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

With no annotations, the description carries the full burden. It discloses that the tool does not download, is free (doesn't count against quota), returns a specific set of fields, and notes some fields may be unavailable ('when available'). This is commendable, though it doesn't mention potential error cases or rate limits.

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 longer than average but well-structured: it opens with the core function, then lists platforms, return fields, use cases, exclusions, and a practical tip. Each section earns its place; the only minor deduction is length, which is justified by the tool's breadth.

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?

Despite having no output schema, the description explicitly enumerates all returned fields (title, uploader, duration, etc.) and the full list of supported platforms. It also covers when to use, when not to use, and quota behavior, making the description self-sufficient for a single-parameter metadata tool.

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 input schema has 100% coverage for the url parameter, including supported platform examples. The description repeats some platform information but adds no additional parameter-level semantics beyond the schema. Baseline 3 is appropriate.

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 tool fetches metadata without downloading, which is a specific verb+resource. It explicitly distinguishes from the sibling download_video and lists all supported platforms, making the tool's scope 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?

Provides explicit use cases ('what is this video about', 'how long is this track') and exclusions ('Do NOT use this tool when... use download_video'). It also advises calling this tool before download_video to confirm existence or check licensing, which is strong contextual guidance.

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