26 free, open-source blockchain developer tools that run 100% in your browser against live public RPCs and APIs. No backend, no accounts, no tracking.
Live: https://blockchains.github.io/blockchainlab-tools/
Built by Blockchain Lab — blockchainlab.com
| Tool | What it does |
|---|---|
| Safe multisig tx builder & decoder | Build a Safe transaction and compute its EIP-712 safeTxHash locally, cross-check against the Safe contract on-chain, read owners/threshold/nonce, and decode execTransaction or MultiSend batches. |
| EIP-712 signer / verifier | Hash EIP-712 typed data (digest, domain separator, struct hash), sign with a throwaway key or your wallet, recover the signer, verify personal_sign messages and check ERC-1271 smart-account signatures on-chain. |
| Calldata diff | Decode two calldata blobs (or two tx hashes) with openchain/4byte signatures and highlight every argument and 32-byte word that differs. |
| Contract verification lookup | Check whether a smart contract's source code is verified on Sourcify (full/partial match) and Blockscout, with compiler version, licence, proxy type and implementation addresses. |
| Gas history charts | Chart base fee, median priority tip and block fullness over the last 1,024 blocks for Ethereum, Base, Arbitrum, OP, Polygon, BNB Chain and Avalanche, with min/median/p75/max stats. |
| Bridge fee compare | Compare live quotes for bridging USDC or ETH between Ethereum, Base, Arbitrum, OP and Polygon: amount received, fees and estimated time from Across, LI.FI and Relay. |
| Token approval checker | Check which popular spenders (Permit2, Uniswap, 1inch, 0x, CoW, Balancer, OpenSea, Aave…) can move an address's ERC-20 tokens, flag unlimited approvals, and get one-click revoke links and approve(spender, 0) calldata. |
| ENS bulk resolver | Resolve a list of ENS names to addresses (with avatar, url, Twitter, GitHub records) and reverse-resolve addresses to primary names, verifying forward/reverse match. Export as CSV. |
| Solana tx decoder | Decode any Solana transaction signature: status, fee, compute units, parsed instructions and inner instructions with program names (Jupiter, Raydium, Orca, Meteora, SPL Token…), SOL and token balance changes, and logs. |
| Bitcoin PSBT decoder | Decode a Bitcoin PSBT (BIP-174, base64 or hex) or raw transaction: inputs, outputs, addresses, script types, fee and fee rate, signatures present, BIP-32 derivation paths. Runs offline in your browser. |
| Address labels | Look up public labels for an EVM address: Blockscout contract name and public tags, token info, ENS primary name, Uniswap token-list match, well-known spender names, and an OFAC SDN sanctions check. |
| Vanity address estimator | Estimate how many attempts and how long it takes to find an Ethereum vanity address prefix (case-insensitive or EIP-55 checksum), benchmarked live on your device, and compute CREATE2 deployment addresses. |
| Uniswap price impact | Quote a Uniswap v3 swap on-chain with QuoterV2 and see amount out, mid price, execution price, price impact, price after the trade, ticks crossed and gas estimate — Ethereum, Base, Arbitrum, OP, Polygon. |
| MEV sandwich checker | Paste an Ethereum/Base/Arbitrum/OP/Polygon transaction hash to check whether it was sandwiched: finds a front-run swap on the same pool in the same direction and a back-run reversing it from the same EOA or bot contract. |
| Stablecoin monitor | Live stablecoin table: price vs peg, circulating supply, 7-day supply change, peg mechanism and chain count for 400+ stablecoins from DefiLlama. |
| RPC health checker | Test free public RPC endpoints for Ethereum, Base, Arbitrum, OP, Polygon, BNB Chain and Avalanche from your browser: reachability, latency, chain ID and how many blocks behind the best endpoint each is. Plus the nightly server-side probe. |
| Tool | What it does |
|---|---|
| Gas & fee estimator | Live base fee / priority tips (eth_feeHistory) on Ethereum, Base, Arbitrum, OP, Polygon, BNB, Avalanche + Bitcoin sat/vB + Solana priority fees, with USD cost |
| Unit converter | wei/gwei/ether, sats/BTC, lamports/SOL with exact BigInt maths |
| ABI encoder/decoder | Encode calls, decode calldata, selectors/topics, unknown-selector lookup (openchain + 4byte) |
| Address & ENS | EIP-55 checksum, ENS forward/reverse, balance, nonce, contract detection, EIP-1967/zeppelinos proxy implementation, EIP-7702 delegation, ERC-20 metadata |
| Transaction decoder | Status, fees, L1 data fee, decoded function + args and event logs for any tx hash on 7 EVM chains |
| Hash & Merkle | keccak256/sha256/ripemd160; OpenZeppelin StandardMerkleTree / SimpleMerkleTree roots + proofs |
| Storage slots | Mapping / nested mapping / dynamic array / ERC-7201 / EIP-1967 slots, then read the live value |
| EIP/ERC/BIP reference | Search every EIP, ERC and BIP (rebuilt nightly from the official repos) |
| Chainlist | 2,700+ EVM chains from chainid.network, live RPC latency test, add-to-wallet |
| Token lookup | Uniswap default token list search + on-chain verification |
…/safe/?chain=ethereum&safe=0x…·…/verify/?chain=base&address=0x…·…/approvals/?address=vitalik.eth·…/mev/?chain=ethereum&hash=0x…·…/solana-tx/?sig=…·…/labels/?address=0x…
Deep links (used by blockchainlab-lens and the MCP server)
https://blockchains.github.io/blockchainlab-tools/tx/?chain=base&hash=0x…https://blockchains.github.io/blockchainlab-tools/address/?q=vitalik.eth&chain=ethereumhttps://blockchains.github.io/blockchainlab-tools/abi/?data=0xa9059cbb…https://blockchains.github.io/blockchainlab-tools/units/?v=1.5&u=ether·https://blockchains.github.io/blockchainlab-tools/reference/?q=4337·https://blockchains.github.io/blockchainlab-tools/chains/?q=8453
| Source | Used for |
|---|---|
| PublicNode RPCs (+ mainnet.base.org, arb1.arbitrum.io fallbacks) | gas, tx, address, storage, ERC-20 reads |
| mempool.space API | Bitcoin fee rates |
Solana RPC getRecentPrioritizationFees |
Solana priority fees |
| DefiLlama coins API | USD prices |
| openchain.xyz / 4byte.directory | function / event signatures |
| Blockchain Lab Open Data API | chains (chainid.network), EIPs/ERCs/BIPs |
| Uniswap token list | token lookup |
Caveats: L2 gas figures are execution fees only (rollups add an L1 data fee, shown per-tx in the decoder when the receipt reports it). Public RPCs are pruned — very old Ethereum history (pre-block ~15.5M) may be unavailable.
