create_event

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

Annotations already indicate this is a mutating, non-idempotent operation, but the description adds meaningful context beyond those flags: the feature is experimental, sync is client-side, and the event will not sync onward unless the Marvin app is running. This is useful behavioral information that annotations cannot convey.

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 text is short and front-loads the experimental warning, but it repeats the same information: 'Create a calendar event (experimental)' is immediately followed by 'EXPERIMENTAL: Create a calendar event.' The redundancy prevents it from being as tight and efficient as it could be.

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?

With complete parameter documentation and an output schema available, the description covers the one critical piece of context that could surprise an agent: the dependency on a running client app for external calendar sync. It does not mention alternative behavior or failure modes, but the structured data covers the remaining essentials.

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%, and each parameter already has an explicit description, including an ISO 8601 example for start_iso and minimum constraints for length_minutes. The tool description adds no extra parameter-level detail, so the baseline 3 applies.

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 direct action ('Create') on a defined resource ('calendar event') and marks it as 'experimental.' It clearly distinguishes this from sibling tools like create_task and create_time_block by specifying the calendar-event context and external-calendar sync. No ambiguity remains about 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 gives a clear operational prerequisite: the Marvin app must be running on some device for the event to sync to an external calendar. However, it does not compare this tool with siblings such as create_time_block, nor does it state when to prefer or avoid this tool. Usage is mostly implied by the resource name and purpose.

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