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

Annotations already declare readOnly, non-destructive, and closed-world, so the safety bar is low. The description still adds real behavioral value: results come back as images rather than files, the call consumes no credits, and — critically — a video clip returns only its poster frame, not the actual content at that second.

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 first two sentences are front-loaded and information-dense. The closing sentence ('Read every word you changed before you tell your user it is done') is confusingly worded, reads as an instruction to the agent rather than a description of the tool, and does not clearly earn its place.

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 only two well-documented parameters and no output schema, the description covers the key gaps: what is returned (images), what each second maps to, and that nothing is exported. Only the response shape (image count, format, dimensions) is left unstated, which is a minor omission.

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%, so pid and seconds are already documented, including the 8-item limit. The description's only added meaning is that seconds are timeline positions whose composed frame you get back, which is marginal beyond the schema's 'Timeline positions, in seconds. Up to 8.'

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 — viewing a project's current timeline as composed frames returned as images — and implicitly separates itself from export_video/render_video by noting 'no export and no credits'. The clause explaining that a motion graphic shows its real frame while a video clip shows its poster makes the scope unambiguous.

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?

The usage context is only implied: check the timeline at given seconds, and it costs no credits, which nudges toward using it before an export. It never names alternatives such as get_timeline, render_video, or export_video, and the closing sentence about reading changes before reporting done is a workflow reminder rather than a when-to-use rule.

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