Aether Layer: EU VAT number validation (VIES)

Agent Readiness Check

agent_readiness_check

Read-onlyIdempotent

Deterministically grade an MCP tool catalog or a third-party x402 endpoint. Provide exactly one of: mcp_url (public https MCP server; initialize + tools/list), x402_url (public https resource; the gateway requests it WITHOUT an X-PAYMENT header and reads the 402), or tools (a JSON tool manifest). Never pays or signs a payment. No LLM is used. Requires an API key in Authorization: Bearer or X-Api-Key.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "agent_readiness_check"
  }
}

Input Schema

Name	Required	Description
`tools`	No	Tool manifest, as returned by tools/list.
`mcp_url`	No	Public https URL of a remote MCP server (Streamable HTTP).
`x402_url`	No	Public https URL of a third-party x402 resource. The gateway never sends X-PAYMENT.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 12, 2026

TDQS

A4.6/5.0

Behavior4/5

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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, so the bar is lower, yet the description still adds real behavioral context: it never pays or signs a payment, uses no LLM (deterministic), and requires an API key via Authorization: Bearer or X-Api-Key. It stops short of describing output shape or any cost/rate limits.

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

Conciseness5/5

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

Front-loads purpose, then the mode-selection rule, then the safety and auth constraints. Every sentence carries distinct information with no padding.

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?

For a grading tool with no output schema, the definition covers inputs, auth, and determinism, but says nothing about what a "grade" returns — score scale, verdict fields, or report format — which an agent needs to interpret the result.

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%, so the baseline is 3; the description earns an extra point by adding usage detail the schema lacks — the mutual exclusivity of the three parameters and the fact that mcp_url drives initialize + tools/list while x402_url is read without an X-PAYMENT header.

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: "Deterministically grade an MCP tool catalog or a third-party x402 endpoint." It immediately distinguishes three input modes and would be unmistakable against the unrelated sibling validate_vat.

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?

Gives an explicit selection rule — "Provide exactly one of" mcp_url, x402_url, or tools — and qualifies each mode (public https MCP server with initialize + tools/list; public https resource read without X-PAYMENT). The agent knows which argument to supply and under what conditions.

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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