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

The annotations declare readOnlyHint=false, destructiveHint=true and openWorldHint=false, so the safety profile is already known. The description adds what the annotations cannot: that the write is limited to the caller's own record, that it can be undone from the same surface, and that it returns an ordinary result rather than a plan_token. It does not contradict the annotations; the undoability note moderates the destructive hint rather than denying it.

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 structure is front-loaded: the operation and its field list come first, then scope, then the confirmation policy. The CONFIRMATION block is longer than strictly needed and repeats 'it writes only their own record', which appears in spirit earlier. No sentence is wasted, however, and the caller-action framing earns its place.

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?

With nine parameters, 11% schema coverage and no output schema, this is a demanding definition, and it covers most of what an agent needs: the editable field set, time format, ownership scope, and confirmation semantics. It leaves open the timezone assumption for ISO 8601 values and the behavior when a value is rejected, which would matter for a write tool an agent may call without a confirmation step.

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 only 11%, so the description has to compensate, and it does: it names all eight optional fields and adds 'Times are ISO 8601', which the schema does not state. It also clarifies that event_id addresses only the caller's own events. It still says nothing about timezone handling, whether the update is partial or full replacement, or the 255-character limits.

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 opens with a specific verb and resource, 'Edit fields of one of the caller's calendar events by id', then enumerates exactly which fields are editable. It scopes the operation to the caller's own records, which separates it from an administrative edit. It never distinguishes itself from close siblings such as create_event, delete_event, get_event or the plural update_events, so it stops short of full sibling differentiation.

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?

The CONFIRMATION paragraph gives real usage context: this tool runs immediately when the caller asks for it, and the caller can undo the change from the same surface. It also states the boundary that destructive, outbound and financial actions still propose and wait. What it does not do is route the agent between alternatives: it never says when to use create_event instead, what update_events does differently, or what makes this a bad choice.

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