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

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful non-annotation context: this is a partial update where 'only the fields you pass change'. It does not mention permission requirements or failure behavior for an invalid id, and 'PUT' sits awkwardly beside the claim of partial-update semantics.

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?

Three short fragments, zero filler, with the WRITE marker and the resource front-loaded. The partial-update constraint and the one high-value parameter hint are packed into the minimum space.

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 an 8-parameter mutation tool with full schema coverage and annotations covering read/write, idempotency and destructiveness, the description supplies what the structured fields cannot: that the operation is a merge-style partial update. No output schema exists, but nothing about calling it correctly is left unknown.

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% (8 of 8 params documented, including the task-vs-event distinctions on due_date/start_time/end_time), so the baseline is 3. The description's only parameter note, 'Pass complete: true to mark a task done', merely restates the schema text and adds no new meaning.

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 and resource ('WRITE: change a task or event') and pins the endpoint ('PUT /calendar_entries/{id}'), which is enough to separate it from the read siblings get_calendar_entry/list_calendar_entries. It never names create_calendar_entry or update_* siblings explicitly, so the differentiation is implied rather than stated.

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?

Usage is only implied: an agent can infer this is for modifying an existing entry because an id is required. There is no explicit statement of when to prefer this over create_calendar_entry, get_calendar_entry, or the other update_* tools, and no prerequisites (e.g. entry must already exist).

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