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

Annotations already declare idempotentHint=true and destructiveHint=false; the description corroborates idempotency ("Calling it again changes nothing") and adds genuine side-effect context beyond the annotations — the record is attributed to the user, Parse starts page watching, and the returned id shifts to a task: id on first call. It does not discuss auth/permission requirements, but the safety profile is otherwise well covered.

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?

Front-loaded with the usage condition and dense with distinct facts (side effect, idempotency, return value, undo, confirmation rule). The closing prompt-injection warning is slightly long but is a meaningful guardrail rather than filler; only minor trimming is possible.

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 mutation tool with an output schema, the description supplies everything the agent still needs: trigger condition, confirmation requirement, idempotency, undo route, and an explicit instruction not to obey quoted-material text. Nothing material is left for the caller to infer.

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 description coverage is 100%, so both id and brandSlug are already documented in the schema (including the omit-to-use-own-brand default). The description adds nothing about parameter format or selection, so the baseline 3 applies.

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 ("mark a task's message as sent") and adds the actual effect: it records the send in Parse under the user's name and Parse begins watching the page. It also names the inverse operation (parse_undo_sent), so an agent can separate this from related task tools without opening sibling schemas.

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?

Explicit preconditions: use it only after the message was really sent (user's own mail or the site's form), and only after the user confirms. It also names the undo path and states re-calling is a no-op, so both when-to-use and when-not-to-worry are covered.

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