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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds non-obvious behavior beyond them: the wait screen when the lesson is still being built and the automatic start when ready, plus the 'no microphone' constraint distinguishing it from interactive audio tools.

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?

Two tight sentences, front-loaded with the action, then the timing/behavioral nuance. No filler or redundancy.

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?

For a single-parameter opener with annotations covering safety and no output schema, the description supplies everything an agent needs: what happens visually, the interaction constraint, and the sequencing with lesson_create. Nothing material is missing.

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?

There is one required parameter, lesson_id, and schema description coverage is 0%, so nothing documents its format or expected value. The name and schema title 'Lesson Id' are largely self-explanatory, but the description contributes no additional meaning such as where an id comes from (e.g. lesson_create or lessons).

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 concrete verb+resource ('Open a lesson in a player window in the chat') and scopes the modality (audio, slides, subtitles; no microphone), which separates it from dialogue_* tools and open_in_browser. It does not explicitly name a confusing sibling like lesson_get or lesson_audio, so differentiation is implicit rather than spelled out.

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 real when-to-use context: 'Can be called right after lesson_create' and explains the wait-screen behavior while the lesson builds. No when-not-to-use or explicit alternative routing, so it stops short of a full 5.

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