YouTube Channel API

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

The description adds cost behavior (1 credit live read, 0 on cache hit), a return-shape guarantee (one object), and a naming-convention caveat, going beyond the readOnlyHint/openWorldHint annotations. The read-only annotation is consistent, and there is no contradiction.

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?

Six short sentences, each adding information, with the core purpose front-loaded. Some slight redundancy exists between 'Public data only' and 'Read-only', but no sentence is wasted.

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?

With no output schema, the description gives enough of the return contract by naming subscriber/video counts, one object, and platform-specific field names. It could list exact fields, but for a simple read-only query the current level is solid.

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?

Both parameters are fully described in the schema, so the baseline is 3. The description does not add parameter-specific meaning beyond naming 'cache hit' and a public URL, which the schema already covers.

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 opens with 'Subscriber and video counts for a public YouTube channel,' naming a specific output and resource. It also states the return shape ('Returns one object') and is distinguishable from sibling tools such as youtube_videos or 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?

Usage is implied: use when you need a channel's subscriber and video counts. It does not explicitly compare itself with siblings or state when not to use alternate tools, though the 'public data only' sentence hints at some exclusions.

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