.beacon_committee_cache[key][it]])
+    # In spec, this calls get_shuffled_index() every time, but that's wasteful
+    mapIt(
+      start.int .. (endIdx.int-1),
+      indices[stateCache.beacon_committee_cache[key][it]])
+  except KeyError:
+    raiseAssert("Cached entries are added before use")
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.10.1/specs/phase0/beacon-chain.md#get_beacon_committee
 func get_beacon_committee*(
@@ -119,26 +123,29 @@ func get_beacon_committee*(
   let
     epoch = compute_epoch_at_slot(slot)
 
-  ## This is a somewhat more fragile, but high-ROI, caching setup --
-  ## get_active_validator_indices() is slow to run in a loop and only
-  ## changes once per epoch.
-  if epoch notin cache.active_validator_indices_cache:
-    cache.active_validator_indices_cache[epoch] =
-      get_active_validator_indices(state, epoch)
+  try:
+    ## This is a somewhat more fragile, but high-ROI, caching setup --
+    ## get_active_validator_indices() is slow to run in a loop and only
+    ## changes once per epoch.
+    if epoch notin cache.active_validator_indices_cache:
+      cache.active_validator_indices_cache[epoch] =
+        get_active_validator_indices(state, epoch)
 
-  # Constant throughout an epoch
-  if epoch notin cache.committee_count_cache:
-    cache.committee_count_cache[epoch] =
-      get_committee_count_at_slot(state, slot)
+    # Constant throughout an epoch
+    if epoch notin cache.committee_count_cache:
+      cache.committee_count_cache[epoch] =
+        get_committee_count_at_slot(state, slot)
 
-  compute_committee(
-    cache.active_validator_indices_cache[epoch],
-    get_seed(state, epoch, DOMAIN_BEACON_ATTESTER),
-    (slot mod SLOTS_PER_EPOCH) * cache.committee_count_cache[epoch] +
-      index.uint64,
-    cache.committee_count_cache[epoch] * SLOTS_PER_EPOCH,
-    cache
-  )
+    compute_committee(
+      cache.active_validator_indices_cache[epoch],
+      get_seed(state, epoch, DOMAIN_BEACON_ATTESTER),
+      (slot mod SLOTS_PER_EPOCH) * cache.committee_count_cache[epoch] +
+        index.uint64,
+      cache.committee_count_cache[epoch] * SLOTS_PER_EPOCH,
+      cache
+    )
+  except KeyError:
+    raiseAssert "values are added to cache before using them"
 
 # Not from spec
 func get_empty_per_epoch_cache*(): StateCache =
diff --git a/beacon_chain/ssz.nim b/beacon_chain/ssz.nim
index dd88f764e..800b24c89 100644
--- a/beacon_chain/ssz.nim
+++ b/beacon_chain/ssz.nim
@@ -8,6 +8,10 @@
 # SSZ Serialization (simple serialize)
 # See https://github.com/ethereum/eth2.0-specs/blob/master/specs/simple-serialize.md
 
+# TODO Cannot override push, even though the function is annotated
+# nim-beacon-chain/beacon_chain/ssz.nim(212, 18) Error: can raise an unlisted exception: IOError
+#{.push raises: [Defect].}
+
 import
   stew/shims/macros, options, algorithm, options,
   stew/[bitops2, bitseqs, endians2, objects, varints, ptrops, ranges/ptr_arith], stint,
@@ -72,15 +76,15 @@ template sizePrefixed*[TT](x: TT): untyped =
 
 proc init*(T: type SszReader,
            stream: InputStream,
-           maxObjectSize = defaultMaxObjectSize): T =
+           maxObjectSize = defaultMaxObjectSize): T {.raises: [Defect].} =
   T(stream: stream, maxObjectSize: maxObjectSize)
 
-proc mount*(F: type SSZ, stream: InputStream, T: type): T =
+proc mount*(F: type SSZ, stream: InputStream, T: type): T {.raises: [Defect].} =
   mixin readValue
   var reader = init(SszReader, stream)
   reader.readValue(T)
 
-method formatMsg*(err: ref SszSizeMismatchError, filename: string): string {.gcsafe.} =
+method formatMsg*(err: ref SszSizeMismatchError, filename: string): string {.gcsafe, raises: [Defect].} =
   # TODO: implement proper error string
   "Serialisation error while processing " & filename
 
