Tools

A tool is an HTTPS endpoint you own, added on the agent's Tools tab. You give it a name and description (what the model sees), a JSON Schema for its input, and a service.operation that the policy decides on.

What Gasket sends#

POST https://your-api.com/gasket/lookup-order
Content-Type: application/json
Gasket-Signature: t=1760532068,v1=5f1c…
Gasket-Action: act_...

{
  "tool": "lookup_order",
  "input": { "order_id": "4821" },
  "run_id": "run_...",
  "action_id": "act_...",
  "agent_id": "agt_...",
  "environment": "test"
}

Return any 2xx with a body (JSON or text, up to 8 KB); it goes to the model as the tool result. Anything else, or no answer within 15 seconds, is reported to the model as a failure, and the action is recorded as failed.

Verify the signature#

Every tool request is signed with the agent's signing secret (shown on the Tools tab). Reject requests that don't verify.

import crypto from "node:crypto";

// header: the Gasket-Signature header, "t=<unix seconds>,v1=<hex>"
// body:   the raw request body, exactly as received
export function verifyGasket(header, body, secret) {
  const { t, v1 } = Object.fromEntries(header.split(",").map((p) => p.split("=")));
  if (!t || !v1 || Math.abs(Date.now() / 1000 - Number(t)) > 300) return false;
  const expected = crypto.createHmac("sha256", secret).update(`${t}.${body}`).digest("hex");
  return expected.length === v1.length && crypto.timingSafeEqual(Buffer.from(expected), Buffer.from(v1));
}

Rules for tool URLs#

• https:// only, on the default port.
• Must resolve to a public address (no localhost, private or internal networks).
• Redirects aren't followed.

Policy#

Each tool call becomes an action decided by the agent's policy before Gasket sends anything. Allowed: Gasket calls your endpoint. Denied: the model is told it was refused. Needs approval: the run pauses until a person decides.