diff --git a/.gitmodules b/.gitmodules
index b04de0c9db..a343bb6c6e 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,4 +1,4 @@
 [submodule "priv/cabbage"]
 	path = priv/cabbage
 	url = git@github.com:omgnetwork/specs.git
-        branch = master
+        branch = master
\ No newline at end of file
diff --git a/apps/omg_watcher/lib/omg_watcher/block_validator.ex b/apps/omg_watcher/lib/omg_watcher/block_validator.ex
new file mode 100644
index 0000000000..8aae938ef1
--- /dev/null
+++ b/apps/omg_watcher/lib/omg_watcher/block_validator.ex
@@ -0,0 +1,67 @@
+# Copyright 2019-2020 OmiseGO Pte Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+defmodule OMG.Watcher.BlockValidator do
+  @moduledoc """
+  Operations related to block validation.
+  """
+
+  alias OMG.Block
+  alias OMG.Merkle
+  alias OMG.State.Transaction
+
+  @doc """
+  Executes stateless validation of a submitted block:
+  - Verifies that transactions are correctly formed.
+  - Verifies that given Merkle root matches reconstructed Merkle root.
+  """
+  @spec stateless_validate(Block.t()) :: {:ok, boolean()} | {:error, atom()}
+  def stateless_validate(submitted_block) do
+    with {:ok, recovered_transactions} <- verify_transactions(submitted_block.transactions),
+         {:ok, _block} <- verify_merkle_root(submitted_block, recovered_transactions) do
+      {:ok, true}
+    end
+  end
+
+  @spec verify_merkle_root(Block.t(), list(Transaction.Recovered.t())) ::
+          {:ok, Block.t()} | {:error, :mismatched_merkle_root}
+  defp verify_merkle_root(block, transactions) do
+    reconstructed_merkle_hash =
+      transactions
+      |> Enum.map(&Transaction.raw_txbytes/1)
+      |> Merkle.hash()
+
+    case block.hash do
+      ^reconstructed_merkle_hash -> {:ok, block}
+      _ -> {:error, :invalid_merkle_root}
+    end
+  end
+
+  @spec verify_transactions(transactions :: list(Transaction.Recovered.t())) ::
+          {:ok, list(Transaction.Recovered.t())}
+          | {:error, Transaction.Recovered.recover_tx_error()}
+  defp verify_transactions(transactions) do
+    transactions
+    |> Enum.reverse()
+    |> Enum.reduce_while({:ok, []}, fn tx, {:ok, already_recovered} ->
+      case Transaction.Recovered.recover_from(tx) do
+        {:ok, recovered} ->
+          {:cont, {:ok, [recovered | already_recovered]}}
+
+        error ->
+          {:halt, error}
+      end
+    end)
+  end
+end
diff --git a/apps/omg_watcher/test/omg_watcher/block_validator_test.exs b/apps/omg_watcher/test/omg_watcher/block_validator_test.exs
new file mode 100644
index 0000000000..baa367f656
--- /dev/null
+++ b/apps/omg_watcher/test/omg_watcher/block_validator_test.exs
@@ -0,0 +1,124 @@
+# Copyright 2019-2020 OmiseGO Pte Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+defmodule OMG.WatcherRPC.Web.Validator.BlockValidatorTest do
+  use ExUnit.Case, async: true
+  use OMG.WatcherRPC.Web, :controller
+
+  alias OMG.Merkle
+  alias OMG.State.Transaction
+  alias OMG.TestHelper
+  alias OMG.Watcher.BlockValidator
+
+  @alice TestHelper.generate_entity()
+  @bob TestHelper.generate_entity()
+  @eth OMG.Eth.zero_address()
+  @payment_tx_type OMG.WireFormatTypes.tx_type_for(:tx_payment_v1)
+
+  describe "stateless_validate/1" do
+    test "returns error if a transaction is not correctly formed (e.g. duplicate inputs)" do
+      input_1 = {1, 0, 0, @alice}
+      input_2 = {2, 0, 0, @alice}
+      input_3 = {3, 0, 0, @alice}
+
+      signed_valid_tx = TestHelper.create_signed([input_1, input_2], @eth, [{@bob, 10}])
