update_event

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

With no annotations, the description carries the full burden and does well: it discloses partial-update semantics, that attendees replaces the entire list, the feature-flag gate that can cause refusal, and the notification caveat that guests may still be emailed. Missing are permission requirements and what an invalid event_id produces, but the risky behaviors an agent must know before mutating data are covered.

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 sentences, front-loaded with the core semantics, then the sharpest edge case, then the external side effect. 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?

For a mutation tool with no annotations, no output schema, and 9 undocumented parameters, the description covers mutation semantics and side effects but leaves parameter formats and failure modes unexplained. Adequate, not complete.

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 0% across 9 parameters, so the description must compensate and only partly does. It clarifies the two most consequential semantics (nulls mean 'unchanged', attendees is a full replacement), but start/end string formats, time_zone, and calendar_id defaults remain undocumented anywhere.

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+resource ('Change fields on a calendar event') that cleanly separates it from create_event and get_event in the sibling list. It doesn't name a sibling explicitly, but the partial-update framing makes the distinction obvious.

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?

It implies when this tool applies via 'omitted fields stay as they are', which tells the agent to use it for partial edits rather than full rewrites. It also states the condition under which attendees is refused (DRAFT_ONLY_GOOGLE_ALLOW_ATTENDEES off). There is no explicit guidance on choosing this over create_event or update_draft, so usage is implied rather than directed.

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