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

Annotations already declare a non-read-only but non-destructive, non-open-world mutation. The description adds one genuinely useful behavioral fact: Google sets the completion timestamp server-side, so no time value is passed. It says nothing about idempotency, whether re-completing is an error, or permission requirements.

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 short, front-loaded sentences with zero filler; the action comes first and the behavioral note second.

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 simple three-parameter mutation with no output schema, the description covers the core action and the server-side timestamp, but leaves the identity of listId/taskId and the result of the call unspecified. Adequate but with clear gaps.

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 only 33% — only 'mailbox' is documented (pointing at list_authorized_mailboxes). The description does not explain listId or taskId at all, so it fails to compensate for the undocumented parameters as the low-coverage rule requires.

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 specific verb and resource ('Mark a task done') that an agent can map directly to the Google task object. It is reasonably distinguishable from create/delete/update_google_task, though it never explicitly names those siblings as alternatives or boundaries.

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?

No when-to-use guidance, no prerequisites, and no routing to alternatives such as update_google_task (for un-completing) or delete_google_task. The agent must infer the usage context entirely from the name.

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