+      signed_invalid_tx = TestHelper.create_signed([input_3, input_3], @eth, [{@bob, 10}])
+
+      %{sigs: sigs_valid} = signed_valid_tx
+      %{sigs: sigs_invalid} = signed_invalid_tx
+
+      txbytes_valid = Transaction.raw_txbytes(signed_valid_tx)
+      txbytes_invalid = Transaction.raw_txbytes(signed_invalid_tx)
+
+      [_, inputs_valid, outputs_valid, _, _] = ExRLP.decode(txbytes_valid)
+      [_, inputs_invalid, outputs_invalid, _, _] = ExRLP.decode(txbytes_invalid)
+
+      hash_valid = ExRLP.encode([sigs_valid, @payment_tx_type, inputs_valid, outputs_valid, 0, <<0::256>>])
+
+      hash_invalid =
+        ExRLP.encode([
+          sigs_invalid,
+          @payment_tx_type,
+          inputs_invalid,
+          outputs_invalid,
+          0,
+          <<0::256>>
+        ])
+
+      block = %{
+        hash: Merkle.hash([txbytes_valid, txbytes_invalid]),
+        number: 1000,
+        transactions: [hash_invalid, hash_valid]
+      }
+
+      assert {:error, :duplicate_inputs} == BlockValidator.stateless_validate(block)
+    end
+
+    test "accepts correctly formed transactions" do
+      recovered_tx_1 = TestHelper.create_recovered([{1, 0, 0, @alice}, {2, 0, 0, @alice}], @eth, [{@bob, 10}])
+      recovered_tx_2 = TestHelper.create_recovered([{3, 0, 0, @alice}, {4, 0, 0, @alice}], @eth, [{@bob, 10}])
+
+      signed_txbytes_1 = recovered_tx_1.signed_tx_bytes
+      signed_txbytes_2 = recovered_tx_2.signed_tx_bytes
+
+      merkle_root =
+        [recovered_tx_1, recovered_tx_2]
+        |> Enum.map(&Transaction.raw_txbytes/1)
+        |> Merkle.hash()
+
+      block = %{
+        hash: merkle_root,
+        number: 1000,
+        transactions: [signed_txbytes_1, signed_txbytes_2]
+      }
+
+      assert {:ok, true} == BlockValidator.stateless_validate(block)
+    end
+
+    test "returns error for non-matching Merkle root hash" do
+      recovered_tx_1 = TestHelper.create_recovered([{1, 0, 0, @alice}], @eth, [{@bob, 100}])
+      recovered_tx_2 = TestHelper.create_recovered([{2, 0, 0, @alice}], @eth, [{@bob, 100}])
+
+      signed_txbytes = Enum.map([recovered_tx_1, recovered_tx_2], fn tx -> tx.signed_tx_bytes end)
+
+      block = %{
+        hash: "0x0",
+        number: 1000,
+        transactions: signed_txbytes
+      }
+
+      assert {:error, :invalid_merkle_root} == BlockValidator.stateless_validate(block)
+    end
+
+    test "accepts matching Merkle root hash" do
+      recovered_tx_1 = TestHelper.create_recovered([{1, 0, 0, @alice}], @eth, [{@bob, 100}])
+      recovered_tx_2 = TestHelper.create_recovered([{2, 0, 0, @alice}], @eth, [{@bob, 100}])
+
+      signed_txbytes = Enum.map([recovered_tx_1, recovered_tx_2], fn tx -> tx.signed_tx_bytes end)
+
+      valid_merkle_root =
+        [recovered_tx_1, recovered_tx_2]
+        |> Enum.map(&Transaction.raw_txbytes/1)
+        |> Merkle.hash()
+
+      block = %{
+        hash: valid_merkle_root,
+        number: 1000,
+        transactions: signed_txbytes
+      }
+
+      assert {:ok, true} = BlockValidator.stateless_validate(block)
+    end
+  end
+end
diff --git a/apps/omg_watcher_rpc/lib/web/controllers/block.ex b/apps/omg_watcher_rpc/lib/web/controllers/block.ex
index 59b09f514c..2a860f3594 100644
--- a/apps/omg_watcher_rpc/lib/web/controllers/block.ex
+++ b/apps/omg_watcher_rpc/lib/web/controllers/block.ex
@@ -16,9 +16,11 @@ defmodule OMG.WatcherRPC.Web.Controller.Block do
   @moduledoc """
   Operations related to block.
   """
+  require Logger
 
