Write the day's note

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

Goes well beyond the annotations: it discloses the destructive edge case ('' deletes the note), what is preserved (tags and everything else of the day), and return semantics (data.previous for undo, data.ok confirming a re-read). This is exactly the added context destructiveHint/idempotentHint cannot convey.

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 tight sentences, front-loaded with the action and the destructive case, then the preservation and return facts. Every clause carries information; nothing is padding.

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?

Annotations, a full-coverage schema, and an output schema already cover safety and return shape; the description still adds the undo value (data.previous) and the verification signal (data.ok), leaving nothing an agent needs to call this correctly unspecified.

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%, so both parameters are already documented in the schema, including the get_day/get_today usage hints. The description restates the '' -to-delete behavior and the 'get_day's note' input convention but adds no syntax or format detail beyond the schema, so baseline 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+resource+scope: 'Replace the user's note for a diary day ... with note', and clarifies the delete semantics of an empty string. It anchors itself relative to sibling get_day, so an agent can immediately distinguish it from the read-side note tools.

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 clear operational context: an empty note deletes, tags and other day data are untouched, and get_day's note is the input to extend. Schema adds the today/yesterday resolution path via get_today. No explicit when-not or named alternative, since there is no competing write-note sibling, so 4 rather than 5.

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