A2UI Atomic Catalog

required_catalogs

Read-onlyIdempotent

Given an A2UI payload, return the resolvable catalog URIs it needs (deterministic — pure function of the atoms).

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": {
      "payload": "<payload>"
    },
    "name": "required_catalogs"
  }
}

Input Schema

Name	Required	Description	Default
`payload`	Yes	The A2UI payload to inspect: {title, theme, blocks:[...]} in the blocks dialect.

Output Schema

Name	Required	Description	Default
`required_catalogs`	Yes	Catalog URIs the payload needs (base catalog first).

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 10, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already declare this as read-only, idempotent, non-destructive, and closed-world. The description adds meaningful behavioral context by calling it deterministic and a pure function of the atoms, which reinforces that repeated calls produce stable results without side effects. It does not describe handling of unresolved catalogs or edge cases, but the core behavior is well disclosed.

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?

The definition is a single compact sentence with the core input and result front-loaded. The parenthetical determinism note adds useful precision without unnecessary wording.

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?

The tool is simple, read-only, fully described by its schema, and has an output schema, so the description covers enough for correct invocation. The only minor gap is that 'resolvable' is not further explained, though the output schema likely supplies the returned URI details.

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 description coverage is 100%, so the nested payload and blocks semantics are already documented in the schema. The description restates that the input is an A2UI payload and mentions atoms, but adds no further parameter-level guidance beyond what the schema provides.

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

Purpose4/5

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

States a specific action and result: inspect an A2UI payload and return the catalog URIs it needs. The deterministic pure-function framing makes the purpose clear, though it does not explicitly contrast itself with list_catalogs or get_catalog.

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 input condition is implied by 'Given an A2UI payload,' which tells the agent when the tool is applicable. However, it does not explicitly say when to choose it over list_catalogs, get_catalog, or other catalog-related siblings.

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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