walletcap

One cap across Coinbase Spend Permissions

You let an agent pull USDC from a Coinbase Smart Wallet with Spend Permissions, and you want one daily limit for the agent however many permissions it holds. Spend Permissions count each allowance per permission and per fixed period, so a second permission, or two payments either side of a period boundary, can pass the daily budget you meant. AccountCapSpender is a spender contract that counts every payment through it, from every permission that names it, against one rolling window.

Unaudited. Testnet only. AccountCapSpender moves real tokens on behalf of an agent and has not had an independent audit. Read solidity/README.md before deploying it, and don’t point it at a mainnet SpendPermissionManager until an audit is complete.

Deploy it on a testnet

$ cd solidity
$ forge create src/AccountCapSpender.sol:AccountCapSpender \
    --rpc-url "$BASE_SEPOLIA_RPC_URL" \
    --private-key "$DEPLOYER_KEY" \
    --constructor-args \
      "$SPEND_PERMISSION_MANAGER" \
      "$AGENT" \
      "$CAP_IN_ATOMIC_UNITS" \
      "$WINDOW_SECONDS" \
      "$PER_PAYMENT_IN_ATOMIC_UNITS" \
      "[\"$PAYEE\"]"

• The constructor takes the SpendPermissionManager, the agent, the cap, the rolling window in seconds (a multiple of 24), the per-payment max and the allowlisted payees. Use the SpendPermissionManager address Coinbase publishes for your chain.
• The account grants its Spend Permissions to the contract instead of the agent. The agent calls pay(permission, amount, payee), and every permission the account grants the contract shares one rolling cap.
• Only the agent may call pay, only to an allowlisted payee, at most the per-payment max at a time.
• The window is counted in 24 buckets, so every payment costs the same gas however many came before it. A payment counts for up to one bucket (window/24) past its window, never less.

The contract’s checks also run without Foundry, on an in-process EVM:

$ cd solidity/evm && npm install && node check.mjs ..

Crash test: $150 over with a second permission, $0 through AccountCapSpender

npx walletcap-crash-test runs Coinbase’s SpendPermissionManager v1.0.0 and Smart Wallet on an in-process EVM, from the runtime code deployed on Base mainnet. A Smart Wallet holds $1,000 of a test token that stands in for USDC, and grants the agent permissions of $150 a day. On walletcap’s side, the wallet grants the same permissions to AccountCapSpender.

Event	SpendPermissionManager	AccountCapSpender
a second permission	$300 pulled · $150 over	$150 pulled · $0 over
across a period boundary, 1 second apart	$300 pulled · $150 over	$150 pulled · $0 over

The result was the same in all eight runs on 6 November 2026. Within one permission and one period the manager holds: the crash test’s suite checks that a fourth $50 is refused with ExceededSpendPermission. AccountCapSpender refuses the second $150 with OverBudget.

Links

• README: Coinbase Spend Permissions, on chain
• The contract, its Foundry tests and the audit scope
• The crash test, which says exactly what runs, and all pages
• Off chain, the same budget idea for x402 payments: any x402 client and Coinbase CDP x402 spend controls

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