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

Substantially exceeds the annotations. readOnlyHint=false and idempotentHint=false only signal 'has side effects, not repeatable'; the description adds the critical nuance that nothing is written until the user taps Add, that a Keeploop notification is sent, that proposals expire in 24 hours, and that a Pro subscription is required. This is exactly the kind of behavioral context annotations cannot express.

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?

Five sentences, each earning its place, front-loaded with purpose followed by behavior and then the parameter rules. No filler or restatement of the title.

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?

Given an output schema exists, the description needn't explain returns, yet it still notes 'Returns busy events it overlaps' for conflict awareness. Combined with the write-deferral semantics, expiry, and Pro gate, an agent has everything needed to invoke this correctly.

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 0% across 8 params, so the description must compensate. It does document the calendar param (title or id, defaulting to the user's default), the end/duration_minutes relationship, and the no-attendees constraint, but leaves start format, all_day, location, and notes entirely unexplained. Partial compensation only.

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+resource ('Propose adding an event ... to the user's calendar') and immediately scopes it with the 'no attendees' qualifier, which cleanly separates it from sibling write/notify tools like send_email or propose_reschedule. An agent can identify the operation without opening the schema.

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 clear operational context: the proposal flow (notification, tap-to-Add), the 24-hour expiry, the Pro requirement, and the end-or-duration_minutes rule. It stops short of explicitly naming alternatives such as propose_reschedule or its cancel_proposal counterpart, so it informs without routing.

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