Chainscan — Etherscan V2 unified explorer skill

Query any major EVM chain's block explorer via the Etherscan V2 unified API, with Foundry cast as a fallback for paid-tier endpoints. One Etherscan.io API key works across every supported chain through V2 — BscScan/PolygonScan/etc. keys do not work and are no longer needed.

> Etherscan V1 was deprecated 2025-08-15. V2 is the only API path going forward.

Configuration

Base URL:        https://api.etherscan.io/v2/api
API key:         {{vault:ETHERSCAN_API_KEY}}
Auth pattern:    &apikey={{vault:ETHERSCAN_API_KEY}}
Chain selector:  &chainid=<id>   (REQUIRED on every call — no default)
Free tier:       3 req/sec, 100k req/day

Chain ID quick reference

Most-used chains:

| Chain | chainid | Native | Default RPC | |---|---|---|---| | Ethereum mainnet | 1 | ETH | https://eth.llamarpc.com | | BSC | 56 | BNB | https://bsc-dataseed.binance.org | | Polygon | 137 | MATIC | https://polygon-rpc.com | | Arbitrum One | 42161 | ETH | https://arb1.arbitrum.io/rpc | | Optimism | 10 | ETH | https://mainnet.optimism.io | | Base | 8453 | ETH | https://mainnet.base.org | | Avalanche C-chain | 43114 | AVAX | https://api.avax.network/ext/bc/C/rpc | | Sepolia | 11155111 | ETH | https://ethereum-sepolia-rpc.publicnode.com | | Base Sepolia | 84532 | ETH | https://sepolia.base.org | | Arbitrum Sepolia | 421614 | ETH | https://sepolia-rollup.arbitrum.io/rpc |

Full list: see references/chains.md.

Free-tier endpoint availability

This is the most important table to internalize. Many endpoints are gated behind paid plans on non-Ethereum chains.

| Endpoint | ETH (1) | Polygon (137) | Arbitrum (42161) | BSC (56) | Base (8453) | OP (10) | Avalanche (43114) | |---|---|---|---|---|---|---|---| | getabi | YES | YES | YES | YES | YES | YES | YES | | getsourcecode | YES | YES | YES | YES | YES | YES | YES | | verifysourcecode | YES | YES | YES | YES | YES | YES | YES | | checkverifystatus | YES | YES | YES | YES | YES | YES | YES | | getcontractcreation | YES | YES | YES | NO | NO | NO | NO | | balance, txlist, tokentx, getLogs, gas, prices | YES | YES | YES | NO | NO | NO | NO |

Bolded YES = available on all plans including free for that chain. So contract ABI/source and verification work everywhere; everything else needs cast on paid chains.

Etherscan V2 endpoints

Every URL adds &chainid=<CHAIN>&apikey={{vault:ETHERSCAN_API_KEY}}. Replace <CHAIN> with the chain ID from the table above.

Contract ABI

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=contract&action=getabi&address=<ADDR>&apikey={{vault:ETHERSCAN_API_KEY}}" | python3 -m json.tool

Returns result as a JSON-stringified ABI array. Pipe through python3 -c 'import sys,json; print(json.dumps(json.loads(json.load(sys.stdin)["result"]), indent=2))' to fully decode.

Verified source code

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=contract&action=getsourcecode&address=<ADDR>&apikey={{vault:ETHERSCAN_API_KEY}}" | python3 -m json.tool

Returns: SourceCode, ABI, ContractName, CompilerVersion, OptimizationUsed, Runs, ConstructorArguments, LicenseType, Proxy, Implementation. For proxies, the returned ABI is the proxy's; fetch Implementation separately for the impl ABI.

Contract creation tx (creator + creation hash)

Free on Ethereum/Polygon/Arbitrum, paid elsewhere. Max 5 addresses per call (comma-separated).

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=contract&action=getcontractcreation&contractaddresses=<ADDR1>,<ADDR2>&apikey={{vault:ETHERSCAN_API_KEY}}" | python3 -m json.tool

For paid chains, fall back to a binary-search using cast code. See "Find deployment block" below.

