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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the description adds value by disclosing that no API key is needed, the cost (0.01 USDC/query), a session limit (max 20 queries), and that it is free. This goes beyond the structured annotations with operational details.

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

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

The description is a promotional paragraph with redundant claims ('No API key needed' and 'FREE preview — no key, no payment' repeat the same point), excessive emojis, and imperative calls to action. It is not front-loaded with a clear statement of function; instead it leads with marketing. Key information is buried amid filler.

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

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

For a simple tool with two optional parameters and no output schema, the description provides cost, authentication, and usage examples. However, it omits what the response contains (schema says 'public metadata only') and does not mention the default behavior of slug when routed via /mcp/data/{slug}/http. These gaps are partially covered by the schema, but the description could have added more operational context.

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

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

The schema description covers 100% of the parameters (slug and question) with clear explanations and defaults. The tool description adds no parameter-specific meaning; it only gives example questions for the 'question' field. Since schema coverage is complete, a baseline of 3 is appropriate.

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

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

The description states it is a 'FREE preview' of a specific listing (usnwatch: Ubuntu Security Notices), implying the tool provides a taste of the data. However, it never explicitly states the verb (e.g., 'preview a listing') and relies on the schema description for clarity. It distinguishes from paid query tools via 'no key, no payment' but lacks a direct action statement.

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

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

The description tells the agent to 'call this now' and provides sample questions, indicating immediate use without credentials. It does not mention alternatives or when not to use this tool versus data_session_query or other siblings. The free/no-key aspect implies usage for evaluation, but no explicit exclusions or comparisons are given.

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