OpenAPI required-params extractor

For one operation, return the minimum set of inputs an agent must provide to make a successful call. Send POST /api/openapi-required-params with the required field spec and pay $0.002 per call over x402 or MPP, or call it free by solving a proof-of-work challenge. It returns a JSON object with method, path, operationId, required, hasBody and 1 more.

Locate the op by `operationId` (preferred) or by `method`+`path`. Output is a single flat array tagged by `in`: `path` (always required), `query` / `header` / `cookie` (only when `required: true`), and `body.field` entries naming the top-level required fields of a required JSON request body. `hasBody` and `bodyContentType` are included separately so callers can decide whether to serialize a payload at all. Merges path-item-level shared parameters with operation-level ones (operation wins on collision), matching openapi-to-curl behavior. Does NOT recurse into nested object schemas - top-level required fields only. Pure CPU.

Category: Data conversion · Tags: openapi swagger required params api

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/openapi-required-params \
  -H "Content-Type: application/json" \
  -d '{"spec":{"openapi":"3.0.0","paths":{"/users/{id}":{"get":{"operationId":"getUser","parameters":[{"name":"id","in":"path","required":true,"schema":{"type":"string"}},{"name":"verbose","in":"query","required":false,"schema":{"type":"boolean"}},{"name":"X-Trace-Id","in":"header","required":true,"schema":{"type":"string"}}],"responses":{"200":{}}}},"/users":{"post":{"operationId":"createUser","requestBody":{"required":true,"content":{"application/json":{"schema":{"type":"object","required":["email","password"],"properties":{"email":{"type":"string"},"password":{"type":"string"},"nickname":{"type":"string"}}}}}},"responses":{"201":{}}}}}},"operationId":"createUser"}'

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

Example response

{
  "method": "POST",
  "path": "/users",
  "operationId": "createUser",
  "required": [
    {
      "in": "body.field",
      "name": "email",
      "type": "string"
    },
    {
      "in": "body.field",
      "name": "password",
      "type": "string"
    }
  ],
  "hasBody": true,
  "bodyContentType": "application/json"
}

From an MCP client

catalog.call {
  "slug": "openapi-required-params",
  "params": {
    "spec": {
      "openapi": "3.0.0",
      "paths": {
        "/users/{id}": {
          "get": {
            "operationId": "getUser",
            "parameters": [
              {
                "name": "id",
                "in": "path",
                "required": true,
                "schema": {
                  "type": "string"
                }
              },
              {
                "name": "verbose",
                "in": "query",
                "required": false,
                "schema": {
                  "type": "boolean"
                }
              },
              {
                "name": "X-Trace-Id",
                "in": "header",
                "required": true,
                "schema": {
                  "type": "string"
                }
              }
            ],
            "responses": {
              "200": {}
            }
          }
        },
        "/users": {
          "post": {
            "operationId": "createUser",
            "requestBody": {
              "required": true,
              "content": {
                "application/json": {
                  "schema": {
                    "type": "object",
                    "required": [
                      "email",
                      "password"
                    ],
                    "properties": {
                      "email": {
                        "type": "string"
                      },
                      "password": {
                        "type": "string"
                      },
                      "nickname": {
                        "type": "string"
                      }
                    }
                  }
                }
              }
            },
            "responses": {
              "201": {}
            }
          }
        }
      }
    },
    "operationId": "createUser"
  }
}

On the hosted connector at https://agent402.tools/mcp, catalog.call runs openapi-required-params free (rate-limited, no wallet). Local install: npx -y agent402-mcp.

Errors and behavior

• spec 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, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Free tier: no outbound network call leaves the server for this tool, so proof-of-work (16 leading zero bits of sha256) pays for it.
• A GET or HEAD to /api/openapi-required-params 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/openapi-required-params", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "spec": {
      "openapi": "3.0.0",
      "paths": {
        "/users/{id}": {
          "get": {
            "operationId": "getUser",
            "parameters": [
              {
                "name": "id",
                "in": "path",
                "required": true,
                "schema": {
                  "type": "string"
                }
              },
              {
                "name": "verbose",
                "in": "query",
                "required": false,
                "schema": {
                  "type": "boolean"
                }
              },
              {
                "name": "X-Trace-Id",
                "in": "header",
                "required": true,
                "schema": {
                  "type": "string"
                }
              }
            ],
            "responses": {
              "200": {}
            }
          }
        },
        "/users": {
          "post": {
            "operationId": "createUser",
            "requestBody": {
              "required": true,
              "content": {
                "application/json": {
                  "schema": {
                    "type": "object",
                    "required": [
                      "email",
                      "password"
                    ],
                    "properties": {
                      "email": {
                        "type": "string"
                      },
                      "password": {
                        "type": "string"
                      },
                      "nickname": {
                        "type": "string"
                      }
                    }
                  }
                }
              }
            },
            "responses": {
              "201": {}
            }
          }
        }
      }
    },
    "operationId": "createUser"
  }),
});

No wallet? Pay with compute

Fetch a challenge, solve the sha256 puzzle (16 leading zero bits, a fraction of a second of CPU), 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-required-params")).json();
let n = 0;
while (lz(createHash("sha256").update(c.challenge + ":" + n).digest()) < c.difficulty) n++;
await fetch("https://agent402.tools/api/openapi-required-params", { 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","parameters":[{"name":"id","in":"path","required":true,"schema":{"type":"string"}},{"name":"verbose","in":"query","required":false,"schema":{"type":"boolean"}},{"name":"X-Trace-Id","in":"header","required":true,"schema":{"type":"string"}}],"responses":{"200":{}}}},"/users":{"post":{"operationId":"createUser","requestBody":{"required":true,"content":{"application/json":{"schema":{"type":"object","required":["email","password"],"properties":{"email":{"type":"string"},"password":{"type":"string"},"nickname":{"type":"string"}}}}}},"responses":{"201":{}}}}}},"operationId":"createUser"}) });

Part of these workflows

OpenAPI required-params extractor is one step in this skill pack, each sold as a single call:

• API contract drift check - The 'did this API contract change in a way that breaks our integration?' workflow. Diff two OpenAPI snapshots structurally, lint the new one for agent-readiness regressions, extract the endpoint surface for inventory comparison, validate a known-good payload against the new contract, and summarize security-relevant changes. Six tools, one go/no-go answer on whether the upstream API broke us.

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