Update a calendar event

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

The annotation set says the tool is not read-only and is idempotent, but the description goes beyond annotations by disclosing a crucial behavioral nuance: the update is partial, and passing attendees replaces the full guest list. It also explains why start and end must be paired. This adds real value beyond the structured data.

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 entire description is three sentences with zero filler. The most important fact ('only the fields you give are touched') is front-loaded, and the start/end pairing and attendee replacement exceptions are stated precisely without redundant elaboration.

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 12 parameters, the description covers the critical behaviors that could cause incorrect parameter usage: partial updates, paired temporal fields, and attendee list replacement. The remaining parameters are adequately documented by the complete schema, and no output schema is expected for an update operation. It is comprehensive enough without being verbose.

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?

The input schema covers all 12 parameters with 100% coverage, so the baseline is 3. The description adds cross-parameter meaning: the partial-update behavior for all fields and the attendee replacement semantics. While some of this is echoed in the schema, the description frames it as tool-level behavior, which is useful.

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?

Begins with a specific verb-plus-resource statement ('Change an existing event'), clearly distinguishing this from calendar_create_event and calendar_delete_event. It also adds partial-update semantics ('Only the fields you give are touched'), which sharpens what the tool does.

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 description clearly establishes the context for use — modifying an existing event — and adds important constraints such as start/end pairing and attendee replacement. It does not explicitly name sibling alternatives or state when not to use it, but the usage context is concrete enough for an agent to select it.

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