OpenAPI mock response generator

Synthesize a JSON response body for one operation + status code in an OpenAPI 3.x or Swagger 2.x spec. Locate the operation by operationId or method+path. Pick the response by explicit `status`, else the first 2xx, else the first documented response. Generation precedence: operation-level `example`/`examples` > schema `example` > recursive type-inferred walk (objects walk properties, arrays return [mock(items)], enums return the first value, $ref is surfaced literally). Returns a `source` tag so callers know the mock's fidelity. Pure CPU — deterministic, no network, no $ref dereferencing.

Input

Field	Type	Description
spec *	any	OpenAPI/Swagger document (object or JSON string)
operationId	any	operationId to mock (preferred)
method	any	HTTP method (use with `path` if no operationId)
path	any	Path template (use with `method` if no operationId)
status	any	Response status to mock (defaults to first 2xx)

Example output

{
  "status": "200",
  "contentType": "application/json",
  "mock": {
    "id": "u_42",
    "name": "Alice",
    "active": true,
    "roles": [
      "admin"
    ]
  },
  "source": "generated"
}

Try it — see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/openapi-mock-response \
  -H "Content-Type: application/json" \
  -d '{"spec":{"openapi":"3.0.0","paths":{"/users/{id}":{"get":{"operationId":"getUser","responses":{"200":{"description":"ok","content":{"application/json":{"schema":{"type":"object","properties":{"id":{"type":"string","example":"u_42"},"name":{"type":"string","example":"Alice"},"active":{"type":"boolean","example":true},"roles":{"type":"array","items":{"type":"string","example":"admin"}}}}}}}}}}}},"operationId":"getUser"}'

The response is HTTP 402 Payment Required with exact payment requirements. Any x402 v2 client pays automatically and retries:

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();
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/openapi-mock-response", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "spec": {
      "openapi": "3.0.0",
      "paths": {
        "/users/{id}": {
          "get": {
            "operationId": "getUser",
            "responses": {
              "200": {
                "description": "ok",
                "content": {
                  "application/json": {
                    "schema": {
                      "type": "object",
                      "properties": {
                        "id": {
                          "type": "string",
                          "example": "u_42"
                        },
                        "name": {
                          "type": "string",
                          "example": "Alice"
                        },
                        "active": {
                          "type": "boolean",
                          "example": true
                        },
                        "roles": {
                          "type": "array",
                          "items": {
                            "type": "string",
                            "example": "admin"
                          }
                        }
                      }
                    }
                  }
                }
              }
            }
          }
        }
      }
    },
    "operationId": "getUser"
  }),
});

No wallet? Pay with compute

This is a pure-CPU tool, so an agent without a wallet can pay with proof-of-work instead of USDC: fetch a challenge, solve the sha256 puzzle (16 leading zero bits — a fraction of a second of CPU, no money, no AI tokens), and resend with the X-Pow-Solution header.

import { createHash } from "node:crypto";
const lz = (b) => { let t = 0; for (const x of b) { if (!x) { t += 8; continue; } t += Math.clz32(x) - 24; break; } return t; };
const c = await (await fetch("https://agent402.tools/api/pow/challenge?slug=openapi-mock-response")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/openapi-mock-response", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"spec":{"openapi":"3.0.0","paths":{"/users/{id}":{"get":{"operationId":"getUser","responses":{"200":{"description":"ok","content":{"application/json":{"schema":{"type":"object","properties":{"id":{"type":"string","example":"u_42"},"name":{"type":"string","example":"Alice"},"active":{"type":"boolean","example":true},"roles":{"type":"array","items":{"type":"string","example":"admin"}}}}}}}}}}}},"operationId":"getUser"}) });

Related tools