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

Annotations only say readOnly=false, destructive=false, openWorld=true. The description adds substantive behavioral context beyond that: the action is reversible via host reinstatement, each call is confirmed by default (and this can be toggled off), the call reaches other people and therefore needs user confirmation, and it requires an API key with app access. This is exactly the extra context annotations can't carry.

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 purpose is front-loaded, but the text repeats itself: reinstatement is stated twice ('Evite lets you reinstate it' and again 'The host can reinstate the event ... before its original date'), and the confirmation requirement is stated twice as well. Trimming the duplication would improve it without losing information.

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 no-output-schema mutation tool with annotations already covering the safety profile, the description supplies the missing pieces: reversibility, confirmation behavior, audience reach, and auth requirements. It is nearly complete; only explicit sibling routing is absent.

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 coverage is 100%, so the baseline is 3, but the description genuinely adds meaning for the message parameter by explaining the condition under which it should be supplied (guests may not get an automatic cancellation notice). That elevates it above the schema-only baseline.

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 states a specific verb+resource (cancel an event) with a scope constraint (before its date) and an optional payload (a note to guests). That is far more precise than a tautology. It does not, however, explicitly differentiate itself from siblings like evite_update_event or evite_duplicate_event, so it stops short of 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?

It gives clear conditional guidance for the optional message ('pass message when they should hear it' because Evite doesn't guarantee an automatic guest notice) and states that reinstatement is possible before the original date. It does not name an alternative tool or state when NOT to use this one, so it lacks the explicit routing of a 5.

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