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

Annotations already declare this as a safe, idempotent read. The description adds meaningful behavioral context beyond annotations by stating the tool is free and requires no key, which helps the agent understand access constraints.

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?

Two short sentences, front-loaded with the core purpose and followed by the access constraint. Nothing is wasted and the format is easy to parse.

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 one-parameter getter with complete annotations and schema coverage, the description is nearly sufficient. It could say slightly more about what "in full" entails, but no output schema exists and the critical access detail is included.

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 single listing_id parameter is fully documented in the schema, including source examples. The description adds only "one listing" and does not elaborate on the identifier semantics, so baseline 3 is appropriate given high schema coverage.

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 that it returns one listing in full, which is specific enough to distinguish this single-item getter from list/search siblings like search_listings and my_listings. The verb is only implied by the tool name, but the resource and scope are clear.

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?

"One listing in full" implies usage for fetching a single listing by id, and "Free, no key" gives context about access. However, it does not explicitly say when to choose this over search_listings or my_listings, nor does it mention prerequisites beyond keylessness.

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