diff --git a/unison-share-api/package.yaml b/unison-share-api/package.yaml
index 77bf436d8a..954e80f9ce 100644
--- a/unison-share-api/package.yaml
+++ b/unison-share-api/package.yaml
@@ -14,6 +14,7 @@ dependencies:
   - async
   - base
   - binary
+  - bytes
   - bytestring
   - containers
   - directory
@@ -42,6 +43,7 @@ dependencies:
   - transformers
   - unison-codebase
   - unison-codebase-sqlite
+  - unison-codebase-sqlite-hashing-v2
   - unison-core
   - unison-core1
   - unison-hash
diff --git a/unison-share-api/src/Unison/Sync/HashValidation.hs b/unison-share-api/src/Unison/Sync/HashValidation.hs
new file mode 100644
index 0000000000..607213767c
--- /dev/null
+++ b/unison-share-api/src/Unison/Sync/HashValidation.hs
@@ -0,0 +1,90 @@
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DuplicateRecordFields #-}
+
+-- | Module for validating hashes of entities received/sent via sync.
+module Unison.Sync.HashValidation
+  ( HashValidationError (..),
+    validateEntityHash,
+  )
+where
+
+import Control.Exception
+import Data.ByteString qualified as BS
+import Data.Bytes.Get (runGetS)
+import U.Codebase.HashTags
+import U.Codebase.Sqlite.Branch.Format qualified as BranchFormat
+import U.Codebase.Sqlite.Decode qualified as Decode
+import U.Codebase.Sqlite.Entity qualified as Entity
+import U.Codebase.Sqlite.HashHandle qualified as HH
+import U.Codebase.Sqlite.Orphans ()
+import U.Codebase.Sqlite.Serialization qualified as Serialization
+import U.Codebase.Sqlite.Term.Format qualified as TermFormat
+import U.Codebase.Sqlite.V2.HashHandle (v2HashHandle)
+import Unison.Hash (Hash)
+import Unison.Hash32 (Hash32)
+import Unison.Hash32 qualified as Hash32
+import Unison.Prelude
+import Unison.Sync.Common qualified as Share
+import Unison.Sync.Types qualified as Share
+
+data HashValidationError
+  = MismatchedNamespaceHash (Hash {- expected hash -}) (Hash {- actual hash -})
+  | MismatchedTermHash (Hash {- expected hash -}) (Hash {- actual hash -})
+  | NamespaceDiffsAreUnsupported
+  | InvalidByteEncoding Text
+  deriving stock (Show, Eq, Ord)
+  deriving anyclass (Exception)
+
+data UnexpectedHashMismatch = UnexpectedHashMismatch
+  { providedHash :: ComponentHash,
+    actualHash :: ComponentHash
+  }
+  deriving stock (Show)
+
+-- | Note: We currently only validate Namespace hashes.
+-- We should add more validation as more entities are shared.
+validateEntityHash :: Hash32 -> Share.Entity Text Hash32 Hash32 -> Maybe HashValidationError
+validateEntityHash expectedHash32 entity = do
+  case Share.entityToTempEntity id entity of
+    Entity.TC (TermFormat.SyncTerm localComp) -> do
+      validateTerm expectedHash localComp
+    Entity.N (BranchFormat.SyncDiff {}) -> do
+      (Just NamespaceDiffsAreUnsupported)
+    Entity.N (BranchFormat.SyncFull localIds (BranchFormat.LocalBranchBytes bytes)) -> do
+      validateBranchFull expectedHash localIds bytes
+    _ -> Nothing
+  where
+    expectedHash :: Hash
+    expectedHash = Hash32.toHash expectedHash32
+
+validateBranchFull ::
+  Hash ->
+  BranchFormat.BranchLocalIds' Text Hash32 Hash32 (Hash32, Hash32) ->
+  BS.ByteString ->
+  (Maybe HashValidationError)
+validateBranchFull expectedHash localIds bytes = do
+  case runGetS Serialization.getLocalBranch bytes of
+    Left e -> Just $ InvalidByteEncoding ("Failed to decode local branch bytes: " <> tShow e)
+    Right localBranch -> do
+      let localIds' =
+            localIds
+              { BranchFormat.branchDefnLookup = ComponentHash . Hash32.toHash <$> BranchFormat.branchDefnLookup localIds,
+                BranchFormat.branchPatchLookup = PatchHash . Hash32.toHash <$> BranchFormat.branchPatchLookup localIds,
+                BranchFormat.branchChildLookup =
+                  BranchFormat.branchChildLookup localIds
+                    <&> bimap (BranchHash . Hash32.toHash) (CausalHash . Hash32.toHash)
+              }
+      let actualHash =
+            HH.hashBranchFormatFull v2HashHandle localIds' localBranch
+      if actualHash == BranchHash expectedHash
+        then Nothing
+        else Just $ MismatchedNamespaceHash expectedHash (unBranchHash actualHash)
+
+validateTerm :: Hash -> (TermFormat.SyncLocallyIndexedComponent' Text Hash32) -> (Maybe HashValidationError)
+validateTerm expectedHash syncLocalComp@(TermFormat.SyncLocallyIndexedComponent comps) = do
+  case Decode.unsyncTermComponent syncLocalComp of
+    Left _ -> Just (InvalidByteEncoding $ "Failed to decode term component bytes" <> tShow comps)
+    Right localComp -> do
+      case HH.verifyTermFormatHash v2HashHandle (ComponentHash expectedHash) (TermFormat.Term localComp) of
+        Nothing -> Nothing
+        Just (HH.HashMismatch {expectedHash, actualHash}) -> Just $ MismatchedTermHash expectedHash actualHash
diff --git a/unison-share-api/unison-share-api.cabal b/unison-share-api/unison-share-api.cabal
index 19a0827673..ee5ed900d9 100644
--- a/unison-share-api/unison-share-api.cabal
+++ b/unison-share-api/unison-share-api.cabal
@@ -45,6 +45,7 @@ library
       Unison.Server.Types
       Unison.Sync.API
       Unison.Sync.Common
+      Unison.Sync.HashValidation
       Unison.Sync.Types
       Unison.Util.Find
   hs-source-dirs:
@@ -86,6 +87,7 @@ library
     , async
     , base
     , binary
+    , bytes
     , bytestring
     , containers
     , directory
@@ -114,6 +116,7 @@ library
     , transformers
     , unison-codebase
     , unison-codebase-sqlite
+    , unison-codebase-sqlite-hashing-v2
     , unison-core
     , unison-core1
     , unison-hash