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

Annotations already indicate this is not read-only, but the description adds important behavioral context: the tool draws from the student's open package when one exists, and prior confirmation is required. This goes beyond the structured annotation fields without contradicting them.

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, each carrying useful information, with no filler. The key action and prerequisites are front-loaded, and the package behavior is stated compactly.

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 tool with three documented parameters and no output schema, the description plus schema covers the action, preconditions, source of inputs, and a key side effect. It does not describe return values or error cases, but those are not required for this straightforward booking tool.

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. The description adds extra meaning by specifying that startsAt must be a free start and that the token belongs to an accepted student, and it clarifies the package-drawing behavior. This adds value beyond the schema descriptions.

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 action ('book one lesson'), a specific target ('an accepted student'), and a precise constraint ('at a free start'). It clearly distinguishes itself from siblings like cancel_lesson, coach_slots, and request_coach by focusing on the booking action and the accepted-student token context.

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 implies the correct context: use it only after the student is accepted, with a start from coach_slots, and after confirming the time with the person. It gives a clear prerequisite ('Confirm the time with the person first') but does not explicitly name alternatives or say when not to use it.

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