@@ -111,7 +115,7 @@ template toSszType*(x: auto): auto =
   elif useListType and x is List: seq[x.T](x)
   else: x
 
-proc writeFixedSized(c: var WriteCursor, x: auto) =
+proc writeFixedSized(c: var WriteCursor, x: auto) {.raises: [Defect, IOError].} =
   mixin toSszType
 
   when x is byte:
@@ -146,7 +150,7 @@ template supports*(_: type SSZ, T: type): bool =
   mixin toSszType
   anonConst compiles(fixedPortionSize toSszType(default(T)))
 
-func init*(T: type SszWriter, stream: OutputStream): T =
+func init*(T: type SszWriter, stream: OutputStream): T {.raises: [Defect].} =
   result.stream = stream
 
 template enumerateSubFields(holder, fieldVar, body: untyped) =
@@ -157,7 +161,7 @@ template enumerateSubFields(holder, fieldVar, body: untyped) =
 
 proc writeVarSizeType(w: var SszWriter, value: auto) {.gcsafe.}
 
-proc beginRecord*(w: var SszWriter, TT: type): auto =
+proc beginRecord*(w: var SszWriter, TT: type): auto {.raises: [Defect].} =
   type T = TT
   when isFixedSize(T):
     FixedSizedWriterCtx()
@@ -193,7 +197,7 @@ template endRecord*(w: var SszWriter, ctx: var auto) =
   when ctx is VarSizedWriterCtx:
     finalize ctx.fixedParts
 
-proc writeVarSizeType(w: var SszWriter, value: auto) =
+proc writeVarSizeType(w: var SszWriter, value: auto) {.raises: [Defect, IOError].} =
   trs "STARTING VAR SIZE TYPE"
   mixin toSszType
   type T = type toSszType(value)
@@ -230,7 +234,7 @@ proc writeVarSizeType(w: var SszWriter, value: auto) =
       writeField w, ctx, astToStr(field), field
     endRecord w, ctx
 
-proc writeValue*(w: var SszWriter, x: auto) {.gcsafe.} =
+proc writeValue*(w: var SszWriter, x: auto) {.gcsafe, raises: [Defect, IOError].} =
   mixin toSszType
   type T = type toSszType(x)
 
@@ -241,7 +245,7 @@ proc writeValue*(w: var SszWriter, x: auto) {.gcsafe.} =
   else:
     unsupported type(x)
 
-proc writeValue*[T](w: var SszWriter, x: SizePrefixed[T]) =
+proc writeValue*[T](w: var SszWriter, x: SizePrefixed[T]) {.raises: [Defect, IOError].} =
   var cursor = w.stream.delayVarSizeWrite(10)
   let initPos = w.stream.pos
   w.writeValue T(x)
@@ -260,7 +264,7 @@ template fromSszBytes*[T; N](_: type TypeWithMaxLen[T, N],
   mixin fromSszBytes
   fromSszBytes(T, bytes)
 
-proc readValue*[T](r: var SszReader, val: var T) =
+proc readValue*[T](r: var SszReader, val: var T) {.raises: [Defect, MalformedSszError, SszSizeMismatchError].} =
   when isFixedSize(T):
     const minimalSize = fixedPortionSize(T)
     if r.stream.readable(minimalSize):
@@ -272,7 +276,7 @@ proc readValue*[T](r: var SszReader, val: var T) =
     # the dynamic portion to consume the right number of bytes.
     val = readSszValue(r.stream.read(r.stream.endPos), T)
 
-proc readValue*[T](r: var SszReader, val: var SizePrefixed[T]) =
+proc readValue*[T](r: var SszReader, val: var SizePrefixed[T]) {.raises: [Defect].} =
   let length = r.stream.readVarint(uint64)
   if length > r.maxObjectSize:
     raise newException(SszMaxSizeExceeded,
@@ -415,19 +419,23 @@ func mixInLength(root: Eth2Digest, length: int): Eth2Digest =
 
