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

Annotations already supply readOnlyHint and idempotentHint. The description adds meaningful behavioral context beyond those annotations by disclosing that the tool returns links only, that links are signed, and that they expire, with an instruction to fetch promptly.

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 two tight sentences with no filler. The core purpose is front-loaded, and the critical caveat about signed, expiring links is delivered immediately after.

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 read-only tool with two well-documented parameters, the description is complete: it names the resource, enumerates returned media types, and warns about link expiration. There is no output schema, but the description covers the main return value shape sufficiently.

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%, so the schema fully documents both 'id' and 'expand'. The description does not add parameter-specific semantics beyond the schema, but that is acceptable because the schema already carries the load.

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 a specific verb and resource: returning 'direct media URLs for one post.' It enumerates exactly what is included (no-watermark video, watermarked video, audio, covers, images) and distinguishes this from sibling tools like stats, comments, or transcript by emphasizing that it provides links only, not bytes.

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 implies usage: call it when you need media URLs for a single post. It also gives a practical constraint ('fetch promptly' because links expire), but it does not explicitly name alternatives or state when not to use this tool versus sibling tools.

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