   use OMG.WatcherRPC.Web, :controller
 
+  alias OMG.Watcher
   alias OMG.WatcherInfo.API.Block, as: InfoApiBlock
   alias OMG.WatcherRPC.Web.Validator
 
@@ -43,4 +45,20 @@ defmodule OMG.WatcherRPC.Web.Controller.Block do
       |> api_response(conn, :blocks)
     end
   end
+
+  @doc """
+  Executes stateful and stateless validation of a block.
+  """
+  def validate_block(conn, params) do
+    with {:ok, block} <- Validator.BlockConstraints.parse_to_validate(params) do
+      case Watcher.BlockValidator.stateless_validate(block) do
+        {:ok, true} ->
+          api_response(%{valid: true}, conn, :validate_block)
+
+        {:error, reason} ->
+          Logger.info("Block #{block.number} is invalid due to #{reason}")
+          api_response(%{valid: false}, conn, :validate_block)
+      end
+    end
+  end
 end
diff --git a/apps/omg_watcher_rpc/lib/web/controllers/fallback.ex b/apps/omg_watcher_rpc/lib/web/controllers/fallback.ex
index 74fb9c47b0..7d16750e1b 100644
--- a/apps/omg_watcher_rpc/lib/web/controllers/fallback.ex
+++ b/apps/omg_watcher_rpc/lib/web/controllers/fallback.ex
@@ -69,6 +69,10 @@ defmodule OMG.WatcherRPC.Web.Controller.Fallback do
       code: "transaction.create:self_transaction_not_supported",
       description: "This endpoint cannot be used to create merge or split transactions."
     },
+    invalid_merkle_root: %{
+      code: "block.validate:invalid_merkle_root",
+      description: "Block hash does not match reconstructed Merkle root."
+    },
     missing_signature: %{
       code: "submit_typed:missing_signature",
       description:
diff --git a/apps/omg_watcher_rpc/lib/web/router.ex b/apps/omg_watcher_rpc/lib/web/router.ex
index 7d25841775..6abf69557c 100644
--- a/apps/omg_watcher_rpc/lib/web/router.ex
+++ b/apps/omg_watcher_rpc/lib/web/router.ex
@@ -52,6 +52,8 @@ defmodule OMG.WatcherRPC.Web.Router do
 
     post("/account.get_exitable_utxos", Controller.Account, :get_exitable_utxos)
 
+    post("/block.validate", Controller.Block, :validate_block)
+
     post("/utxo.get_exit_data", Controller.Utxo, :get_utxo_exit)
     post("/utxo.get_challenge_data", Controller.Challenge, :get_utxo_challenge)
 
diff --git a/apps/omg_watcher_rpc/lib/web/validators/block_constraints.ex b/apps/omg_watcher_rpc/lib/web/validators/block_constraints.ex
index fd6a11460d..2943aae4d7 100644
--- a/apps/omg_watcher_rpc/lib/web/validators/block_constraints.ex
+++ b/apps/omg_watcher_rpc/lib/web/validators/block_constraints.ex
@@ -16,6 +16,10 @@ defmodule OMG.WatcherRPC.Web.Validator.BlockConstraints do
   @moduledoc """
   Validates `/block.all` query parameters
   """
+
+  use OMG.WatcherRPC.Web, :controller
+
+  alias OMG.Block
   alias OMG.WatcherRPC.Web.Validator.Helpers
 