 func merkleizeSerializedChunks(merkleizer: SszChunksMerkleizer,
                                obj: auto): Eth2Digest =
-
-  var hashingStream = newSszHashingStream merkleizer
-  {.noSideEffect.}:
-    # We assume there are no side-effects here, because the
-    # SszHashingStream is keeping all of its output in memory.
-    hashingStream.writeFixedSized obj
-    hashingStream.flush
-  merkleizer.getFinalHash
+  try:
+    var hashingStream = newSszHashingStream merkleizer
+    {.noSideEffect.}:
+      # We assume there are no side-effects here, because the
+      # SszHashingStream is keeping all of its output in memory.
+      hashingStream.writeFixedSized obj
+      hashingStream.flush
+    merkleizer.getFinalHash
+  except IOError as e:
+    # Hashing shouldn't raise in theory but because of abstraction
+    # tax in the faststreams library, we have to do this at runtime
+    raiseAssert($e.msg)
 
 func merkleizeSerializedChunks(obj: auto): Eth2Digest =
   merkleizeSerializedChunks(SszChunksMerkleizer(), obj)
 
-func hash_tree_root*(x: auto): Eth2Digest {.gcsafe.}
+func hash_tree_root*(x: auto): Eth2Digest {.gcsafe, raises: [Defect].}
 
 template merkleizeFields(body: untyped): Eth2Digest {.dirty.} =
   var merkleizer {.inject.} = SszChunksMerkleizer()
@@ -546,7 +554,7 @@ func maxChunksCount(T: type, maxLen: static int64): int64 {.compileTime.} =
   else:
     unsupported T # This should never happen
 
-func hash_tree_root*(x: auto): Eth2Digest =
+func hash_tree_root*(x: auto): Eth2Digest {.raises: [Defect].} =
   trs "STARTING HASH TREE ROOT FOR TYPE ", name(type(x))
   mixin toSszType
   when x is SignedBeaconBlock:
diff --git a/beacon_chain/ssz/bytes_reader.nim b/beacon_chain/ssz/bytes_reader.nim
index bdef60519..fe93f4fba 100644
--- a/beacon_chain/ssz/bytes_reader.nim
+++ b/beacon_chain/ssz/bytes_reader.nim
@@ -1,3 +1,6 @@
+{.push raises: [Defect].}
+{.pragma: raisesssz, raises: [Defect, MalformedSszError, SszSizeMismatchError].}
+
 import
   typetraits, options,
   stew/[bitseqs, endians2, objects, bitseqs], serialization/testing/tracing,
@@ -10,19 +13,19 @@ template setOutputSize[R, T](a: var array[R, T], length: int) =
   if length != a.len:
     raise newException(MalformedSszError, "SSZ input of insufficient size")
 
-proc setOutputSize[T](s: var seq[T], length: int) {.inline.} =
+proc setOutputSize[T](s: var seq[T], length: int) {.inline, raisesssz.} =
   if sizeof(T) * length > maxListAllocation:
     raise newException(MalformedSszError, "SSZ list size is too large to fit in memory")
   s.setLen length
 
-proc setOutputSize(s: var string, length: int) {.inline.} =
+proc setOutputSize(s: var string, length: int) {.inline, raisesssz.} =
   if length > maxListAllocation:
     raise newException(MalformedSszError, "SSZ string is too large to fit in memory")
   s.setLen length
 
 # fromSszBytes copies the wire representation to a Nim variable,
 # assuming there's enough data in the buffer
-func fromSszBytes*(T: type SomeInteger, data: openarray[byte]): T =
+func fromSszBytes*(T: type SomeInteger, data: openarray[byte]): T {.raisesssz.} =
   ## Convert directly to bytes the size of the int. (e.g. ``uint16 = 2 bytes``)
   ## All integers are serialized as **little endian**.
   if data.len < sizeof(result):
@@ -30,14 +33,14 @@ func fromSszBytes*(T: type SomeInteger, data: openarray[byte]): T =
 
   T.fromBytesLE(data)
 
-func fromSszBytes*(T: type bool, data: openarray[byte]): T =
+func fromSszBytes*(T: type bool, data: openarray[byte]): T {.raisesssz.} =
   # TODO: spec doesn't say what to do if the value is >1 - we'll use the C
   #       definition for now, but maybe this should be a parse error instead?
   if data.len == 0 or data[0] > byte(1):
     raise newException(MalformedSszError, "invalid boolean value")
   data[0] == 1
 
-func fromSszBytes*(T: type Eth2Digest, data: openarray[byte]): T =
+func fromSszBytes*(T: type Eth2Digest, data: openarray[byte]): T {.raisesssz.} =
   if data.len < sizeof(result.data):
     raise newException(MalformedSszError, "SSZ input of insufficient size")
   copyMem(result.data.addr, unsafeAddr data[0], sizeof(result.data))
@@ -48,16 +51,16 @@ template fromSszBytes*(T: type Slot, bytes: openarray[byte]): Slot =
 template fromSszBytes*(T: type Epoch, bytes: openarray[byte]): Epoch =
   Epoch fromSszBytes(uint64, bytes)
 
