API wallets and agents
An API wallet is a key the master account approves to sign trades for it: it can place and cancel orders but cannot withdraw or send funds to another address.
An API wallet, also called an agent, limits what a stolen trading key can do. Your bot’s key sits on a server, and if it were your account key a breach would drain the account. An agent is a second key your cold master approves: it signs orders and cancels but can’t move money to another address.
Say your account holds 50,000 USDC and the bot’s server is breached. The thief can lose that 50,000 through bad trades, but can’t withdraw it or send it to another address.
What an agent can sign, and what only the master can
Section titled “What an agent can sign, and what only the master can”The master signs approveAgent naming the agent’s address and an optional name. The agent then signs L1 actions for the master and its sub-accounts, only on the network hyperliquidChain binds: a testnet approval does nothing on mainnet.
| Who can sign | Actions |
|---|---|
| An agent (L1 actions) | orders, cancels, modifies, scheduleCancel, vault transfers, borrowLend, agentSetAbstraction, HIP-3 and HIP-4 deployer actions such as settlements, and agentSendAsset, between the account’s own balances only (destination must equal source) |
| The master key only (user-signed) | withdrawals (withdraw3), sends to another address (usdSend, spotSend, sendAsset), approving another agent, approving a builder fee |
| Never an agent, even an approved one | activateOutcomeDeployer |
An agent is a signer, not an account: queries on its address return empty (nonces and agents).
Slots, expiry and removal
Section titled “Slots, expiry and removal”Slots. One unnamed slot, several named ones; approving into an occupied slot or name replaces the holder. A valid_until <timestamp in milliseconds> suffix on the name sets an expiry, at most 180 days ahead.
Removal. There is no revoke action. Per the docs an agent is removed, and its nonce state may be pruned, when replaced, when expired, or when the registering account has no funds. In each case the re-approval danger below applies.
The numbers
Section titled “The numbers”| Item | Value | Source |
|---|---|---|
| Unnamed agents per account | 1 | exchange endpoint docs |
| Named agents per account | up to 3, plus 2 per sub-account | exchange endpoint docs |
| API wallets per account | 3 per master, plus 2 per sub-account | sub-accounts docs |
| Observed on one live account | 14 | measured; unreconciled with either figure |
| Longest expiry | 180 days | exchange endpoint docs |
| Agent name length | 1 to 16 characters | SDK constants |
| Nonces kept per signer | the 100 highest | nonce docs |
| Nonce window | block time minus 2 days to block time plus 1 day | nonce docs |
The count is unresolved: read extraAgents on your own account.
Keeping a trading key safe
Section titled “Keeping a trading key safe”- Retire a leaked key by approving a fresh address into its slot or name. Until then it trades without limit.
- Set a
valid_untilexpiry so a forgotten agent stops on its own. - Run one agent per process. Nonces are per signer, so processes sharing one collide. The docs recommend one API wallet per trading process and per sub-account.
Approving and inspecting agents from code
Section titled “Approving and inspecting agents from code”The master key signs the approval; a null agentName signs as the empty string and approves the unnamed agent.
{ "type": "approveAgent", "hyperliquidChain": "Mainnet", "signatureChainId": "0xa4b1", "agentAddress": "0x...", "agentName": "mm-1 valid_until 1767225600000", "nonce": 1760000000000}- Listing:
extraAgentsreturns{address, name, validUntil}entries, ornull(not an empty list) when there are none. - Identifying:
userRolereturns{"role": "agent", "data": {"user": "0x..."}}, naming the master. - From a contract: CoreWriter action 9,
(address wallet, string name), approves an API wallet for the contract’s own account; an empty name makes it the main agent. An off-chain keeper can then do what CoreWriter is not proven to carry, such as a borrow. - CoreWriter acts for the sender: an agent’s key calling CoreWriter acts for the agent’s own address, not its master.
- Multi-sig: the submitting leader can be an authorised user’s API wallet; its nonce is the one checked (multi-sig).
- Builder fees: an app can’t approve its own builder fee through a user’s agent (builder codes).
- Unknown signer: an unapproved or replaced agent, or a malformed signature, fails with
User or API Wallet ... does not exist, naming the recovered address (debugging).
For signing and replay protection in depth, see Nonces, expiry and API wallets. For L1 versus user-signed actions, see Signing from first principles.