Memory compare-and-set

Atomically write (or release) a key only if its current value equals `expected` - the coordination primitive for distributed locks and optimistic concurrency across agents. Send POST /api/memory/cas with the required field key and pay $0.001 per call over x402 with USDC on an EVM chain (the paying wallet is the identity). It returns a JSON object with key, swapped, value, owner and expiresAt.

Acquire a lock: expected=null + a value + ttlSeconds. Release it: expected=<your token> with no value (deletes on match). Update safely: expected=<old>, value=<new>. Returns whether it swapped and the current value.

Category: Agent memory & coordination · Tags: memory cas compare-and-set lock coordination atomic · Also found as: memory-compare-and-set compare-and-set

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/memory/cas \
  -H "Content-Type: application/json" \
  -d '{"key":"locks/import","expected":null,"value":"agent-7","ttlSeconds":30}'

Without payment this returns HTTP 402 Payment Required with the exact price for memory-cas; any x402 v2 or MPP client pays it and retries.

Example response

{
  "key": "locks/import",
  "swapped": true,
  "value": "agent-7",
  "owner": "0x…",
  "expiresAt": 1760086430
}

From an MCP client

catalog.call {
  "slug": "memory-cas",
  "params": {
    "key": "locks/import",
    "expected": null,
    "value": "agent-7",
    "ttlSeconds": 30
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for memory-cas; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY (wallet only for this tool). Local install: npx -y agent402-mcp.

Errors and behavior

• key is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402 or MPP: settlement is cancelled when the tool fails.
• Wallet-only: this tool reaches the network or stored state, so it has no proof-of-work tier.
• Identity-bound: results are keyed to the wallet that signed the payment, so only EVM x402 payments are accepted; credits keys and Tempo are refused.
• A GET or HEAD to /api/memory/cas returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/memory/cas", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "key": "locks/import",
    "expected": null,
    "value": "agent-7",
    "ttlSeconds": 30
  }),
});

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