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

Annotations only say this is a non-idempotent, non-destructive write; the description adds real context beyond that: mention emails are resolved server-side to UUIDs and `@<email>` literals inside `text` are rewritten into mention spans, plus the required `tasks:write` API-key scope. What it omits is what the response contains and whether duplicate comments are rejected.

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?

Three tight sentences, front-loaded with the action, then the two behaviors an agent cannot infer (mention resolution, threading), then the auth scope. Nothing redundant with the schema.

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 6-parameter write tool with 83% schema coverage, no output schema, and annotations covering the safety profile, the description supplies what is missing: the mention-substitution mechanic, threading, and the required scope. An agent could call this correctly without further reading.

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 already 83%, so the baseline is 3; the description goes further by explaining the side effect of `mentions` on the `text` body (literal substitution of `@<email>`), which the schema does not convey. `ref`, `account`, and `workspace` are left to their schema descriptions.

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?

Opens with a specific verb+resource ("Add a comment to a task"), so the operation is unambiguous. It does not explicitly distinguish itself from nearby siblings like pm_update_task_comment or pm_add_comment_reaction, but the create/append semantics are clear from the verb.

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 conditional usage hints ("Pass `replyTo` to thread", mentions array for @-mentions) but never states when to prefer this over pm_update_task_comment or pm_add_comment_reaction, nor any prerequisite like task access. Usage is implied by the parameter hints rather than declared.

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