   @doc """
@@ -30,4 +34,20 @@ defmodule OMG.WatcherRPC.Web.Validator.BlockConstraints do
 
     Helpers.validate_constraints(params, constraints)
   end
+
+  @doc """
+  Validates that a block submitted for validation is correctly formed.
+  """
+  @spec parse_to_validate(Block.t()) ::
+          {:error, {:validation_error, binary, any}} | {:ok, Block.t()}
+  def parse_to_validate(block) do
+    with {:ok, hash} <- expect(block, "hash", :hash),
+         {:ok, transactions} <- expect(block, "transactions", list: &is_hex/1),
+         {:ok, number} <- expect(block, "number", :pos_integer),
+         do: {:ok, %Block{hash: hash, transactions: transactions, number: number}}
+  end
+
+  defp is_hex(original) do
+    expect(%{"hash" => original}, "hash", :hex)
+  end
 end
diff --git a/apps/omg_watcher_rpc/lib/web/views/block.ex b/apps/omg_watcher_rpc/lib/web/views/block.ex
index cd27523abe..8bb88dcf83 100644
--- a/apps/omg_watcher_rpc/lib/web/views/block.ex
+++ b/apps/omg_watcher_rpc/lib/web/views/block.ex
@@ -34,4 +34,10 @@ defmodule OMG.WatcherRPC.Web.View.Block do
     |> Response.serialize_page(data_paging)
     |> WatcherRPCResponse.add_app_infos()
   end
+
+  def render("validate_block.json", %{response: block}) do
+    block
+    |> Response.serialize()
+    |> WatcherRPCResponse.add_app_infos()
+  end
 end
diff --git a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs.yaml b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs.yaml
index f10e7e17bc..2e6b50b966 100644
--- a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs.yaml
+++ b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs.yaml
@@ -22,6 +22,8 @@ tags:
       url: 'https://github.com/omisego/elixir-omg/blob/master/docs/api_specs/status_events_specs.md#byzantine-events'
   - name: Account
     description: Account related API.
+  - name: Block
+    description: Block-related API
   - name: UTXO
     description: UTXO related API.
   - name: Transaction
@@ -907,6 +909,136 @@ paths:
                         description: Something went wrong on the server
                         messages:
                           error_key: error_reason
+  /block.validate:
+    post:
+      tags:
+        - Block
+      summary: Verifies the stateless validity of a block.
+      description: |
+        Validates that the given transactions are correctly formed, and that the given hash corresponds to the reconstructed Merkle root hash.
+      operationId: validate
+      requestBody:
+        description: 'Block object with a hash, number and array of hexadecimal transaction bytes.'
+        required: true
+        content:
+          application/json:
+            schema:
+              title: BlockValidateBodySchema
+              type: object
+              properties:
+                hash:
+                  type: string
+                transactions:
+                  type: array
+                  items:
+                    type: string
+                number:
+                  type: integer
+              required:
+                - hash
+                - transactions
+                - number
+              example:
+                number: 1000
+                hash: 0xf8d083015ba98080808080940000...
+                transactions:
+                  - 0xf8c0f843b841fc6dbf49a4baa783ec576291f6083be5ea...
+                  - 0xf852c003eeed02eb94916f3753bd53e124d6d565ef1701...
+      responses:
+        '200':
+          description: Successful response to calling /block.validate
+          content:
+            application/json:
+              schema:
+                allOf:
+                  - description: The response schema for a successful operation
+                    type: object
+                    properties:
+                      version:
+                        type: string
+                      success:
+                        type: boolean
+                      data:
+                        type: object
+                      service_name:
+                        type: string
+                    required:
+                      - service_name
+                      - version
+                      - success
+                      - data
+                    example:
+                      service_name: watcher
+                      version: 1.0.0+abcdefa
+                      success: true
+                      data: {}
+                  - type: object
+                    properties:
+                      data:
+                        type: object
+                        properties:
+                          valid:
+                            type: boolean
+                    example:
+                      data:
+                        valid: false
+        '500':
+          description: Returns an internal server error
+          content:
+            application/json:
+              schema:
+                description: The response schema for an error
+                allOf:
+                  - description: The response schema for a successful operation
+                    type: object
+                    properties:
+                      version:
+                        type: string
+                      success:
+                        type: boolean
+                      data:
+                        type: object
+                      service_name:
+                        type: string
+                    required:
+                      - service_name
+                      - version
+                      - success
+                      - data
+                    example:
+                      service_name: watcher
+                      version: 1.0.0+abcdefa
+                      success: true
+                      data: {}
+                  - type: object
+                    properties:
+                      data:
+                        description: The object schema for an error
+                        type: object
+                        properties:
