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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so 'Read-only.' is largely redundant. What the description does add is the shape of the returned records (video URL, poster image, originating line, page link, remix link), which goes beyond what any structured field provides and helps the agent decide whether the call answers the user's question.

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 sentence listing the returned fields is front-loaded and informative, and the usage clause follows immediately. The trailing 'Read-only.' is the one wasted fragment since the annotation block already carries that fact.

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, so the description correctly compensates by describing what each example contains. With zero required parameters and the single optional limit documented in the schema, an agent has everything needed to call this correctly.

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?

With a single parameter at 100% schema description coverage, the schema already documents 'limit' including its default of 6 and its 1-20 bounds. The description adds nothing about the parameter, so the baseline of 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 names the resource precisely (Example videos of Cast characters) and even enumerates the payload (video URL, poster image, source line, page link, remix link), which clearly separates it from siblings like list_characters and create_video_link. It stops short of an explicit verb phrase ('retrieve/fetch'), but the noun-first phrasing plus the function name leaves no ambiguity.

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 states two concrete when-to-use scenarios: showing the user what Cast makes before they open a link, and finding a proven prompt to adapt. There are no explicit exclusions or named alternatives (e.g., when to prefer list_characters for browsing characters), so it falls short of a full when/when-not statement.

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