-template fromSszBytes*(T: type enum, bytes: openarray[byte]): auto =
+template fromSszBytes*(T: type enum, bytes: openarray[byte]): auto  =
   T fromSszBytes(uint64, bytes)
 
 template fromSszBytes*(T: type BitSeq, bytes: openarray[byte]): auto =
   BitSeq @bytes
 
-func fromSszBytes*[N](T: type BitList[N], bytes: openarray[byte]): auto =
+func fromSszBytes*[N](T: type BitList[N], bytes: openarray[byte]): auto {.raisesssz.} =
   BitList[N] @bytes
 
-func fromSszBytes*[N](T: type BitArray[N], bytes: openarray[byte]): T =
+func fromSszBytes*[N](T: type BitArray[N], bytes: openarray[byte]): T {.raisesssz.} =
   # A bit vector doesn't have a marker bit, but we'll use the helper from
   # nim-stew to determine the position of the leading (marker) bit.
   # If it's outside the BitArray size, we have an overflow:
@@ -68,7 +71,7 @@ func fromSszBytes*[N](T: type BitArray[N], bytes: openarray[byte]): T =
 proc `[]`[T, U, V](s: openArray[T], x: HSlice[U, V]) {.error:
   "Please don't use openarray's [] as it allocates a result sequence".}
 
-func readSszValue*(input: openarray[byte], T: type): T =
+func readSszValue*(input: openarray[byte], T: type): T {.raisesssz.} =
   mixin fromSszBytes, toSszType
 
   type T {.used.} = type(result)
diff --git a/beacon_chain/ssz/dynamic_navigator.nim b/beacon_chain/ssz/dynamic_navigator.nim
index a336c9ea7..93a0624fc 100644
--- a/beacon_chain/ssz/dynamic_navigator.nim
+++ b/beacon_chain/ssz/dynamic_navigator.nim
@@ -1,3 +1,6 @@
+{.push raises: [Defect].}
+{.pragma: raisesssz, raises: [Defect, IOError, MalformedSszError, SszSizeMismatchError].}
+
 import
   strutils, parseutils,
   faststreams/output_stream, json_serialization/writer,
@@ -18,8 +21,7 @@ type
     fieldType: TypeInfo
     navigator: proc (m: MemRange): MemRange {. gcsafe
                                                noSideEffect
-                                               raises: [Defect,
-                                                        MalformedSszError] }
+                                               raisesssz }
   TypeInfo = ref object
     case kind: ObjKind
     of Record:
@@ -28,20 +30,19 @@ type
       elemType: TypeInfo
       navigator: proc (m: MemRange, idx: int): MemRange {. gcsafe
                                                            noSideEffect
-                                                           raises: [Defect,
-                                                                    MalformedSszError] }
+                                                           raisesssz }
     else:
       discard
 
     jsonPrinter: proc (m: MemRange,
                        outStream: OutputStream,
-                       pretty: bool) {.gcsafe.}
+                       pretty: bool) {.gcsafe, raisesssz.}
 
   DynamicSszNavigator* = object
     m: MemRange
     typ: TypeInfo
 
-proc jsonPrinterImpl[T](m: MemRange, outStream: OutputStream, pretty: bool) =
+proc jsonPrinterImpl[T](m: MemRange, outStream: OutputStream, pretty: bool) {.raisesssz.} =
   var typedNavigator = sszMount(m, T)
   var jsonWriter = init(JsonWriter, outStream, pretty)
   # TODO: it should be possible to serialize the navigator object
@@ -55,12 +56,12 @@ func findField(fields: seq[FieldInfo], name: string): FieldInfo =
     if field.name == name:
       return field
 
