OpenAPI payload validator

Validate a JSON payload against the request or response schema for one operation in an OpenAPI 3.x or Swagger 2.x spec. Locate the operation by operationId or method+path; choose `part: "request"` or `part: "response"` (status defaults to the first 2xx). Deterministic subset of JSON Schema: type, required, enum, properties, items, additionalProperties:false, oneOf/anyOf/allOf, $ref-detection (not dereferenced). Returns `valid`, `schemaPresent` (false → no contract to check; result is vacuously valid), and ordered `errors[]` with stable rule codes. Pure CPU — deterministic, no network.

Input

Field	Type	Description
spec *	any	OpenAPI/Swagger document (object or JSON string)
operationId	any	operationId to validate against (preferred)
method	any	HTTP method (use with `path` if no operationId)
path	any	Path template (use with `method` if no operationId)
part *	any	Schema to validate against: "request" or "response"
status	any	Response status when part="response" (defaults to first 2xx)
payload *	any	JSON value to validate

Example output

{
  "valid": false,
  "schemaPresent": true,
  "errors": [
    {
      "path": "",
      "rule": "required",
      "message": "missing required field: email"
    },
    {
      "path": ".age",
      "rule": "type",
      "message": "expected integer, got string"
    },
    {
      "path": ".extra",
      "rule": "additionalProperties",
      "message": "unexpected property: extra"
    }
  ]
}

Try it — see the 402 challenge (free)

curl -i -X POST https://agent402.tools/api/openapi-validate-payload \
  -H "Content-Type: application/json" \
  -d '{"spec":{"openapi":"3.0.0","paths":{"/users":{"post":{"operationId":"createUser","requestBody":{"content":{"application/json":{"schema":{"type":"object","required":["name","email"],"properties":{"name":{"type":"string"},"email":{"type":"string"},"age":{"type":"integer"},"role":{"type":"string","enum":["admin","user"]}},"additionalProperties":false}}}},"responses":{"201":{"description":"ok"}}}}}},"operationId":"createUser","part":"request","payload":{"name":"Alice","age":"thirty","extra":"noise"}}'

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-validate-payload", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "spec": {
      "openapi": "3.0.0",
      "paths": {
        "/users": {
          "post": {
            "operationId": "createUser",
            "requestBody": {
              "content": {
                "application/json": {
                  "schema": {
                    "type": "object",
                    "required": [
                      "name",
                      "email"
                    ],
                    "properties": {
                      "name": {
                        "type": "string"
                      },
                      "email": {
                        "type": "string"
                      },
                      "age": {
                        "type": "integer"
                      },
                      "role": {
                        "type": "string",
                        "enum": [
                          "admin",
                          "user"
                        ]
                      }
                    },
                    "additionalProperties": false
                  }
                }
              }
            },
            "responses": {
              "201": {
                "description": "ok"
              }
            }
          }
        }
      }
    },
    "operationId": "createUser",
    "part": "request",
    "payload": {
      "name": "Alice",
      "age": "thirty",
      "extra": "noise"
    }
  }),
});

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-validate-payload")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/openapi-validate-payload", { method: "POST", headers: { "X-Pow-Solution": c.token + ":" + n, "Content-Type": "application/json" }, body: JSON.stringify({"spec":{"openapi":"3.0.0","paths":{"/users":{"post":{"operationId":"createUser","requestBody":{"content":{"application/json":{"schema":{"type":"object","required":["name","email"],"properties":{"name":{"type":"string"},"email":{"type":"string"},"age":{"type":"integer"},"role":{"type":"string","enum":["admin","user"]}},"additionalProperties":false}}}},"responses":{"201":{"description":"ok"}}}}}},"operationId":"createUser","part":"request","payload":{"name":"Alice","age":"thirty","extra":"noise"}}) });

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