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

The description discloses behavior well beyond the annotations: `note` replaces the whole note rather than appending, an empty string clears it, the change is applied immediately with no confirmation step, and the agent should report the new text back. This explains the destructiveHint=true replacement semantics in concrete terms the annotations cannot.

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 one dense paragraph, but it is front-loaded with the trigger and every sentence earns its place: scope, sibling exclusion, prerequisite, replacement semantics, and confirmation instruction. No filler despite the length, which is justified by the destructive replacement behavior.

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?

An output schema exists, so return values need not be explained. The description covers trigger, prerequisites, mutation semantics, and sibling routing, which is everything an agent needs to invoke this 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?

With 0% schema description coverage, the description carries the full burden and does so: it explains that `note` replaces the entire note (and how to append), that an empty value clears it, and that `exercise_slug` should come from `get_exercise_library`. Both parameters are given meaning absent from the schema.

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 states a specific verb and resource ('add, change or clear their own note on an exercise, built-in or custom') and explicitly distinguishes this from the sibling case where a custom exercise's how-to belongs in `notes` on `update_custom_exercise`. An agent can identify the tool's scope without opening any schema.

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 explicit when-to-use ('user asks to add, change or clear their own note'), the counter-case (custom exercise how-to goes elsewhere), the prerequisite workflow (fetch slug and current note via `get_exercise_library`), and the invocation condition ('when the user asks for the note or has just agreed to it'). Nothing is left to inference.

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