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

Adds substantial behavior beyond the annotations: it discloses that the write 'overwrites that item's existing progress in the connected account' and describes idempotency ('repeating the same item and status preserves the completed timestamp and returns the saved state'). This enriches the destructiveHint with concrete consequences.

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?

Four sentences that are dense but each earns its place, with the core action front-loaded. No wasted filler, though slightly long for such a simple tool.

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 3-param mutation with an output schema, the description covers the action, precondition, side effects, idempotency, and return behavior. An agent has everything needed to call it correctly.

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 0%, so the description must carry the burden. It explains the status values (done, to do, not applicable), constrains item_id to the exact user-selected ID, and implies the confirmation requirement that maps to the `confirmed` const. It stops short of detailing the item_id format or why `confirmed` must be true.

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/action (save done/todo/na) on a specific resource (an item from an Afterglow checklist), scoped to 'the exact item ID the user selected.' This clearly distinguishes it from the read-only sibling get_checklist.

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?

Gives a clear precondition: 'Obtain confirmation of the item and status before calling.' It implies usage context (user-selected item) but names no explicit alternative or when-not condition, so it falls short of a 5.

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