> ## Documentation Index
> Fetch the complete documentation index at: https://developers.circle.com/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}.
> Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts.
> Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md.
> Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md.
> Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.
> Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.
> Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming.
> Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md.
> Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors.
> API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.
> Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes.
> When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records.
> Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md.

# EVM testnet chain IDs for signing

> Chain IDs supported by EVM testnet wallets for signing transactions.

`EVM-TESTNET` wallets support signing on the blockchains listed below. For
mainnet `EVM` wallets, you can sign on any EVM-compatible blockchain using its
standard chain ID. Find chain IDs at [chainlist.org](https://chainlist.org).

<Note>
  This list covers blockchains outside Circle's natively supported testnets.
  Circle-supported testnets such as Arc Testnet use their own chain codes and
  are listed in [Supported blockchains](/wallets/supported-blockchains). They do
  not require an `EVM-TESTNET` wallet.
</Note>

For instructions on how to sign transactions, see
[Sign Transactions on EVM Chains](/wallets/sign-tx-evm).

| Chain ID | Blockchain |
| - | - |
| 9 | Ubiq Network Testnet |
| 16 | Flare Testnet Coston |
| 18 | ThunderCore Testnet |
| 21 | Elastos Smart Chain Testnet |
| 31 | Rootstock Testnet |
| 41 | Telos EVM Testnet |
| 43 | Darwinia Pangolin Testnet |
| 45 | Darwinia Pangoro Testnet |
| 65 | OKExChain Testnet |
| 69 | Optimism Kovan |
| 83 | Meter Testnet |
| 97 | BNB Smart Chain Testnet |
| 114 | Flare Testnet Coston2 |
| 120 | ENULS Testnet |
| 123 | Fuse Sparknet |
| 155 | Tenet Testnet |
| 170 | HOO Smart Chain Testnet |
| 226 | LACHAIN Testnet |
| 296 | Hedera Testnet |
| 322 | KCC Testnet |
| 335 | DFK Chain Test |
| 338 | Cronos Testnet |
| 363 | Theta Sapphire Testnet |
| 364 | Theta Amber Testnet |
| 365 | Theta Testnet |
| 568 | Dogechain Testnet |
| 588 | Metis Stardust Testnet |
| 647 | SX Network Testnet |
| 740 | Canto Testnet |
| 919 | Mode Testnet |
| 940 | PulseChain Testnet |
| 941 | PulseChain Testnet v2b |
| 942 | PulseChain Testnet v3 |
| 943 | PulseChain Testnet v4 |
| 999 | Wanchain Testnet |
| 1007 | Newton Testnet |
| 1028 | BitTorrent Chain Testnet |
| 1112 | WEMIX3.0 Testnet |
| 1115 | Core Blockchain Testnet |
| 1230 | Ultron Testnet |
| 1338 | Elysium Testnet |
| 1402 | Polygon zkEVM Testnet old |
| 1422 | Polygon zkEVM Testnet Pre Audit-Upgraded |
| 1442 | Polygon zkEVM Testnet |
| 1686 | Mint Testnet |
| 1819 | Cube Chain Testnet |
| 1891 | Lightlink Pegasus Testnet |
| 1945 | ONUS Chain Testnet |
| 2153 | Findora Testnet |
| 2154 | Findora Forge |
| 2221 | Kava Testnet |
| 2358 | Kroma Sepolia |
| 2522 | Fraxtal Testnet |
| 3141 | Filecoin - Hyperspace testnet |
| 4002 | Fantom Testnet |
| 4062 | Nahmii 3 Testnet |
| 4202 | Lisk Sepolia Testnet |
| 4690 | IoTeX Network Testnet |
| 5001 | Mantle Testnet |
| 5003 | Mantle Sepolia Testnet |
| 5553 | Nahmii Testnet |
| 5611 | opBNB Testnet |
| 5700 | Syscoin Tanenbaum Testnet |
| 5851 | Ontology Testnet |
| 7001 | ZetaChain Athens 3 Testnet |
| 7701 | Canto Tesnet |
| 7771 | Bitrock Testnet |
| 9000 | Evmos Testnet |
| 9527 | Rangers Protocol Testnet Robin |
| 9728 | Boba BNB Testnet |
| 10200 | Gnosis Chiado Testnet |
| 12345 | Step Testnet |
| 13337 | Beam Testnet |
| 20729 | Callisto Testnet |
| 22040 | AirDAO Testnet |
| 23888 | Blast Testnet |
| 31337 | GoChain Testnet |
| 31415 | Filecoin - Wallaby testnet |
| 43113 | Avalanche Fuji Testnet |
| 43851 | ZKFair Testnet |
| 44787 | Celo Alfajores Testnet |
| 46688 | Fusion Testnet |
| 49797 | Energi Testnet |
| 54211 | Haqq Chain Testnet |
| 55556 | REI Chain Testnet |
| 57000 | Rollux Testnet |
| 59140 | Linea Testnet |
| 62320 | Celo Baklava Testnet |
| 71401 | Godwoken Testnet v1 |
| 80002 | Amoy |
| 84532 | Base Sepolia Testnet |
| 88880 | Chiliz Scoville Testnet |
| 128123 | Etherlink Testnet |
| 167004 | Taiko (Alpha-2 Testnet) |
| 314159 | Filecoin - Calibration testnet |
| 333888 | Polis Testnet |
| 421614 | Arbitrum Sepolia |
| 432201 | Dexalot Subnet Testnet |
| 534351 | Scroll Sepolia Testnet |
| 534353 | Scroll Alpha Testnet |
| 534354 | Scroll Pre-Alpha Testnet |
| 666888 | Hela Official Runtime Testnet |
| 723107 | TixChain Avalanche Subnet |
| 3141592 | Filecoin - Butterfly testnet |
| 3441005 | Manta Pacific Testnet |
| 5201420 | Electroneum Testnet |
| 11155111 | Sepolia |
| 11155420 | OP Sepolia Testnet |
| 28122024 | Ancient8 Testnet |
| 31415926 | Filecoin - Local testnet |
| 168587773 | Blast Sepolia Testnet |
| 245022926 | Neon EVM Devnet |
| 245022940 | Neon EVM TestNet |
| 999999999 | Zora Sepolia Testnet |
| 1313161555 | Aurora Testnet |
| 1666700000 | Harmony Testnet Shard 0 |
| 1666700001 | Harmony Testnet Shard 1 |
| 1666900000 | Harmony Devnet Shard 0 |
| 1666900001 | Harmony Devnet Shard 1 |
| 11297108099 | Palm Testnet |