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

Goes well beyond the annotations by disclosing the side effect on flow-step tasks ("also completes its step, as the check box does") and the exact idempotent-replay contract: a repeat returns the task, reports what the original call applied, and makes no change if the task was modified in between. That conflict/no-op semantics is exactly the kind of behavioral detail an agent cannot infer from idempotentHint=true alone.

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 dense sentences, front-loaded with the core action and free of filler. The final clause ("changes nothing if the task changed since") is compressed enough to require a reread, which slightly undercuts clarity.

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 no output schema, it covers the essentials: attribution of the completion, the flow-step side effect, and idempotent retry/conflict behavior. The main remaining gap is the `note` parameter and any permission or error conditions.

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%, so the description should compensate, but it only restates the idempotency_key retry rule that the schema already documents. The optional `note` parameter is unexplained in both the schema and the description, and `task_id` is only implicitly referenced as "the same id".

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 ("Marks a task done") plus an attribution scope ("recorded as completed by this seat") and a side effect for flow-step tasks. It is clearly distinguishable from siblings like reopen_task, skip_task, or complete_tasks_bulk, but never names them explicitly to reinforce the distinction.

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?

The only usage guidance is about retry behavior ("Pass the same idempotency_key when retrying"). There is no guidance on when to prefer this over complete_tasks_bulk, skip_task, or reopen_task, and no stated preconditions such as required permissions or whether an already-completed task is acceptable input.

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