+                          object:
+                            type: string
+                          code:
+                            type: string
+                          description:
+                            type: string
+                          messages:
+                            type: object
+                        required:
+                          - object
+                          - code
+                          - description
+                          - messages
+                    required:
+                      - data
+                    example:
+                      success: false
+                      data:
+                        object: error
+                        code: 'server:internal_server_error'
+                        description: Something went wrong on the server
+                        messages:
+                          error_key: error_reason
   /utxo.get_challenge_data:
     post:
       tags:
diff --git a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/paths.yaml b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/paths.yaml
new file mode 100644
index 0000000000..25b25a76b9
--- /dev/null
+++ b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/paths.yaml
@@ -0,0 +1,15 @@
+block.validate:
+  post:
+    tags:
+      - Block
+    summary: Verifies the stateless validity of a block. 
+    description: > 
+      Validates that the given transactions are correctly formed, and that the given hash corresponds to the reconstructed Merkle root hash.
+    operationId: validate
+    requestBody:
+      $ref: 'request_bodies.yaml#/BlockValidateBodySchema'
+    responses:
+      200:
+        $ref: 'responses.yaml#/BlockValidateResponse'
+      500:
+        $ref: '../responses.yaml#/InternalServerError'
diff --git a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/request_bodies.yaml b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/request_bodies.yaml
new file mode 100644
index 0000000000..0854b928df
--- /dev/null
+++ b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/request_bodies.yaml
@@ -0,0 +1,25 @@
+BlockValidateBodySchema:
+  description: Block object with a hash, number and array of hexadecimal transaction bytes.
+  required: true
+  content:
+    application/json:
+      schema:
+        title: 'BlockValidateBodySchema'
+        type: object
+        properties:
+          hash:
+            type: string
+          transactions: 
+            type: array
+            items: 
+              type: string
+          number: 
+            type: integer
+        required:
+          - hash
+          - transactions
+          - number
+        example:
+          number: 1000
+          hash: '0xf8d083015ba98080808080940000...'
+          transactions: ["0xf8c0f843b841fc6dbf49a4baa783ec576291f6083be5ea...", "0xf852c003eeed02eb94916f3753bd53e124d6d565ef1701..." ]
diff --git a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/response_schemas.yaml b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/response_schemas.yaml
new file mode 100644
index 0000000000..b95fc00272
--- /dev/null
+++ b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/response_schemas.yaml
@@ -0,0 +1,11 @@
+BlockValidateResponseSchema:
+  allOf:
+  - $ref: '../response_schemas.yaml#/WatcherBaseResponseSchema'
+  - type: object
+    properties:
+      data:
+        type: object
+        $ref: 'schemas.yaml#/BlockValidateSchema'
+    example:
+      data:
+        valid: false
diff --git a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/responses.yaml b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/responses.yaml
new file mode 100644
index 0000000000..1a9a739797
--- /dev/null
+++ b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/responses.yaml
@@ -0,0 +1,6 @@
+BlockValidateResponse:
+  description: Successful response to calling /block.validate
+  content:
+    application/json:
+      schema:
+        $ref: 'response_schemas.yaml#/BlockValidateResponseSchema'
diff --git a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/schemas.yaml b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/schemas.yaml
new file mode 100644
index 0000000000..7cdca8787a
--- /dev/null
+++ b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/block/schemas.yaml
@@ -0,0 +1,5 @@
+BlockValidateSchema:
+  type: object
+  properties:
+    valid:
+      type: boolean
diff --git a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/swagger.yaml b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/swagger.yaml
index e5ca09fed7..d16507831a 100644
--- a/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/swagger.yaml
+++ b/apps/omg_watcher_rpc/priv/swagger/security_critical_api_specs/swagger.yaml
@@ -25,6 +25,8 @@ tags:
       url: "https://github.com/omisego/elixir-omg/blob/master/docs/api_specs/status_events_specs.md#byzantine-events"
   - name: Account
     description: Account related API.
+  - name: Block
+    description: Block-related API
   - name: UTXO
     description: UTXO related API.
   - name: Transaction
@@ -41,6 +43,8 @@ paths:
     $ref: 'status/paths.yaml#/status.get'
   /account.get_exitable_utxos:
     $ref: 'account/paths.yaml#/account.get_exitable_utxos'
+  /block.validate:
+    $ref: 'block/paths.yaml#/block.validate'
   /utxo.get_challenge_data:
     $ref: 'utxo/paths.yaml#/utxo.get_challenge_data'
   /utxo.get_exit_data:
diff --git a/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/controllers/block_test.exs b/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/controllers/block_test.exs
index 9291e7c57a..1a1099c335 100644
--- a/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/controllers/block_test.exs
+++ b/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/controllers/block_test.exs
@@ -16,11 +16,28 @@ defmodule OMG.WatcherRPC.Web.Controller.BlockTest do
   use ExUnitFixtures
   use ExUnit.Case, async: false
   use OMG.WatcherInfo.Fixtures
+  use OMG.WatcherRPC.Web, :controller
 