-func indexableNavigatorImpl[T](m: MemRange, idx: int): MemRange =
+func indexableNavigatorImpl[T](m: MemRange, idx: int): MemRange {.raisesssz.} =
   var typedNavigator = sszMount(m, T)
   getMemRange(typedNavigator[idx])
 
 func fieldNavigatorImpl[RecordType; FieldType;
-                        fieldName: static string](m: MemRange): MemRange {.raises: [MalformedSszError].} =
+                        fieldName: static string](m: MemRange): MemRange {.raisesssz.} =
   # TODO: Make sure this doesn't fail with a Defect when
   #       navigating to an inactive field in a case object.
   var typedNavigator = sszMount(m, RecordType)
@@ -97,12 +98,12 @@ func genTypeInfo(T: type): TypeInfo =
 
   result.jsonPrinter = jsonPrinterImpl[T]
 
-func `[]`*(n: DynamicSszNavigator, idx: int): DynamicSszNavigator =
+func `[]`*(n: DynamicSszNavigator, idx: int): DynamicSszNavigator {.raisesssz.} =
   doAssert n.typ.kind == Indexable
   DynamicSszNavigator(m: n.typ.navigator(n.m, idx), typ: n.typ.elemType)
 
 func navigate*(n: DynamicSszNavigator, path: string): DynamicSszNavigator {.
-               raises: [Defect, ValueError, MalformedSszError] .} =
+               raises: [Defect, KeyError, IOError, MalformedSszError, SszSizeMismatchError, ValueError] .} =
   case n.typ.kind
   of Record:
     let fieldInfo = n.typ.fields.findField(path)
@@ -129,11 +130,11 @@ template navigatePathImpl(nav, iterabalePathFragments: untyped) =
       return
 
 func navigatePath*(n: DynamicSszNavigator, path: string): DynamicSszNavigator {.
-                   raises: [Defect, ValueError, MalformedSszError] .} =
+                   raises: [Defect, IOError, ValueError, MalformedSszError, SszSizeMismatchError] .} =
   navigatePathImpl n, split(path, '/')
 
 func navigatePath*(n: DynamicSszNavigator, path: openarray[string]): DynamicSszNavigator {.
-                   raises: [Defect, ValueError, MalformedSszError] .} =
+                   raises: [Defect, IOError, ValueError, MalformedSszError, SszSizeMismatchError] .} =
   navigatePathImpl n, path
 
 func init*(T: type DynamicSszNavigator,
@@ -141,10 +142,10 @@ func init*(T: type DynamicSszNavigator,
   T(m: MemRange(startAddr: unsafeAddr bytes[0], length: bytes.len),
     typ: typeInfo(Navigated))
 
-proc writeJson*(n: DynamicSszNavigator, outStream: OutputStream, pretty = true) =
+proc writeJson*(n: DynamicSszNavigator, outStream: OutputStream, pretty = true) {.raisesssz.} =
   n.typ.jsonPrinter(n.m, outStream, pretty)
 
-func toJson*(n: DynamicSszNavigator, pretty = true): string =
+func toJson*(n: DynamicSszNavigator, pretty = true): string {.raisesssz.} =
   var outStream = memoryOutput()
   {.noSideEffect.}:
     # We are assuming that there are no side-effects here
@@ -154,4 +155,3 @@ func toJson*(n: DynamicSszNavigator, pretty = true): string =
     # from a file or a network device.
     writeJson(n, outStream, pretty)
   outStream.getOutput(string)
-
diff --git a/beacon_chain/ssz/navigator.nim b/beacon_chain/ssz/navigator.nim
index 6f8473e98..2c923e571 100644
--- a/beacon_chain/ssz/navigator.nim
+++ b/beacon_chain/ssz/navigator.nim
@@ -1,3 +1,6 @@
+{.push raises: [Defect].}
+{.pragma: raisesssz, raises: [Defect, MalformedSszError, SszSizeMismatchError].}
+
 import
   stew/[ptrops, objects], stew/ranges/ptr_arith,
   ./types, ./bytes_reader
@@ -35,7 +38,7 @@ template toOpenArray(m: MemRange): auto =
 
 func navigateToField*[T](n: SszNavigator[T],
                          fieldName: static string,
-                         FieldType: type): SszNavigator[FieldType] =
+                         FieldType: type): SszNavigator[FieldType] {.raisesssz.} =
   mixin toSszType
   type SszFieldType = type toSszType(default FieldType)
 
@@ -67,7 +70,7 @@ template `.`*[T](n: SszNavigator[T], field: untyped): auto =
   type FieldType = type(default(RecType).field)
   navigateToField(n, astToStr(field), FieldType)
 
