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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds useful non-obvious behavior: the payload is ~90 KB, Apache-2.0, dependency-free, and exposes Rhylthyme.renderTimeline(container, program). It does not mention caching or whether the source is versioned/pinned.

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?

A single dense sentence that front-loads the return value and packs license, size, dependency status and API surface with no 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?

With no output schema, the description adequately covers the return payload (source code, size, license) and how to consume it, which is everything an agent needs to call this no-argument tool 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?

The tool takes zero parameters, so the baseline is 4. The description does describe the arguments of the function it exposes (container, program), which is helpful context even though it is not tool input.

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 precise verb+resource (return the timeline renderer's JavaScript source) and adds distinguishing detail — license, size, dependency-free, and the exported API. It is clearly separable from siblings like preview_timeline or visualize_schedule, which render rather than ship source.

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?

Gives a concrete triggering condition: use it for an HTML page or artifact that cannot load external scripts. That is a clear when-to-use, though it does not explicitly name the alternative (e.g., fetching the script from a CDN or using preview_timeline) as a when-not.

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