   import OMG.WatcherInfo.Factory
 
+  alias OMG.Eth.Encoding
+  alias OMG.Merkle
+  alias OMG.State.Transaction
+  alias OMG.TestHelper
+  alias OMG.WireFormatTypes
+
   alias Support.WatcherHelper
 
+  @valid_block %{
+    hash: "0x" <> String.duplicate("00", 32),
+    number: 1000,
+    transactions: ["0x00"]
+  }
+  @eth OMG.Eth.zero_address()
+  @alice OMG.TestHelper.generate_entity()
+  @bob OMG.TestHelper.generate_entity()
+  @payment_tx_type WireFormatTypes.tx_type_for(:tx_payment_v1)
+
   describe "get_block/2" do
     @tag fixtures: [:initial_blocks]
     test "/block.get returns correct block if existent" do
@@ -40,7 +57,9 @@ defmodule OMG.WatcherRPC.Web.Controller.BlockTest do
       expected = %{
         "code" => "operation:bad_request",
         "description" => "Parameters required by this operation are missing or incorrect.",
-        "messages" => %{"validation_error" => %{"parameter" => "blknum", "validator" => ":integer"}},
+        "messages" => %{
+          "validation_error" => %{"parameter" => "blknum", "validator" => ":integer"}
+        },
         "object" => "error"
       }
 
@@ -55,7 +74,9 @@ defmodule OMG.WatcherRPC.Web.Controller.BlockTest do
       expected = %{
         "code" => "operation:bad_request",
         "description" => "Parameters required by this operation are missing or incorrect.",
-        "messages" => %{"validation_error" => %{"parameter" => "blknum", "validator" => ":integer"}},
+        "messages" => %{
+          "validation_error" => %{"parameter" => "blknum", "validator" => ":integer"}
+        },
         "object" => "error"
       }
 