-func indexVarSizeList(m: MemRange, idx: int): MemRange =
+func indexVarSizeList(m: MemRange, idx: int): MemRange {.raisesssz.} =
   template readOffset(pos): int =
     int fromSszBytes(uint32, makeOpenArray(offset(m.startAddr, pos), offsetSize))
 
@@ -114,7 +117,7 @@ template `[]`*[T](n: SszNavigator[seq[T]], idx: int): SszNavigator[T] =
 template `[]`*[R, T](n: SszNavigator[array[R, T]], idx: int): SszNavigator[T] =
   indexList(n, idx, T)
 
-func `[]`*[T](n: SszNavigator[T]): T =
+func `[]`*[T](n: SszNavigator[T]): T {.raisesssz.} =
   mixin toSszType, fromSszBytes
   type SszRepr = type(toSszType default(T))
   when type(SszRepr) is type(T):
@@ -122,6 +125,6 @@ func `[]`*[T](n: SszNavigator[T]): T =
   else:
     fromSszBytes(T, toOpenArray(n.m))
 
-converter derefNavigator*[T](n: SszNavigator[T]): T =
+converter derefNavigator*[T](n: SszNavigator[T]): T {.raisesssz.} =
   n[]
 
diff --git a/beacon_chain/ssz/types.nim b/beacon_chain/ssz/types.nim
index 474ad283a..5c9171006 100644
--- a/beacon_chain/ssz/types.nim
+++ b/beacon_chain/ssz/types.nim
@@ -1,3 +1,5 @@
+{.push raises: [Defect].}
+
 import
   tables, options,
   stew/shims/macros, stew/[objects, bitseqs],
@@ -185,9 +187,12 @@ proc fieldInfos*(RecordType: type): seq[tuple[name: string,
       fieldOffset = val[]
       val[] += fieldSize
     do:
-      let parentBranch = nestedUnder.getOrDefault(fieldCaseDiscriminator, "")
-      fieldOffset = offsetInBranch[parentBranch]
-      offsetInBranch[branchKey] = fieldOffset + fieldSize
+      try:
+        let parentBranch = nestedUnder.getOrDefault(fieldCaseDiscriminator, "")
+        fieldOffset = offsetInBranch[parentBranch]
+        offsetInBranch[branchKey] = fieldOffset + fieldSize
+      except KeyError as e:
+        raiseAssert e.msg
 
     result.add((fieldName, fieldOffset, fixedSize, branchKey))
 
diff --git a/beacon_chain/state_transition.nim b/beacon_chain/state_transition.nim
index 937441ecf..42687c41f 100644
--- a/beacon_chain/state_transition.nim
+++ b/beacon_chain/state_transition.nim
@@ -30,6 +30,8 @@
 # improvements to be made - other than that, keep things similar to spec for
 # now.
 
+{.push raises: [Defect].}
+
 import
   chronicles,
   ./extras, ./ssz, metrics,
@@ -95,11 +97,17 @@ proc process_slots*(state: var BeaconState, slot: Slot) {.nbench.}=
     let is_epoch_transition = (state.slot + 1) mod SLOTS_PER_EPOCH == 0
     if is_epoch_transition:
       # Note: Genesis epoch = 0, no need to test if before Genesis
-      beacon_previous_validators.set(get_epoch_validator_count(state))
+      try:
+        beacon_previous_validators.set(get_epoch_validator_count(state))
+      except Exception as e: # TODO https://github.com/status-im/nim-metrics/pull/22
+        trace "Couldn't update metrics", msg = e.msg
       process_epoch(state)
     state.slot += 1
     if is_epoch_transition:
-      beacon_current_validators.set(get_epoch_validator_count(state))
+      try:
+        beacon_current_validators.set(get_epoch_validator_count(state))
+      except Exception as e: # TODO https://github.com/status-im/nim-metrics/pull/22
+        trace "Couldn't update metrics", msg = e.msg
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/beacon-chain.md#verify_block_signature
 proc verify_block_signature*(
@@ -234,11 +242,17 @@ proc process_slots*(state: var HashedBeaconState, slot: Slot) =
     let is_epoch_transition = (state.data.slot + 1) mod SLOTS_PER_EPOCH == 0
     if is_epoch_transition:
       # Note: Genesis epoch = 0, no need to test if before Genesis
-      beacon_previous_validators.set(get_epoch_validator_count(state.data))
+      try:
+        beacon_previous_validators.set(get_epoch_validator_count(state.data))
+      except Exception as e: # TODO https://github.com/status-im/nim-metrics/pull/22
+        trace "Couldn't update metrics", msg = e.msg
       process_epoch(state.data)
     state.data.slot += 1
     if is_epoch_transition:
-      beacon_current_validators.set(get_epoch_validator_count(state.data))
+      try:
+        beacon_current_validators.set(get_epoch_validator_count(state.data))
+      except Exception as e: # TODO https://github.com/status-im/nim-metrics/pull/22
+        trace "Couldn't update metrics", msg = e.msg
     state.root = hash_tree_root(state.data)
 
