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

Annotations only tell the agent it is non-read-only and non-destructive; the description adds the valuable operational context that annotations cannot: personal link, minimum 5-minute lifetime, a 20-downloads-per-product-per-day quota, and auth. Minor gap: it references 'expires_at' which is not defined anywhere (no output schema), and it does not say what happens when the quota is exhausted.

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 sentences, front-loaded with the action and resource, with no filler. Slightly dense with parenthetical asides ('longer for large files, see expires_at'), but every clause carries information.

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 two-param, no-output-schema tool, it covers auth, quota, and link lifetime well enough to call it correctly. The remaining hole is file_index semantics and what the response actually contains (the URL field), which the agent must guess.

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 0%, so the description must carry parameter meaning. It explains where product_id comes from (list_purchases) but says nothing about file_index – how to determine it, what 0 means, or that it selects among multiple files. Half of the parameter surface is undocumented.

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, resource and scope: 'Creates a signed download link for one file of a product the signed-in customer owns'. It even names the sibling (list_purchases) that supplies the product_id, so an agent can tell it apart from get_product or list_purchases without opening a schema.

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?

Gives a clear precondition ('from list_purchases') and an auth requirement ('Requires signing in'), which routes the agent to the right prerequisite tool. It does not state exclusions or alternatives (e.g., when to use get_product instead), so it stops short of a 5.

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