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

Annotations already declare write, idempotent, destructive and open-world; the description adds genuinely new behavior: partial-update semantics ('only the fields you pass are changed'), a concrete return value ('returns the updated day'), and the underlying GraphQL mutation name. It restates idempotency rather than explaining it, so a small deduction.

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?

One short paragraph, front-loaded with the operation type, then the id prerequisite, then field semantics, then return value. No sentence is filler.

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?

Covers everything an agent needs to call it correctly: how to get the required id, that unpassed fields are untouched, the result shape, and the underlying API operation. No output schema exists, and the description supplies the return value it would otherwise lack.

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% – formats, enum values, and max lengths for all six parameters are already documented. The description's 'only the fields you pass are changed' adds mild meaning about optionality, but otherwise repeats the field list without new constraints.

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?

Starts with 'WRITE: change an existing timesheet entry' – a specific verb plus resource – and enumerates the mutable fields (times, part of day, project, note), which cleanly separates it from kiwihr_create_timesheet_entry and kiwihr_delete_timesheet_entry among the siblings.

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?

Explicitly routes the agent to kiwihr_get_timesheet to obtain the entry_id, which is the main prerequisite. It does not spell out when to prefer this over create/delete siblings, but that is largely self-evident from the verb.

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