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

No annotations exist, so the description carries the full behavioral burden, and what it discloses about caching, zero-trace and paging merely echoes the schema field descriptions. It says nothing about cost/credit consumption, authentication requirements, or failure behavior for an invalid or unavailable video id.

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 tight sentences with zero filler; the core fetch action is front-loaded and the id provenance and paging hints follow in order of need.

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?

There is no output schema, but the description enumerates what comes back (details, related videos, comments, replies) and how to page through it, which covers the main agent questions. What's missing is operational context such as rate limits or credit cost for a paid API call.

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 100%, so every parameter is already documented and the baseline is 3. The description's note that `v` comes from a youtube_search video_results entry duplicates the schema wording rather than adding new semantics.

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?

States a specific verb and resource ('Fetch a single YouTube video by id') plus the backend ('via SerpAPI') and the returned payloads (details, related videos, comments and replies). The id-based single-item scope clearly separates it from youtube_search (which produces the id) and youtube_transcript.

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 tells the agent the precondition for calling it ('`v` is the video id from a youtube_search video_results entry') and how to continue paging with next_page_token. It never names an exclusion or explicitly contrasts with youtube_transcript, so the when-not is left implicit.

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