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

With readOnlyHint=true and openWorldHint=true already present, the description adds useful behavioral context: output is always a title+thumbnail unit kept complementary, and generation is grounded in the user's own converting packaging. It does not contradict the annotations and goes beyond them by describing the tool's functional 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 front-loaded with the core action and unit constraint, then moves through trigger conditions, parameter combinations, and sibling routing. It is dense and written as long run-on sentences, but for a five-param multi-mode tool the length is justified and each sentence contributes.

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?

All major call modes are covered: new idea, existing video, follow-up, scoring, plus routing to sibling tools. The only notable omissions are the meaning of the 'topic' parameter and the exact return/output format, which matter more because there is no output schema; still this is detailed enough to select and invoke the tool safely.

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 already documents 4 of 5 params (80% coverage), so baseline is 3. The description adds combination semantics, e.g. passing both video and idea for follow-ups and using title/thumbnail_text for scoring, but it never explains the 'topic' parameter, leaving that mode ambiguous.

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 opening sentence names a specific verb+resource ('PACKAGE a YouTube video') and enumerates its two functional modes: generating title options/thumbnail text ideas or scoring existing ones. It also explicitly differentiates from siblings by naming evaluate_idea, suggest_ideas, and find_best_thumbnails as alternative tools.

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 exact triggers ('Call this whenever the user wants help with a title or a thumbnail...') and gives explicit exclusions: use evaluate_idea for idea-worthiness, suggest_ideas for brainstorming, and find_best_thumbnails for channel patterns. It also specifies when to pass video, idea, or both.

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