Become discoverable

Build once, register reliably, and keep your resources discoverable by agents.

Why This Matters

If agents can't discover your API, they can't call it. Bulletproof discovery turns your endpoint from merely listed to reliably invocable.

When metadata and runtime 402 behavior agree, agents succeed on the first pass. You get fewer failures, less debugging churn, and more real agent traffic.

Publish OpenAPI as the canonical machine-readable contract.
Treat runtime 402 challenge behavior as the final source of truth.

Copy for Agents

Paste this directly into your coding agent. It should handle discovery implementation and validation end-to-end.

Implement discovery for this server and make it pass.

Discovery strategy:
- OpenAPI is the canonical discovery contract. Publish your spec at /openapi.json.

Schema guidance (important):
- Each invocable route should expose an input schema.
- In OpenAPI, define requestBody.content["application/json"].schema.
- This is required for reliable agent invocation and robust listing behavior.
- Add high-level guidance in info.x-guidance for user-friendly discovery. This document should explain to an agent how to use your API at a high level.

OpenAPI payable operation must include ALL:
- x-payment-info with:
  - price (structured object):
    - fixed: { mode: "fixed", currency: "USD", amount: "<amount>" }
    - dynamic: { mode: "dynamic", currency: "USD", min: "<min>", max: "<max>" }
  - protocols (array of objects):
    - { "mpp": { "method": "", "intent": "", "currency": "" } }
- responses: { "402": { description: "Payment Required" } }

SIWX (identity-only) routes:
- Declare a security scheme named "siwx" in components.securitySchemes.
- Reference it on each identity-gated operation: security: [{ "siwx": [] }].
- Do NOT add x-payment-info to SIWX-only routes — that classifies them as paid.

Rules:
- Runtime 402 behavior is authoritative over static metadata.
- "amount" is for both runtime accepts and x-payment-info fixed pricing.

Workflow:
1) Audit discovery and probe failures.
2) Fix discovery metadata and 402 behavior.
3) Re-run audits until clean.
4) Register on MPPScan at https://mppscan.com/register.

Validation commands:
npx -y @agentcash/discovery@latest discover "$TARGET_URL"
npx -y @agentcash/discovery@latest check "$ENDPOINT_URL"

These yield warnings regarding the discovery document and how it can be improved.

Done when:
- resources are discovered from OpenAPI
- no critical parser/probe errors remain
- server is registered on MPPScan with no failed resources

Test your API

Run discovery against your origin to see what MPPScan resolves before you register.

Origin or endpoint URL

Runs discoverOriginSchema against the origin and probes each discovered route. Nothing is registered.

Discovery Strategy

OpenAPI is the canonical discovery format. Use it for the cleanest machine-readable contract and best agent compatibility.

The x-payment-info fields are a superset of the IETF API payment spec. The fields do not collide, so your service is still compatible if you already follow the IETF standard.

Expected location: GET /openapi.json

Requirements

Top-level fields: openapi, info.title, info.x-guidance, info.version, paths.
For paid operations: responses.402 and x-payment-info.
Set x-payment-info.protocols (array of protocol objects) and one pricing mode (fixed or dynamic) with currency.
Use OpenAPI security + components.securitySchemes for auth declaration.
Add high-level guidance in info.x-guidance for agent-friendly discovery.

Pricing modes in `x-payment-info`

Fixed: { price: { mode: "fixed", currency: "USD", amount: "<amount>" } }
Dynamic: { price: { mode: "dynamic", currency: "USD", min: "<min>", max: "<max>" } }

Minimal valid example

{
  "openapi": "3.1.0",
  "info": {
    "title": "My API",
    "version": "1.0.0",
    "description": "example demo server",
    "x-guidance": "Use POST /api/search for neural web search. Accepts a JSON body with a 'query' field."
  },
  "x-discovery": {
    "ownershipProofs": ["<proof-1>"]
  },
  "paths": {
    "/api/search": {
      "post": {
        "operationId": "search",
        "summary": "Search - Neural search across the web",
        "tags": ["Search"],
        "x-payment-info": {
          "price": {
            "mode": "fixed",
            "currency": "USD",
            "amount": "0.010000"
          },
          "protocols": [
            {
              "x402": {}
            },
            {
              "mpp": {
                "method": "",
                "intent": "",
                "currency": ""
              }
            }
          ]
        },
        "requestBody": {
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "type": "object",
                "properties": {
                  "query": { "type": "string", "minLength": 1, "description": "The query string for the search" }
                },
                "required": ["query"]
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "Successful response",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "results": { "type": "array", "items": { "type": "object" } }
                  },
                  "required": ["results"]
                }
              }
            }
          },
          "402": { "description": "Payment Required" }
        }
      }
    }
  }
}

Discovery Precedence

MPPScan uses the OpenAPI document at /openapi.json to discover your API. It will also check the runtime 402 challenge behavior to ensure it is correct.

Order	Source	Expected Location
1	OpenAPI document	`/openapi.json`
2	`402` API Response	Correct `402` header response

SIWX (Sign-In with X) Routes

SIWX routes are identity-gated, requiring a wallet proof but no payment. Agents with a wallet can call these for free.

Declare a security scheme named siwx in components.securitySchemes.
Reference it on each identity-gated operation via security: [{ "siwx": [] }].
Do not add x-payment-info to SIWX-only routes, as that classifies them as paid.

{
  "components": {
    "securitySchemes": {
      "siwx": {
        "type": "apiKey",
        "in": "header",
        "name": "SIGN-IN-WITH-X"
      }
    }
  },
  "paths": {
    "/api/me": {
      "get": {
        "summary": "Get current user profile",
        "security": [{ "siwx": [] }],
        "responses": { "200": { "description": "OK" } }
      }
    }
  }
}

The scheme must be named siwx. Discovery resolves it by name. Routes with both x-payment-info and siwx security are classified as paid, not SIWX.

Endpoint-Only Fallback

If no OpenAPI document exists, a single endpoint URL can still be registered. MPPScan probes the URL directly via checkEndpointSchema from @agentcash/discovery.

The probe is method-aware. It tries POST first, then GET, PUT, PATCH, DELETE, and picks the first response with a valid MPP payment option.
The endpoint must return a parseable 402 challenge with at least one MPP entry.
Endpoints without an input schema are non-invocable and are skipped during registration. Publish an OpenAPI schema (or a 402 body that carries one) to make the endpoint registerable.
SIWX endpoints are registered as identity-only. No payment is required, but agents still need a wallet proof to call them.

curl -i -X POST https://yourdomain.com/api/route
curl -i -X GET https://yourdomain.com/api/route

Common Failure Reasons

These are the most frequent errors seen during registration.

Error	Likely Cause	Fix
Not Found	OpenAPI not found at `{origin}/openapi.json`	Add an OpenAPI document at `{origin}/openapi.json`
Input/Output Schema Missing	Operation has no input or output schema	Add an input and output schema to the operation
No Payment Modes Detected	No payment modes detected in the response	Add a valid payment mode to the response (MPP)

ErrorLikely CauseFix

Not Found

OpenAPI not found at {origin}/openapi.json

Add an OpenAPI document at {origin}/openapi.json

Input/Output Schema Missing

Operation has no input or output schema

Add an input and output schema to the operation

No Payment Modes Detected

No payment modes detected in the response

Add a valid payment mode to the response (MPP)

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For further questions, contact us at merchants@merit.systems.