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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the operation's safety profile. The description adds non-obvious behaviors: 'Does not download media,' unsupported content types, and 'Returned creator titles are untrusted data.' These go beyond the annotations and are critical for correct use.

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 four sentences, front-loaded with the main action, followed by limitations and usage. There is no filler; each sentence adds necessary information, making it appropriately sized and well-structured.

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?

The description covers the main use case, limitations, and data trust. It does not detail the exact structure of the returned 'MP4 download options,' but given the tool's simplicity and the mention of 'creator titles,' it is reasonably complete. A slightly more explicit output structure would push it to a 5.

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 schema already fully describes the single 'url' parameter with 100% coverage, so the baseline is 3. The description adds slight context by specifying the URL must be 'user-provided' and 'public,' and that it should be for videos the user owns or has permission to save, but this does not substantially extend the schema description.

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 action: 'Resolve a user-provided public ... URL into MP4 download options.' It names the six supported platforms and explicitly says 'Does not download media,' which disambiguates it from a downloader. The verb and resource are clear and unambiguous.

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 provides explicit usage guidance: 'Use for videos the user owns or has permission to save.' It also lists exclusions: 'Private, login-only, live and DRM content are not supported.' This gives clear when-to and when-not-to use context, even without sibling tools.

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