Transaction by hash

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=proxy&action=eth_getTransactionByHash&txhash=<TXHASH>&apikey={{vault:ETHERSCAN_API_KEY}}" | python3 -m json.tool

> The proxy module returns raw JSON-RPC shape {jsonrpc, id, result}, not the standard {status, message, result} wrapper. Handle both shapes when parsing.

Transaction receipt (logs, status)

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=proxy&action=eth_getTransactionReceipt&txhash=<TXHASH>&apikey={{vault:ETHERSCAN_API_KEY}}" | python3 -m json.tool

Event logs

Free on Ethereum/Polygon/Arbitrum, paid elsewhere.

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=logs&action=getLogs&address=<ADDR>&fromBlock=<FROM>&toBlock=<TO>&topic0=<HASH>&apikey={{vault:ETHERSCAN_API_KEY}}" | python3 -m json.tool

Pagination: &page=1&offset=1000. Multiple topics: topic1, topic2, topic3, with topic0_1_opr=and|or for combinators.

> Effective 2026-07-01, free-tier getLogs and txlist max records drop from 10,000 to 1,000 per request. Paginate.

Native balance

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=account&action=balance&address=<ADDR>&tag=latest&apikey={{vault:ETHERSCAN_API_KEY}}"

Returns wei as a string. Multi-address: action=balancemulti&address=<ADDR1>,<ADDR2> (max 20).

ERC-20 token balance

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=account&action=tokenbalance&contractaddress=<TOKEN>&address=<HOLDER>&tag=latest&apikey={{vault:ETHERSCAN_API_KEY}}"

Returns raw integer (no decimals applied). Fetch decimals() separately to format.

Normal txs for an address

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=account&action=txlist&address=<ADDR>&startblock=0&endblock=99999999&page=1&offset=100&sort=desc&apikey={{vault:ETHERSCAN_API_KEY}}" | python3 -m json.tool

Use action=tokentx for ERC-20 transfers, action=tokennfttx for NFTs.

Verify contract source (POST)

bash
curl -s -X POST "https://api.etherscan.io/v2/api" \
  -d "chainid=<CHAIN>" \
  -d "module=contract" \
  -d "action=verifysourcecode" \
  -d "apikey={{vault:ETHERSCAN_API_KEY}}" \
  -d "contractaddress=<ADDR>" \
  -d "sourceCode=<STANDARD_JSON_INPUT>" \
  -d "codeformat=solidity-standard-json-input" \
  -d "contractname=<File.sol>:<ContractName>" \
  -d "compilerversion=v0.8.26+commit.8a97fa7a" \
  -d "optimizationUsed=1" \
  -d "runs=200" \
  -d "constructorArguements=<ABI_ENCODED_ARGS>" \
  -d "licenseType=3"

License IDs: 1=No License, 2=Unlicense, 3=MIT, 4=GPL-2.0, 5=GPL-3.0, 6=LGPL-2.1, 7=LGPL-3.0, 8=BSD-2-Clause, 9=BSD-3-Clause, 10=MPL-2.0, 11=OSL-3.0, 12=Apache-2.0, 13=AGPL-3.0, 14=BUSL-1.1.

Check verification status

bash
curl -s "https://api.etherscan.io/v2/api?chainid=<CHAIN>&module=contract&action=checkverifystatus&guid=<GUID>&apikey={{vault:ETHERSCAN_API_KEY}}"

Verify with Forge (preferred)

bash
forge verify-contract <ADDR> <ContractName> \
  --chain-id <CHAIN> \
  --etherscan-api-key {{vault:ETHERSCAN_API_KEY}} \
  --watch

Forge handles the V2 endpoint URL automatically.

