x402 Doctor

Quick x402 endpoint check (free)

x402_quick_check

Read-only

Free: does this x402 endpoint work for a paying agent? Returns pass, warn or fail with the number of problems and the top three. Limited to 10 calls per hour. For every check use x402_diagnose ($0.01); for code changes x402_fix ($0.05); before paying someone else's endpoint x402_preflight ($0.001).

Input Schema

Name	Required	Description
`url`	Yes	The x402 endpoint (public http(s) URL), e.g. https://api.example.com/paid
`body`	No	Example JSON request body, for a POST route that checks its input before the 402 (implies POST). Without it, {} is sent and the requestBody example in the endpoint's /openapi.json is tried.
`method`	No	HTTP method of the paid route (default: GET, then POST)

Output Schema

Name	Required	Description
`url`	No
`next`	No
`overall`	Yes	pass, warn or fail
`failures`	Yes
`warnings`	Yes
`top_problems`	Yes	Up to three problems, failures first

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 29, 2026
- removedInput schema / additionalProperties
```
Removed value: -false
```
- changedOutput schema / additionalProperties
```
Previous value: -trueNew value: +{}
```

Changed1 schema field changedOct 20, 2026

addedInput schema / properties / body

Added value: +{
+  "description": "Example JSON request body, for a POST route that checks its input before the 402 (implies POST). Without it, {} is sent and the requestBody example in the endpoint's /openapi.json is tried.",
+  "maxLength": 16384,
+  "type": "string"
+}

Changed1 schema field changedOct 9, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": true,
+  "properties": {
+    "failures": {
+      "type": "number"
+    },
+    "next": {
+      "type": "string"
+    },
+    "overall": {
+      "description": "pass, warn or fail",
+      "type": "string"
+    },
+    "top_problems": {
+      "description": "Up to three problems, failures first",
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "url": {
+      "type": "string"
+    },
+    "warnings": {
+      "type": "number"
+    }
+  },
+  "required": [
+    "overall",
+    "failures",
+    "warnings",
+    "top_problems"
+  ],
+  "type": "object"
+}

First observedSep 25, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Adds context annotations do not carry: it is free, rate-limited to 10 calls per hour, and returns a pass/warn/fail verdict with a problem count and the top three problems. Annotations already cover read-only and open-world behavior, so the remaining gap is only that it doesn't say how it verifies (e.g. whether it actually issues requests).

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the free quick-check purpose and the return shape, then the routing. The pricing parentheticals are dense but each earns its place by driving cost-aware selection; slightly compacted phrasing would improve readability.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema, full parameter coverage, and read-only annotations already provided, the description supplies the missing pieces: cost model, rate limit, verdict semantics, and sibling routing. Only the verification mechanics are left implicit, which is a minor gap for an endpoint liveness check.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and the url, body, and method descriptions already explain defaults and fallbacks in detail. The prose adds nothing about parameters, so this sits at the baseline for a fully documented schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('does this x402 endpoint work for a paying agent?') and immediately names the decision output (pass/warn/fail with problem count and top three). This is distinguishable at a glance from siblings like x402_fix or x402_preflight.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly positions itself as the free entry check and routes to three alternatives by condition and price: x402_diagnose for every check, x402_fix for code changes, x402_preflight before paying third-party endpoints. The 10-calls-per-hour cap further defines when it is appropriate.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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