> ## 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.

# Wallet nonce management

<Note>
  **Note:** This topic applies to EVM blockchains only. For [Transactions
  V2](/cpn/concepts/transactions/transactions-v2), nonces are managed by CPN so
  you don't need to actively manage them.
</Note>

This topic explains how nonces work in Ethereum Virtual Machine (EVM)
transactions. It also gives you tips for managing nonces when you handle many
transactions at once.

Before you read this, you should know the basics about EVM wallets and how
transactions are signed.

## What is a nonce?

In EVM-based blockchains, a wallet nonce is a counter. It tracks how many
transactions you sent from a specific wallet address. Each transaction must use
a different nonce. You must use nonces in order, one after another.

Key points:

* New wallets start with nonce 0
* Each successful transaction adds 1 to the nonce
* You must use nonces in order (no gaps)
* Each wallet address has its own nonce count

## Nonce conflicts in concurrent transactions

Problems can happen when you create many transactions at the same time from one
wallet address.

This problem often happens when many users create transactions at once, and your
system uses the same EVM wallet for all these requests.

When signing transactions, multiple threads in your system might try to get the
wallet's current nonce at the same time. If this race condition occurs, multiple
transactions might get assigned the same nonce number. When this occurs, only
the first transaction works. The others fail.

Another common problem happens when transactions get stuck in the blockchain's
mempool and block later transactions. Here's an example:

* Your CPN integration signs two transactions from the same wallet in the right
  order:
  * Transaction A with nonce 5
  * Transaction B with nonce 6
* Transaction A gets rejected by CPN because it has the wrong parameters
* Transaction B goes to the blockchain but gets stuck in the mempool because the
  blockchain needs nonce 5 first
* All future transactions from this wallet get blocked until you fix the gap

## Best practices for managing nonces

Your integration may vary based on your systems. Here are some general tips for
managing nonces:

**Set up one central system to track nonces for each wallet.** This system
should safely handle nonce assignment when multiple threads request to sign
transactions at once. Make sure each nonce gets assigned only once to prevent
duplicates. You can use a locking system or a queue system to manage nonce
assignment when handling multiple operations.

**Keep your system in sync with the blockchain to track the latest nonce
numbers.** Your local nonce tracking should reset its counter if it gets out of
sync with the blockchain's nonce state. Set up regular health checks to find
nonce gaps.

You should sync with the blockchain:

* Before starting new transaction batches
* After transactions fail or get rejected
* When your systems restart after downtime