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

Annotations already establish this is a non-readonly, non-destructive, non-idempotent, closed-world mutation. The description adds genuinely non-structured context: terminal states are irreversible here (CRM-21), which fields each mode demands, and an explicit 'Effects' line summarizing the resulting state and that the reason is retained.

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?

Front-loaded with the mode enumeration, then the requirements, then effects — a sensible order. Some space is spent on aphorism ('an event with no outcome is an intention that went stale') that conveys tone more than callable information, but the core content 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?

For a 12-parameter mutation with no output schema and adequate annotations, the description covers the decision-relevant surface: how to pick a mode, what each mode requires, and irreversibility. Minor gaps remain on the auxiliary fields (title, location, url, note) and on what the response returns.

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 description contributes one real cross-field constraint the schema cannot express: a date move requires both reason and source together. However, with coverage at 67%, four parameters (url, note, title, location) have empty schema descriptions and are never addressed in the prose, so compensation is only partial.

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 (update) and resource (event) and enumerates the four modes it covers: reschedule, correct, close as done, cancel. It also distinguishes itself from the create path by noting that a resurrected cancellation 'is a new event with a new source', though it does not name crm_add_event or crm_attend_event directly.

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?

Gives per-mode preconditions with a concrete example of good vs. bad input ('the venue page now says the 14th' vs 'moved') and a clear when-not: cancelled/done cannot be undone here, so reopen by creating a new event. It stops short of naming the sibling tool to use for that create path, leaving a small inference step.

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