Agent Paywire library

Check a payment endpoint

check_payment_endpoint

Read-onlyIdempotent

Check a public http(s) URL for an L402, x402, or MPP challenge and for agent discovery files. Two free reports per client per 24 hours, using the same client identification as GET /v1/changes. After that, the tool returns payment info for GET https://api.agentpaywire.com/v1/check and does not run the probe. Private, localhost, and metadata URLs are rejected. url is required. report.protocol is the passing challenge ids in the order l402, x402, mpp, joined with +, or null when none pass.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "url": "<url>"
    },
    "name": "check_payment_endpoint"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	Required public http or https URL of the payment endpoint.

Output Schema

Name	Required	Description	Default
`report`	No
`payment_required`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 24, 2026

addedOutput schema / properties / report / properties / protocol

Added value: +{
+  "type": [
+    "string",
+    "null"
+  ]
+}

changedOutput schema / properties / report / required

Previous value: -[
-  "ok",
-  "checks"
-]New value: +[
+  "ok",
+  "protocol",
+  "checks"
+]

AddedOct 24, 2026

TDQS

A4.4/5.0

Behavior5/5

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

Annotations already declare readOnly, idempotent, non-destructive, and open-world behavior, but the description adds substantial context beyond them: a hard rate limit of two free reports per client per 24 hours, the client-identification rule, the fallback behavior where it returns payment info and skips probing, and the URL safety restrictions. It also explains the report.protocol format.

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?

The description is front-loaded with the core check behavior and then packs in rate limits, fallback behavior, URL restrictions, and return-format notes. Most sentences earn their place, but 'url is required' is redundant given the required array and schema description, and the client-identification reference is slightly cryptic.

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

Completeness5/5

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

For a complex read-only probe with a free-tier cap and a payment fallback, the description covers the key operational details: what is probed, rate limits and identity, behavior after the cap, rejected URL classes, and how to interpret report.protocol. An output schema exists, so return-value documentation does not need to be exhaustive.

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

Parameters4/5

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

Schema coverage is 100% and the schema already describes url as a required public http or https URL. The description adds meaningful constraints by specifying that private, localhost, and metadata URLs are rejected, which goes beyond the schema's wording, though the 'url is required' sentence largely repeats structured data.

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?

The description states a specific verb ('Check') and a precise resource ('a public http(s) URL for an L402, x402, or MPP challenge and for agent discovery files'). No sibling tool covers this same resource, so the agent can distinguish it immediately from tools like get_protocol_facts or get_verification_status.

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

Usage Guidelines3/5

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

The description makes the intended usage clear (checking a public payment endpoint URL) and notes that private, localhost, and metadata URLs are rejected. However, it never says when to prefer this tool over alternatives or names any sibling as the option for a related task, leaving the routing decision implicit.

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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