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

Annotations already declare readOnlyHint=false, idempotentHint=false, openWorldHint=true and destructiveHint=false, so the write/external-effect profile is covered structurally. The description adds almost nothing beyond that: it does not warn that inviting attendees sends notifications, that no dedup/idempotency guard exists, or what happens if start/end are omitted — a notable gap for a 14-parameter mutation.

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 action, then the required inputs, then the format hint. The ISO 8601 sentence is mildly redundant with the schema's own ISO 8601 descriptions, so it is not perfectly waste-free, but the definition is tight and readable.

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 14-parameter, nested-object tool with no output schema and zero required fields, the description omits meaningful capabilities: calendar_id targeting, timezone handling for offset-less times, and Google Meet creation via add_google_meet/conference_data. Schema coverage is complete enough that an agent could still call it, but the description gives no hint that these features exist.

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%, including aliases, timezone semantics, and the end-defaults-to-start+1h rule, so the schema does the heavy lifting. The description repeats only title/start/end/attendees and the ISO 8601 shape, adding no meaning the schema does not already carry — the baseline 3 for high coverage is correct.

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 ("Create a new event in Google Calendar") and enumerates the core inputs, so an agent can immediately tell it apart from calendar_update_event or calendar_delete_event. It stops short of naming any sibling explicitly, which is the only thing keeping it from a 5.

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 by the verb: you call this when you want a new event created. There is no statement of when to prefer this over calendar_update_event (existing event) or calendar_check_availability (scheduling), and no prerequisites such as calendar access or attendee invite notifications.

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