Foundry cast fallbacks (for paid endpoints)

Use these when the chain isn't on the free tier (BSC, Base, OP, Avalanche, etc.). Pass --rpc-url <RPC> from the chain table.

bash
# Native balance
cast balance <ADDR> --rpc-url <RPC> --ether

# Contract code (existence check)
cast code <ADDR> --rpc-url <RPC> | head -c 80     # "0x" if no contract

# Tx + receipt
cast tx <TXHASH> --rpc-url <RPC>
cast receipt <TXHASH> --rpc-url <RPC>

# Block / chain state
cast block-number --rpc-url <RPC>
cast block <BLOCK> --rpc-url <RPC>
cast gas-price --rpc-url <RPC>
cast nonce <ADDR> --rpc-url <RPC>

# Storage slot
cast storage <ADDR> <SLOT> --rpc-url <RPC>

# Read calls
cast call <ADDR> "name()(string)" --rpc-url <RPC>
cast call <ADDR> "balanceOf(address)(uint256)" <HOLDER> --rpc-url <RPC>

# Event logs (raw)
cast logs --from-block <FROM> --to-block <TO> \
  --address <ADDR> "Transfer(address,address,uint256)" \
  --rpc-url <RPC>

# By topic hash
cast logs --from-block <FROM> --to-block <TO> \
  --address <ADDR> --topic0 <HASH> --rpc-url <RPC>

# Decoders / encoders
cast 4byte-decode 0x<METHOD_ID>          # selector → signature
cast calldata-decode "fn(types)" 0x<DATA>
cast sig "transfer(address,uint256)"     # signature → selector
cast keccak "Transfer(address,address,uint256)"  # event topic

# Unit conversions
cast to-wei 1.5 ether
cast from-wei <WEI>
cast to-hex <DEC>
cast to-dec 0x<HEX>

Find contract deployment block (binary search)

When getcontractcreation is paid on the chain, binary-search with cast code:

bash
# Returns "0x" if not deployed at <BLOCK>, else has bytecode
cast code <ADDR> --block <BLOCK> --rpc-url <RPC> | head -c 10

Algorithm: midpoint check, halve range based on whether code exists, until you converge to the exact deployment block. ~25 calls for any block range up to current head.

Critical gotchas

1. status === "1" (string) — V2 returns success as "1" not 1 and not true. Bad calls return HTTP 200 with {"status":"0","message":"NOTOK","result":"..."}. Always check status === "1", never truthy result.
2. chainid is required. Missing it returns an error, not a default-to-Ethereum.
3. Old chain-specific keys (BscScan, PolygonScan) don't work on V2. Must be an Etherscan.io key.
4. proxy module returns raw JSON-RPC shape {jsonrpc, id, result}, not the standard wrapper. Other modules return {status, message, result}.
5. getsourcecode proxies: check the Proxy ("1"/"0") and Implementation fields. For proxies the returned ABI is the proxy's, not the impl's.
6. getcontractcreation caps at 5 addresses per call. Batch larger lookups.
7. tokenbalance returns raw integer. Always fetch decimals() to format.
8. Rate limits: 3 req/sec, 100k/day on free. Space rapid-fire calls or you'll start getting Max calls per sec rate limit reached strings in result.
9. getLogs/txlist 10k → 1k pagination cap effective 2026-07-01. Paginate now, future-self thanks you.
10. Native-currency price endpoints (bnbprice, ethprice, etc.) are paid on most chains. Use CoinGecko (api.coingecko.com/api/v3/simple/price) for free.

Decision flow

When the user asks for chain data:

1. Need ABI or source? → Etherscan V2 (free on every chain).
2. Need a tx, receipt, balance, log, or read call? → if chain ∈ {ETH, Polygon, Arbitrum}, use V2; else use cast with the RPC.
3. Verifying a contract? → forge verify-contract is the easiest path, V2 POST is the manual fallback.
4. Paid endpoint on a paid chain? → use cast (free, fast, no rate limit beyond RPC).
5. Native price? → CoinGecko, not the explorer.

References

• references/chains.md — complete chain ID + RPC inventory (60+ chains).
• references/endpoints.md — every V2 endpoint with full parameter list.

Notes

• The same Etherscan.io key in this skill is also referenced by ~/.claude/skills/bscscan/SKILL.md. They share the key intentionally — V2 unified everything, so one key serves both skills. The bscscan skill is BSC-specific; this chainscan skill is the general multi-chain version.