Everything is tested against live networks — no mocks:
npm install && npm test # Node: units, ABI, ENS, fees on 7 chains, real tx decoding, Merkle/ERC-7201 vectors, USDC storage slot == balanceOf
pip install playwright && python3 test/e2e.py # headless Chrome against the live Pages site, every toolWhat the suites check:
npm testrunstest/core.test.mjs(pack 1) andtest/core2.test.mjs(pack 2, 16 groups): Safe hash computed locally == the Safe's owngetTransactionHash()on a Safe freshly discovered from factory logs; EIP-712 spec "Mail" digest + signer vector; Sourcify/Blockscout verification of USDC; 1,024-block fee history; live Across/LI.FI/Relay quotes; Permit2 allowance via Multicall3 == directallowance(); ENS bulk; a live Jupiter Solana tx; the official BIP-174 PSBT vector + a self-built, signed P2WPKH tx; OFAC-list hit; EIP-1014 CREATE2 vector; Uniswap v3 QuoterV2 vsslot0; a real jaredfromsubway sandwich (block 26119673); DefiLlama stablecoins; public RPC health.python3 test/e2e.py [base]drives every page in headless Chrome (27 checks) — run daily in CI against the live Pages site.
CI runs both on every push and daily (live-tests.yml).
Plain HTML + ES modules, ethers v6 and @openzeppelin/merkle-tree via import map (CDN). python3 gen_pages.py regenerates the tool pages; shared logic lives in assets/core.js.
Open Data API · MCP server · Lens · Labs · Roadmap · Interview questions · Whitepaper library
MIT licensed. Not financial advice.
For AI agents and builders: read
AGENTS.md(setup, commands, structure, rules),llms.txt(doc map) and the machine-readableblocks.json(schema). How all Blockchains blocks fit together: Build with Blocks · org catalogue: https://blockchains.github.io/blocks.json.
What it exports
| Export | Type | Install / access |
|---|---|---|
tool deep links |
web | https://blockchains.github.io/blockchainlab-tools/tx/?chain=base&hash=0x… |
assets/core.js |
file | git clone + npm install, then import * as C from './assets/core.js' |
assets/core2.js |
file | assets/core2.js |
assets/core.js exports: convertUnits, selector, topic, encodeCall, decodeCalldata, decodeTx, evmFees, btcFees, solFees, resolveEns, reverseEns, addressInfo, erc20Meta, readSlot, mappingSlot, erc7201Slot, merkleStandard, merkleSimple, hashes, dataset, CHAINS
assets/core2.js exports: multicall, safeTxHash, safeInfo, decodeSafeCalldata, typedDataHash, recoverTypedData, erc1271, calldataDiff, verification, gasHistory, bridgeQuotes, approvals, ensBulk, decodeSolTx, decodePSBT, addressLabels, priceImpact, sandwichCheck, stablecoins, rpcHealth, create2Address
Minimal example (run on 2026-10-04 from a clone after npm install (Node 20))
// node --input-type=module, from the repo root
import * as C from "./assets/core.js";
C.convertUnits("1.5", "ether").wei; // "1500000000000000000"
C.selector("transfer(address,uint256)"); // "0xa9059cbb"
C.erc7201Slot("example.main"); // 0x183a6125…eab500 (ERC-7201 spec vector)
await C.evmFees("base"); // { chain, gasPriceWei, baseFeeWei, tipWei, oldestBlock }Inputs → outputs
- In:
query params(URL) chain, hash, address/q, data, v/u depending on the tool;function args(JS) addresses, hashes, calldata, chain keys - Out:
rendered tool page(HTML);JS results(objects) decoded calls, fees in wei/USD, slots, hashes
Composes with
- Blockchains/blockchainlab-mcp: the MCP server wraps the same logic as agent tools
- Blockchains/blockchainlab-lens: the extension opens these pages for explorer tx/address URLs
- Blockchains/blockchainlab-api: chains and EIP/ERC/BIP reference data
- Blockchains/blockchain-dev-roadmap: roadmap stages link to the tools
- Blockchains/blockchains.github.io: listed on the hub
Versioning & stability: stable. Deep-link URLs (/<tool>/?chain=…&hash=…) are treated as a stable interface (Lens and the MCP server depend on them). assets/core*.js is internal-but-reusable: no npm package, so vendor a pinned commit.
None. Every tool runs in the browser against public RPCs and public APIs; no keys, no backend.
Issues and pull requests are welcome. Please read the contributing guide, code of conduct and security policy first.
Built by Blockchain Lab — blockchainlab.com