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

Goes well beyond annotations. Annotations indicate mutation (readOnly=false) and non-idempotency, but the description adds critical details: it saves the asset but does not add it to the video until later, it returns a RIGHTS CHECK that must be relayed, and it verifies neither ownership nor license. Also clarifies the project_id scoping behavior.

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 dense but efficiently organized. It leads with the scope, then the purpose, supported link types, usage rule, as_kind behavior, next steps, and rights caveat. Every sentence adds value, though it could be slightly tighter by trimming redundancy (e.g., the phrase 'download media' appears twice).

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?

Covers the essential operational context: what it does, what it doesn't do (not added to video), what to do next, and the rights caveat. Lacks details on return structure beyond 'project identity' and 'RIGHTS CHECK', and no error handling or rate-limit info, but these are minor for a fetch tool. The output schema is absent, so description must carry this weight, which it does adequately.

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 only 33% (only project_id has a description), but the description compensates fully. It explains what URL formats are accepted (direct links vs page links), clarifies that as_kind is optional and only for forcing audio extraction, and reinforces project_id immutability. This adds meaning beyond the schema.

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 clearly states the verb (download media from a LINK), the resource (URL) and the action (save as project asset). It also specifies the project scope. However, it does not explicitly differentiate from the sibling tool download_url, which could overlap in purpose. The phrase 'for something they want in the edit' narrows it to project assets, but a direct comparison is missing.

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?

Provides explicit when-to-use guidance: 'Use this whenever the user pastes a URL for something they want in the edit; never tell them to upload a file you could have fetched.' It also explains when to use as_kind ('only to force audio-only from a video page') and what to do next (insert_media/add_music). This is clear and actionable.

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