diff --git a/poseidon2/io.nim b/poseidon2/io.nim
index 06827d1..33b822f 100644
--- a/poseidon2/io.nim
+++ b/poseidon2/io.nim
@@ -3,6 +3,10 @@ import constantine/math/arithmetic
 import constantine/math/io/io_bigints
 
 func unmarshal*(_: type F, bytes: openArray[byte]): F =
+  ## Converts bytes into a field element. The byte array is interpreted as a
+  ## canonical little-endian big integer. The array should be of length 31 bytes
+  ## or less to ensure that it fits in a field of 254 bits. The remaining
+  ## 6 most-significant bits are set to 0.
   assert bytes.len <= 31
   var padded: array[32, byte]
   copyMem(addr padded[0], unsafeAddr bytes[0], bytes.len)
@@ -10,6 +14,8 @@ func unmarshal*(_: type F, bytes: openArray[byte]): F =
   return F.fromBig(bigint)
 
 func unmarshal*(_: type seq[F], bytes: openArray[byte]): seq[F] =
+  ## Converts bytes into field elements. The byte array is converted 31 bytes at
+  ## a time with the `F.unmarshal()` function.
   const chunkLen = 31
   var elements: seq[F]
   var chunkStart = 0