Blockscout Smart Contract Verification API

Contract verification is available through the PRO API’s Etherscan-compatible RPC route — module=contract. One key works across every Blockscout-supported chain: swap chain_id to move between them. Get a free key at dev.blockscout.com.

All calls in this guide share the same base pattern:

https://api.blockscout.com/v2/api?chain_id=<chain_id>&module=contract&action=<action>&apikey=<your_pro_api_key>

Swap <chain_id> for the target chain (1 for Ethereum, 8453 for Base, 11155111 for Sepolia, and so on — full list at dev.blockscout.com).

Contract addresses, source code, and other variables in the examples below are illustrative. Replace them with your own contract’s details.

If you’re running a self-hosted Blockscout instance, or verifying on a chain the PRO API doesn’t cover yet, the same actions work against that instance’s own API directly — see the Contract module RPC reference for the per-instance version of these calls.

License type

You can specify the license type of the smart contract as string or number. For example, for GNU General Public License v2.0 (GNU GPLv2) you could pass either 4 or "gnu_gpl_v2". We are supporting such types of license as:

No License (None)
The Unlicense (Unlicense)
MIT License (MIT)
GNU General Public License v2.0 (GNU GPLv2)
GNU General Public License v3.0 (GNU GPLv3)
GNU Lesser General Public License v2.1 (GNU LGPLv2.1)
GNU Lesser General Public License v3.0 (GNU LGPLv3)
BSD 2-clause "Simplified" license (BSD-2-Clause)
BSD 3-clause "New" Or "Revised" license* (BSD-3-Clause)
Mozilla Public License 2.0 (MPL-2.0)
Open Software License 3.0 (OSL-3.0)
Apache 2.0 (Apache-2.0)
GNU Affero General Public License (GNU AGPLv3)
Business Source License (BSL 1.1)

API license types:

none
unlicense
mit
gnu_gpl_v2
gnu_gpl_v3
gnu_lgpl_v2_1
gnu_lgpl_v3
bsd_2_clause
bsd_3_clause
mpl_2_0
osl_3_0
apache_2_0
gnu_agpl_v3
bsl_1_1

Via flattened source code or standard JSON input

action=verifysourcecode The same action handles both cases — set codeformat to solidity-single-file for a flattened contract, or solidity-standard-json-input for a standard JSON input file (the format most build tools, like Hardhat and Foundry, generate automatically).

Params
Example Result

Parameter	Description
codeformat	`solidity-single-file` or `solidity-standard-json-input`
contractaddress	`string` containing the address hash of the contract
contractname	`string` name of the contract. Can be empty (`""`), just the name (`"ContractName"`), or path and name (`"contracts/contract_1.sol:ContractName"`)
compilerversion	`string` containing the compiler version for the contract
sourceCode	`string` standard input JSON or flattened Solidity code
optimizationUsed	`0`, `false`, `1`, or `true`. Set when `codeformat=solidity-single-file`
runs	`integer` optimization runs used during compilation. Set when `optimizationUsed` is `1` or `true`
evmversion	`string` EVM version. Set when `codeformat=solidity-single-file`
constructorArguments	optional `string` constructor argument data
autodetectConstructorArguments	optional `boolean` whether to auto-detect constructor arguments
licenseType	`string` or `number` license type — see License type above
libraryname1 / libraryaddress1	optional name and address of a linked library

{
  "message": "OK",
  "result": "b080b96bd06ad1c9341c2afb7e3730311388544961acde94",
  "status": "1"
}

The result is a guid — use it with checkverifystatus to poll for the outcome.

