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

Annotations already disclose the safety profile (readOnly false, non-idempotent, non-destructive), lowering the bar. The description adds one genuinely useful behavioral detail for a non-idempotent write — slides_hidden_s is a running total, not an increment. However, it never says whether a call overwrites prior progress or merges it, and the dangling 'Completed from 95 %' is unexplained.

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?

It is short, but it is a single run-on construction of colon-and-comma fragments with no front-loaded statement of purpose. The trailing 'Completed from 95 %' fragment dangles without context and does not earn its place as written.

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 four-parameter write tool with no output schema and no schema descriptions, the parameter coverage is decent, but the description omits any statement of what the call changes, whether it is safe to repeat, and what (if anything) is returned. It is adequate but leaves real gaps for a mutation tool.

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?

With 0% schema description coverage, the description carries the full burden and mostly does: it gives units for position_s (seconds), enumerates mode as listen/watch/read, and clarifies slides_hidden_s as a total. Only lesson_id is undocumented, and that is self-evident from its name.

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 conveys what data the tool captures ('Where the user stopped') but never states the action verb (save/report/record), so the purpose is only implied. It also fails to distinguish itself from close siblings like lesson_get, lesson_open, and progress. Reads more like field documentation than a statement of what the tool 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?

There is no when-to-use guidance at all: nothing says whether this should be called during playback, on pause, on exit, or how it relates to lesson_open/lesson_get/progress. The agent must infer the trigger condition from the name alone.

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