diff --git a/web3/builder_api.nim b/web3/builder_api.nim
new file mode 100644
index 0000000..91b563a
--- /dev/null
+++ b/web3/builder_api.nim
@@ -0,0 +1,14 @@
+import
+  strutils,
+  json_serialization/std/[sets, net], serialization/errors,
+  json_rpc/[client, jsonmarshal],
+  conversions, builder_api_types, engine_api_types
+
+export
+  builder_api_types, conversions
+
+from os import DirSep, AltSep
+template sourceDir: string = currentSourcePath.rsplit({DirSep, AltSep}, 1)[0]
+
+createRpcSigs(RpcClient, sourceDir & "/builder_api_callsigs.nim")
+
diff --git a/web3/builder_api_callsigs.nim b/web3/builder_api_callsigs.nim
new file mode 100644
index 0000000..c05167f
--- /dev/null
+++ b/web3/builder_api_callsigs.nim
@@ -0,0 +1,6 @@
+# https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#api-docs
+
+import ethtypes, builder_api_types, engine_api_types
+
+proc builder_getPayloadHeaderV1(payloadId: PayloadID): ExecutionPayloadHeaderV1
+proc builder_proposeBlindedBlockV1(blck: SignedBlindedBeaconBlock): ExecutionPayloadV1
diff --git a/web3/builder_api_types.nim b/web3/builder_api_types.nim
new file mode 100644
index 0000000..1be133f
--- /dev/null
+++ b/web3/builder_api_types.nim
@@ -0,0 +1,47 @@
+import
+  ethtypes
+
+export
+  ethtypes
+
+type
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/bellatrix/beacon-chain.md#executionpayloadheader
+  ExecutionPayloadHeaderV1* = object
+    parent_hash*: FixedBytes[32]
+    fee_recipient*: Address
+    state_root*: FixedBytes[32]
+    receipts_root*: FixedBytes[32]
+    logs_bloom*: FixedBytes[256]
+    random*: FixedBytes[32]
+    block_number*: Quantity
+    gas_limit*: Quantity
+    gas_used*: Quantity
+    timestamp*: Quantity
+    extra_data*: string    # List[byte, MAX_EXTRA_DATA_BYTES]
+    base_fee_per_gas*: FixedBytes[32]  # base fee introduced in EIP-1559, little-endian serialized
+
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#blindedbeaconblockbody
+  BlindedBeaconBlockBody* = object
+    randao_reveal*: FixedBytes[96]
+    eth1_data*: string # Eth1Data
+    graffiti*: FixedBytes[32]
+    proposer_slashings*: string # List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
+    attester_slashings*: string # List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
+    attestations*: string # List[Attestation, MAX_ATTESTATIONS]
+    voluntary_exits*: string # List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
+    sync_aggregate*: string # SyncAggregate
+    execution_payload_header*: ExecutionPayloadHeaderV1
+
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#blindedbeaconblock
+  BlindedBeaconBlock* = object
+    slot*: Quantity
+    proposer_index*: Quantity
+    parent_root*: FixedBytes[32]
+    state_root*: FixedBytes[32]
+    body*: BlindedBeaconBlockBody
+
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#signedblindedbeaconblock
+  SignedBlindedBeaconBlock* = object
+    message*: BlindedBeaconBlock
+    signature*: FixedBytes[96]
+