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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so safety is covered structurally. The description adds genuine value by enumerating what the response contains and confirming no download side effect occurs. It omits failure behavior for unsupported links or rate limits, keeping it at a 4.

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?

A single sentence that front-loads the resource and the returned fields, with the most important disambiguation ('without downloading it') placed at the end where it lands cleanly. No filler.

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 one-parameter, read-only, idempotent lookup with rich annotations and no output schema, the description is essentially sufficient and even previews the return fields. It leaves unstated what happens on an invalid or unsupported link, a minor but real gap.

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 coverage is 100%, and the schema itself already says 'Link to ONE video, reel, short or post (not a playlist or channel)'. The description adds nothing about the url parameter, so the baseline 3 applies — the schema does all the parameter work.

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?

Specific verb (look up) plus the exact fields returned (title, duration, uploader, available qualities), and it explicitly separates itself from download_video by stating 'without downloading it'. An agent can distinguish this from its three siblings without opening any 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?

The clause 'without downloading it' implicitly defines the use case as inspection-before-download and rules out the download path, effectively routing toward download_video for the other case. No explicit 'use X instead' sentence or prerequisite mention, so it falls 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.