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

The description thoroughly explains the side effects: writing a 0-kcal food_log entry for 'fast', leaving the day blank for 'forgot', and clearing both for 'unanswered'. It also notes that it refuses to touch days with real meals. This goes beyond the annotations (readOnlyHint=false, destructiveHint=true) by detailing exactly what changes occur to the data.

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?

The description is clear but somewhat repetitive, repeating the three-state definitions twice and the 'setting one clears the other' rule twice. It could be tightened without losing meaning, but it remains organized and not excessively verbose for the complexity of the 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?

The description covers prerequisites (use list_meals first), parameters, exact effects, and failure conditions (refuses days with real meals). It even notes that the tool is for chat usage instead of the in-app prompt. No critical context is missing for an agent to invoke this tool 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?

Both parameters (date, answer) are described in the schema with full coverage. The description further elaborates on the 'answer' enum values—'fast' means intentional 0-calorie day, 'forgot' means day stays excluded, 'unanswered' clears any prior answer—adding richer semantics beyond the schema's basic descriptions.

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 clearly states the tool's action: 'Set, change, or undo the answer to why is this day empty?' It specifies the resource (a date) and the exact states (fast, forgot, unanswered) it manages. It also distinguishes itself as the only way to move between these states, making its purpose 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?

Explicit usage guidance is provided: 'Use when the user wants to flip a fast day to forgotten (or back), or undo either one, in chat instead of the in-app prompt.' It also advises to 'Use list_meals first if unsure whether the date already has real food logged' and mentions refusal when real meals exist, giving clear when-to-use and when-not-to-use instructions.

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