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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and closed-world, so safety is covered. The description adds genuinely new behavioral context: this renders a visual, interactive surface (a timeline the user can scroll and add to) rather than returning plain data, which is not derivable from the annotations. It stops short of mentioning permissions or what happens to the underlying data, keeping it at 4.

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 sentences, zero filler. The purpose and visual nature come first, then the usage trigger, then the alternative — well front-loaded and appropriately sized for the tool's complexity.

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 tool has an output schema, so return values need not be explained, and the description covers purpose, content, trigger and the alternative tool. Nothing an agent needs to select and invoke this correctly is missing.

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 100% and all three parameters (date, babyId, timezone) are documented with defaults and formats in the schema itself. The description adds no parameter-level meaning beyond what the schema provides, so the baseline of 3 applies.

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 (show) and resource (one day for a baby), enumerates the content displayed (total sleep, feeds, nappies, scrollable timeline), and explicitly names the sibling it is not (get_day_summary). An agent can distinguish it from list_* and get_day_summary without opening any schema.

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 an explicit trigger ('when the user asks to see, show or open their day or timeline') and an explicit exclusion with the alternative to use instead for non-visual answers ('For a plain answer without a visual, use get_day_summary'). Both when-to-use and when-not-to-use are covered.

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