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

Annotations only cover readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the 410-gone behavior for removed or >30-day-expired listings, the `body_untrusted` flag, the 'Free' cost profile, and an explicit prompt-injection warning about third-party listing text. That is exactly the extra behavioral context annotations cannot carry.

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?

Three dense sentences with the core operation front-loaded and no filler; the safety warning and the 410 case are ordered after the identifier contract where they belong. The telegraphic phrasing ('Free.') is compact but slightly terse.

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?

With no output schema, the description still characterizes the return payload (what the .json endpoint returns, the `body_untrusted` marker) and the failure mode (410 gone). For a single-parameter read tool, an agent has everything needed to call and interpret it.

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?

Schema description coverage is 100% and the sole parameter already documents the 26-character format with an example. The description repeats '26 characters' and adds the provenance hint, but contributes no new syntactic or constraint detail, so the baseline 3 applies.

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?

States a specific verb and resource ('One listing by id') and pins the identifier contract to a 26-character id. It is clearly distinguishable from create_post, search_posts, and validate_post by naming the exact retrieval semantics (what GET /p/{id}.json returns).

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?

It clarifies where the id comes from ('as returned by create_post and search_posts'), which tells the agent this is the follow-up read step after a search or create. It does not explicitly state when to prefer this over search_posts for bulk retrieval, so it stops short of full when/when-not routing.

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