 proc state_transition*(
diff --git a/beacon_chain/validator_keygen.nim b/beacon_chain/validator_keygen.nim
index 8ed302dc4..91ac14442 100644
--- a/beacon_chain/validator_keygen.nim
+++ b/beacon_chain/validator_keygen.nim
@@ -44,7 +44,7 @@ proc generateDeposits*(totalValidators: int,
     if randomKeys:
       (pubKey, privKey) = crypto.newKeyPair().tryGet()
     else:
-      privKey = makeInteropPrivKey(i)
+      privKey = makeInteropPrivKey(i).tryGet()
       pubKey = privKey.toPubKey()
 
     let dp = makeDeposit(pubKey, privKey)
diff --git a/beacon_chain/version.nim b/beacon_chain/version.nim
index c7159e8ee..0638a0c06 100644
--- a/beacon_chain/version.nim
+++ b/beacon_chain/version.nim
@@ -1,3 +1,5 @@
+{.push raises: [Defect].}
+
 when not defined(nimscript):
   import times
   let copyrights* = "Copyright (c) 2019-" & $(now().utc.year) & " Status Research & Development GmbH"
@@ -23,4 +25,3 @@ const
 
   fullVersionStr* =
     versionAsStr & " (" & gitRevision & ")"
-
diff --git a/tests/fork_choice/interpreter.nim b/tests/fork_choice/interpreter.nim
index 987ab36c9..f9406245d 100644
--- a/tests/fork_choice/interpreter.nim
+++ b/tests/fork_choice/interpreter.nim
@@ -9,12 +9,12 @@ import
   # Standard library
   std/strformat, std/tables, std/options,
   # Status libraries
-  stew/[result, endians2],
+  stew/[results, endians2],
   # Internals
   ../../beacon_chain/spec/[datatypes, digest],
   ../../beacon_chain/fork_choice/[fork_choice, fork_choice_types]
 
-export result, datatypes, digest, fork_choice, fork_choice_types, tables, options
+export results, datatypes, digest, fork_choice, fork_choice_types, tables, options
 
 func fakeHash*(index: SomeInteger): Eth2Digest =
   ## Create fake hashes
diff --git a/tests/test_interop.nim b/tests/test_interop.nim
index efa04ce24..3684870b7 100644
--- a/tests/test_interop.nim
+++ b/tests/test_interop.nim
@@ -119,7 +119,7 @@ suiteReport "Interop":
   timedTest "Mocked start private key":
     for i, k in privateKeys:
       let
-        key = makeInteropPrivKey(i)
+        key = makeInteropPrivKey(i)[]
         v = k.parse(UInt256, 16)
 
       check:
@@ -144,7 +144,7 @@ suiteReport "Interop":
 
     for i in 0..<64:
       let
-        privKey = makeInteropPrivKey(i)
+        privKey = makeInteropPrivKey(i)[]
       deposits.add(makeDeposit(privKey.toPubKey(), privKey))
 
     const genesis_time = 1570500000
diff --git a/tests/test_sync_manager.nim b/tests/test_sync_manager.nim
index bfc5d30d2..bf3c7fcba 100644
--- a/tests/test_sync_manager.nim
+++ b/tests/test_sync_manager.nim
@@ -1,3 +1,5 @@
+{.used.}
+
 import unittest
 import chronos
 import ../beacon_chain/sync_manager
diff --git a/vendor/nim-chronicles b/vendor/nim-chronicles
index 114cdccaa..3e7f422f1 160000
--- a/vendor/nim-chronicles
+++ b/vendor/nim-chronicles
@@ -1 +1 @@
-Subproject commit 114cdccaa087c54abcc4dad9ed3366af247de79e
+Subproject commit 3e7f422f11754732df673ed280389024e1ed3cb1