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

Beyond the readOnly/idempotent annotations, it discloses cost and side effects ('Free, instant, creates nothing'), the failure mode ('a video outside the published trend set answers 404'), a guaranteed null field ('`series.selected` is always null and `series.reason` says why'), and a prompt-injection warning about untrusted caption/hashtag/brief text. These are all facts an agent cannot get from the annotations or schema, and none of them contradict the readOnly/idempotent hints.

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 critical constraint (new original video, not a copy; no series chosen here) is front-loaded and the WHEN/route ordering is logical. It is dense and heavily capitalized, with several ideas packed into one block, so it is slightly heavier than needed, but no sentence is filler.

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 carries the full burden of explaining return values, and it does: public row, niche with premise, brief, next_steps, and the always-null series fields. Combined with the 404 note and the injection guidance, an agent has everything it needs to call this correctly and interpret the result.

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 coverage is 100% and the schema already documents `trend_id` as 'A trend video's `id` from a `list_trends` row. Not a url.' The description reinforces this with the 404 consequence and the contrast against `analyze_video`'s url parameter, adding a little error-handling meaning beyond the schema, but the core semantics are already structured.

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 a specific verb+resource+constraint ('returns ONE trend video's public row, the NICHE it belongs to, a written `brief`... and `next_steps`') and explicitly enumerates the returned fields. It also carves out a clear boundary against siblings by stating what it does NOT do (choose a series) and naming `list_series` as the tool that does.

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 gives an explicit WHEN ('right after the user picks a video from `list_trends`, or hands you a trend id and asks how to make one like it') and an explicit alternative for a different input type ('`analyze_video` takes an arbitrary url'). It also lays out the downstream route (analyze_video → list_series → generate_story_video), so the agent knows where this tool sits in the workflow.

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