curl "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=verifysourcecode&apikey=<your_pro_api_key>" \
  --form 'contractaddress="0xYourContractAddress"' \
  --form 'sourceCode="// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.8.2 <0.9.0;

contract Storage {
    uint256 number;

    function store(uint256 num) public {
        number = num;
    }

    function retrieve() public view returns (uint256){
        return number;
    }
}"' \
  --form 'contractname="Storage"' \
  --form 'codeformat="solidity-single-file"' \
  --form 'compilerversion="v0.8.34+commit.80d5c536"' \
  --form 'optimizationUsed="0"' \
  --form 'evmversion="default"' \
  --form 'licenseType="3"'

const formData = new FormData();

formData.append("contractaddress", "0xYourContractAddress");
formData.append("sourceCode", sourceCode); // flattened Solidity or standard-json-input string
formData.append("contractname", "Storage");
formData.append("codeformat", "solidity-single-file"); // or "solidity-standard-json-input"
formData.append("compilerversion", "v0.8.34+commit.80d5c536");
formData.append("optimizationUsed", "0");
formData.append("evmversion", "default");
formData.append("licenseType", "3");

const response = await fetch(
  "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=verifysourcecode&apikey=<your_pro_api_key>",
  { method: "POST", body: formData }
);

const data = await response.json();

import requests

files = {
    "contractaddress": (None, "0xYourContractAddress"),
    "sourceCode": (None, source_code),  # flattened Solidity or standard-json-input string
    "contractname": (None, "Storage"),
    "codeformat": (None, "solidity-single-file"),  # or "solidity-standard-json-input"
    "compilerversion": (None, "v0.8.34+commit.80d5c536"),
    "optimizationUsed": (None, "0"),
    "evmversion": (None, "default"),
    "licenseType": (None, "3"),
}

response = requests.post(
    "https://api.blockscout.com/v2/api",
    params={"chain_id": "11155111", "module": "contract", "action": "verifysourcecode", "apikey": "<your_pro_api_key>"},
    files=files,
)

data = response.json()

Via Sourcify

action=verify_via_sourcify If the contract is already verified on Sourcify, Blockscout fetches the match from the repo automatically. Otherwise, upload the source files and JSON metadata file(s).

Params
Example Result

Parameter	Description
addressHash	`string` containing the address hash
files	`array` with source and metadata files

{
  "message": "OK",
  "result": {
    "ABI": "[...]",
    "CompilerVersion": "v0.8.34+commit.80d5c536",
    "ContractName": "Storage",
    "SourceCode": "// SPDX-License-Identifier: GPL-3.0..."
  },
  "status": "1"
}

curl "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=verify_via_sourcify&apikey=<your_pro_api_key>" \
  --form 'addressHash="0xYourContractAddress"' \
  --form 'files[0]=@./Storage.sol' \
  --form 'files[1]=@./metadata.json'

const formData = new FormData();

formData.append("addressHash", "0xYourContractAddress");
formData.append("files[0]", solFile);       // File or Blob for the .sol source
formData.append("files[1]", metadataFile);  // File or Blob for metadata.json

const response = await fetch(
  "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=verify_via_sourcify&apikey=<your_pro_api_key>",
  { method: "POST", body: formData }
);

const data = await response.json();

import requests

files = {
    "addressHash": (None, "0xYourContractAddress"),
    "files[0]": ("Storage.sol", open("Storage.sol", "rb")),
    "files[1]": ("metadata.json", open("metadata.json", "rb")),
}

response = requests.post(
    "https://api.blockscout.com/v2/api",
    params={"chain_id": "11155111", "module": "contract", "action": "verify_via_sourcify", "apikey": "<your_pro_api_key>"},
    files=files,
)

data = response.json()

Vyper contracts

action=verify_vyper_contract

Params
Example Result

Parameter	Description
addressHash	`string` containing the address hash of the contract
name	`string` containing the name of the contract
compilerVersion	`string` containing the compiler version for the contract
contractSourceCode	`string` containing the source code of the contract
constructorArguments	optional `string` constructor argument data

