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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds genuinely non-obvious behavior: it returns metadata only and 'never the file's bytes', preventing an agent from expecting a download. It doesn't cover error behavior for a missing/invalid id, which keeps it from a 5.

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 short sentences, each earning its place: what is returned, when to use it, and the critical 'metadata only' caveat. The most important constraint is front-loaded in the returned-field list and reinforced at the end.

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 an output schema present, return value documentation is not strictly required, yet the description still enumerates the key fields. The one real gap is the id-versus-name ambiguity, which matters for a tool whose only parameter is required.

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 all parameter meaning—and it introduces a mismatch: the sole required parameter is named 'name' in the schema, while the description says the file is looked up 'by id'. An agent cannot tell whether to pass a file name or a file id, or what format either takes.

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 ('Return the metadata') and resource ('one uploaded file by id'), names the exact fields returned (cdn_url, name, size, content type), and explicitly distinguishes itself from list_files. An agent can tell what this does without opening the 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?

It gives a concrete use case—'Recovers the cdn_url for a file listed by list_files'—which tells the agent when to reach for this tool and which sibling precedes it. It stops short of stating exclusions (e.g., that it should not be used to fetch file bytes versus download_media), so it's clear context rather than full when/when-not guidance.

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