@@ -131,4 +152,125 @@ defmodule OMG.WatcherRPC.Web.Controller.BlockTest do
              } = response
     end
   end
+
+  describe "validate_block/2" do
+    @tag fixtures: [:phoenix_ecto_sandbox]
+    test "returns the error API response if a parameter is incorectly formed" do
+      invalid_hash = "0x1234"
+      invalid_params = Map.replace!(@valid_block, :hash, invalid_hash)
+
+      %{"data" => data} = WatcherHelper.rpc_call("block.validate", invalid_params, 200)
+
+      expected = %{
+        "code" => "operation:bad_request",
+        "description" => "Parameters required by this operation are missing or incorrect.",
+        "messages" => %{
+          "validation_error" => %{
+            "parameter" => "hash",
+            "validator" => "{:length, 32}"
+          }
+        },
+        "object" => "error"
+      }
+
+      assert expected == data
+    end
+
+    @tag fixtures: [:phoenix_ecto_sandbox]
+    test "returns the expected error if the block hash does not match the reconstructed Merkle root" do
+      recovered_tx_1 = TestHelper.create_recovered([{1, 0, 0, @alice}], @eth, [{@bob, 100}])
+      recovered_tx_2 = TestHelper.create_recovered([{2, 0, 0, @alice}], @eth, [{@bob, 100}])
+
+      signed_txbytes =
+        [recovered_tx_1, recovered_tx_2]
+        |> Enum.map(fn tx -> tx.signed_tx_bytes end)
+        |> Enum.map(&Encoding.to_hex/1)
+
+      invalid_merkle_root = "0x" <> String.duplicate("00", 32)
+
+      params = %{
+        hash: invalid_merkle_root,
+        number: 1000,
+        transactions: signed_txbytes
+      }
+
+      %{"data" => data} = WatcherHelper.rpc_call("block.validate", params, 200)
+
+      assert data == %{"valid" => false}
+    end
+
+    @tag fixtures: [:phoenix_ecto_sandbox]
+    test "returns the expected error if the transactions are incorrectly formed" do
+      input_1 = {1, 0, 0, @alice}
+      input_2 = {2, 0, 0, @alice}
+      input_3 = {3, 0, 0, @alice}
+
+      signed_valid_tx = TestHelper.create_signed([input_1, input_2], @eth, [{@bob, 10}])
+      signed_invalid_tx = TestHelper.create_signed([input_3, input_3], @eth, [{@bob, 10}])
+
+      %{sigs: sigs_valid} = signed_valid_tx
+      %{sigs: sigs_invalid} = signed_invalid_tx
+
+      txbytes_valid = Transaction.raw_txbytes(signed_valid_tx)
+      txbytes_invalid = Transaction.raw_txbytes(signed_invalid_tx)
+
+      [_, inputs_valid, outputs_valid, _, _] = ExRLP.decode(txbytes_valid)
+      [_, inputs_invalid, outputs_invalid, _, _] = ExRLP.decode(txbytes_invalid)
+
+      hash_valid =
+        [sigs_valid, @payment_tx_type, inputs_valid, outputs_valid, 0, <<0::256>>]
+        |> ExRLP.encode()
+        |> Encoding.to_hex()
+
+      hash_invalid =
+        [sigs_invalid, @payment_tx_type, inputs_invalid, outputs_invalid, 0, <<0::256>>]
+        |> ExRLP.encode()
+        |> Encoding.to_hex()
+
+      merkle_root = [txbytes_invalid, txbytes_valid] |> Merkle.hash() |> Encoding.to_hex()
+
+      params = %{
+        hash: merkle_root,
+        transactions: [hash_invalid, hash_valid],
+        number: 1000
+      }
+
+      # Sanity check
+      assert {:ok, Encoding.from_hex(merkle_root)} == expect(%{hash: merkle_root}, :hash, :hash)
+
+      %{"data" => data} = WatcherHelper.rpc_call("block.validate", params, 200)
+
+      assert data == %{"valid" => false}
+    end
+
+    @tag fixtures: [:phoenix_ecto_sandbox]
+    test "returns the block if it is valid" do
+      recovered_tx_1 = TestHelper.create_recovered([{1, 0, 0, @alice}], @eth, [{@bob, 100}])
+      recovered_tx_2 = TestHelper.create_recovered([{2, 0, 0, @alice}], @eth, [{@bob, 100}])
+
+      signed_txbytes =
+        [recovered_tx_1, recovered_tx_2]
+        |> Enum.map(fn tx -> tx.signed_tx_bytes end)
+        |> Enum.map(&Encoding.to_hex/1)
+
+      valid_merkle_root =
+        [recovered_tx_1, recovered_tx_2]
+        |> Enum.map(&Transaction.raw_txbytes/1)
+        |> Merkle.hash()
+        |> Encoding.to_hex()
+
+      # Sanity check
+      assert {:ok, Encoding.from_hex(valid_merkle_root)} == expect(%{hash: valid_merkle_root}, :hash, :hash)
+
+      params = %{
+        hash: valid_merkle_root,
+        number: 1000,
+        transactions: signed_txbytes
+      }
+
+      %{"data" => data} = WatcherHelper.rpc_call("block.validate", params, 200)
+
+      assert data == %{"valid" => true}
+    end
+  end
 end
diff --git a/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/validators/block_constraints_test.exs b/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/validators/block_constraints_test.exs
index c694936743..c82158ff2e 100644
--- a/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/validators/block_constraints_test.exs
+++ b/apps/omg_watcher_rpc/test/omg_watcher_rpc/web/validators/block_constraints_test.exs
@@ -17,6 +17,12 @@ defmodule OMG.WatcherRPC.Web.Validator.BlockConstraintsTest do
 