{
  "message": "OK",
  "result": {
    "ABI": "[...]",
    "CompilerVersion": "v0.3.7+commit.6020b8bb",
    "ContractName": "VyperStorage",
    "SourceCode": "# @version 0.3.7..."
  },
  "status": "1"
}

curl "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=verify_vyper_contract&apikey=<your_pro_api_key>" \
  --form 'addressHash="0xYourContractAddress"' \
  --form 'name="VyperStorage"' \
  --form 'compilerVersion="v0.3.7+commit.6020b8bb"' \
  --form 'contractSourceCode="<your Vyper source code>"'

const formData = new FormData();

formData.append("addressHash", "0xYourContractAddress");
formData.append("name", "VyperStorage");
formData.append("compilerVersion", "v0.3.7+commit.6020b8bb");
formData.append("contractSourceCode", vyperSourceCode);

const response = await fetch(
  "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=verify_vyper_contract&apikey=<your_pro_api_key>",
  { method: "POST", body: formData }
);

const data = await response.json();

import requests

files = {
    "addressHash": (None, "0xYourContractAddress"),
    "name": (None, "VyperStorage"),
    "compilerVersion": (None, "v0.3.7+commit.6020b8bb"),
    "contractSourceCode": (None, vyper_source_code),
}

response = requests.post(
    "https://api.blockscout.com/v2/api",
    params={"chain_id": "11155111", "module": "contract", "action": "verify_vyper_contract", "apikey": "<your_pro_api_key>"},
    files=files,
)

data = response.json()

Only single-file Vyper verification is confirmed on this route. If you need Vyper multi-part or Vyper standard-JSON-input verification specifically, those aren’t confirmed to have a PRO API equivalent yet — use the per-instance route for those cases in the meantime.

Multiple raw source files

Blockscout’s REST API has a dedicated “multi-part” mode for submitting several unflattened .sol files at once. The PRO API’s verifysourcecode action doesn’t have a direct equivalent for that — instead, build a standard JSON input file (most toolchains generate one automatically, e.g. under artifacts/build-info/ in Hardhat) and submit it with codeformat=solidity-standard-json-input in the flattened / standard JSON section above. That covers the same multi-file case.

Check verification status

action=checkverifystatus

guid is the value returned by verifysourcecode.

Params
Example Result

Parameter	Description
guid	`string` used for identifying the verification attempt

{
  "message": "OK",
  "result": "Pending in queue",
  "status": "1"
}

Return options: Pending in queue | Pass - Verified | Fail - Unable to verify | Unknown UID

cURL

curl "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=checkverifystatus&guid=<guid>&apikey=<your_pro_api_key>"

Verify a proxy contract

action=verifyproxycontract, checked with action=checkproxyverification Same route family as the actions above — pass the proxy’s own address and Blockscout resolves and links the implementation contract.

Params
Example Result

Parameter	Description
address	`string` containing the address hash of the proxy contract

{
  "message": "OK",
  "result": "c32d204404f33ff38fee42394f7e671fd96314b3658d466a",
  "status": "1"
}

Poll the result with action=checkproxyverification&guid=<guid>. Return options: Verification in progress | a success message naming the resolved implementation address | A corresponding implementation contract was unfortunately not detected for the proxy address. | Unknown UID

cURL

curl "https://api.blockscout.com/v2/api?chain_id=11155111&module=contract&action=verifyproxycontract&address=0xYourProxyAddress&apikey=<your_pro_api_key>"

Blockscout APIs

PRO API Endpoints

Additional Service APIs

Blockscout Smart Contract Verification API

License type

Via flattened source code or standard JSON input

Via Sourcify

Vyper contracts

Multiple raw source files

Check verification status

Verify a proxy contract

​License type

​Via flattened source code or standard JSON input

​Via Sourcify

​Vyper contracts

​Multiple raw source files

​Check verification status

​Verify a proxy contract

License type

Via flattened source code or standard JSON input

Via Sourcify

Vyper contracts

Multiple raw source files

Check verification status

Verify a proxy contract