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

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=false, and openWorldHint=true, so the agent knows this is a non-idempotent write. The description's 'WRITE:' prefix largely restates that, and it adds only the conflict-checking advice; it does not explain side effects such as calendar conflicts, notification behavior, or what happens on retry.

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 with the write nature and the resource front-loaded, then the precondition, then the endpoint. Nothing is wasted, though 'POST /lessons' is mild filler for an agent that already has the tool selected.

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 tool with no output schema, the description covers the core intent and one important precondition, but omits notable behaviors: group-lesson semantics tied to `spaces`, whether the response returns a new lesson id, and how defaults (name, to_date, time_zone) are resolved.

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 92%, so nearly every parameter is already documented, including defaults and formats (guarded times, dates, time_zone). The description's phrase 'one or more students with a teacher, service and location' loosely maps to student_ids/employee_id/service_id/location_id but adds no new semantics, so baseline 3 is appropriate.

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 and resource ('schedule a single lesson on the calendar') plus the key entities involved (students, teacher, service, location). It is immediately distinguishable from siblings like teachworks_add_student_to_lesson or teachworks_create_payment.

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?

Explicitly tells the agent to call teachworks_list_availabilities and teachworks_list_lessons first to avoid conflicts, which is real operational guidance. It stops short of naming when NOT to use this tool (e.g., adding a student to an existing lesson) or stating the precondition that a lesson would otherwise be double-booked.

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