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Multi-chain block explorer queries via Etherscan V2 unified API + Foundry cast fallbacks. Look up contract ABI/source, transactions, receipts, event logs, balances, token info, contract creation, gas prices, verify contracts across Ethereum, BSC, Polygon, Arbitrum, Optimism, Base, Avalanche, Sepolia and 60+ other chains. One API key, one endpoint, any chain.
Passed 14 of 18 test cases with the skill, and 9 of 18 without it.
and 6 more in the full report
7 fixed10 passed either way4 still failing1 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 7 test cases the skill fixed. Same model, same prompt, with and without the skill.
Provide the terminal command to verify a contract named TokenVault deployed at 0x9999... on Ethereum Sepolia testnet using Foundry CLI.
| Checked | Without skill | With skill |
|---|---|---|
| Uses forge verify-contract | Passed | Passed |
| Passes --chain-id 11155111 | Missed | Passed |
The instructions your model reads when the skill loads.
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.
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
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.
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) |
test cases passed, vs 9 / 18 without
More skills from the same source and nearby in the registry, with their headline benchmark lift.