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

Annotations already declare destructiveHint=true, idempotentHint=false, and openWorldHint=true, so the safety profile is covered. The description adds the underlying PUT endpoint and clarifies the 'now vs. given time' behavior, but it never explains what 'destructive' means here (state transition, irreversibility, repeat-call error behavior), which idempotentHint=false would make valuable.

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 fragments, front-loaded with the action and the key behavioral nuance (immediate vs. specified time). No wasted words; could arguably use one more clause on side effects rather than trimming further.

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 two-parameter mutation, the schema and annotations together cover most needs, but with no output schema the description should say what a successful completion returns or what happens on an already-completed task (relevant given idempotentHint=false). It leaves that gap unaddressed.

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 100%: both task_id (UUID pattern) and completed_at (ISO 8601 with timezone and default) are fully documented in the schema. The description's parenthetical restates the default-now behavior already present in the schema, so it adds no new semantics.

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+resource ("Mark a task completed") and narrows scope with the optional completion time, which clearly separates it from siblings like aryeo_create_task, aryeo_get_task, and aryeo_list_tasks. It doesn't explicitly name those siblings, but the action is unambiguous.

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 description implies usage by naming the operation but gives no when-to-use guidance, no preconditions (e.g. task must not already be completed), and no mention of alternatives or how this relates to similar state-changing siblings. An agent must infer everything about selection.

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