   alias OMG.WatcherRPC.Web.Validator.BlockConstraints
 
+  @valid_block %{
+    "hash" => "0x" <> String.duplicate("00", 32),
+    "number" => 1000,
+    "transactions" => ["0x00"]
+  }
+
   describe "parse/1" do
     test "returns page and limit constraints when given page and limit params" do
       request_data = %{"page" => 1, "limit" => 100}
@@ -58,4 +64,38 @@ defmodule OMG.WatcherRPC.Web.Validator.BlockConstraintsTest do
       assert BlockConstraints.parse(%{"page" => "abcd"}) == {:error, {:validation_error, "page", :integer}}
     end
   end
+
+  describe "parse_to_validate/1" do
+    test "rejects invalid Merkle root hash" do
+      invalid_hash = "0x1234"
+      invalid_block = Map.replace!(@valid_block, "hash", invalid_hash)
+
+      assert {:error, {:validation_error, "hash", {:length, 32}}} ==
+               BlockConstraints.parse_to_validate(invalid_block)
+    end
+
+    test "rejects non-list transactions parameter" do
+      invalid_transactions_param = "0x1234"
+      invalid_block = Map.replace!(@valid_block, "transactions", invalid_transactions_param)
+
+      assert {:error, {:validation_error, "transactions", :list}} ==
+               BlockConstraints.parse_to_validate(invalid_block)
+    end
+
+    test "rejects non-hex elements in transactions list" do
+      invalid_tx_rlp = "0xZ"
+      invalid_block = Map.replace!(@valid_block, "transactions", [invalid_tx_rlp])
+
+      assert {:error, {:validation_error, "transactions.hash", :hex}} ==
+               BlockConstraints.parse_to_validate(invalid_block)
+    end
+
+    test "rejects invalid block number parameter" do
+      invalid_blknum = "ONE THOUSAND"
+      invalid_block = Map.replace!(@valid_block, "number", invalid_blknum)
+
+      assert {:error, {:validation_error, "number", :integer}} ==
+               BlockConstraints.parse_to_validate(invalid_block)
+    end
+  end
 end
diff --git a/priv/cabbage b/priv/cabbage
index cd262a3b62..96d67f4e06 160000
--- a/priv/cabbage
+++ b/priv/cabbage
@@ -1 +1 @@
-Subproject commit cd262a3b624a347b05208b154e0c2d7f85dd92a9
+Subproject commit 96d67f4e065aad020dfde111419e95e397f443e8