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

Annotations already declare readOnly/idempotent/non-destructive, so the description is free to add behavior they cannot express: counting includes all booking statuses, the window is capped at 31 days, the default window is the next 7 days, and counting stops at 100. The result cap and default window in particular are operationally important and appear nowhere in the annotations.

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 sentences, trigger condition front-loaded first, followed by scope/limits and then negative scope. Every clause carries information (window limit, default, cap, exclusions) with no filler.

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?

An output schema exists, so return-shape explanation is unnecessary; the description instead supplies the behavioral facts an output schema cannot (per-UTC-day aggregation, status-agnostic counting, 100-count cap, 31-day window). Nothing needed to call it correctly is missing.

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 description coverage is 100%, and the schema already documents startTime/endTime defaults and the 31-day constraint, so the description contributes no additional parameter detail beyond what the agent will read anyway. Baseline 3 is appropriate when the schema does the heavy lifting.

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 pairs a concrete verb and resource ('Returns booking counts per UTC day for one gym') and constrains the scope ('whatever their status', 'any window of at most 31 days'). Combined with the title, an agent can distinguish this from get_gym_availability or get_gym_payment_summary without opening any 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?

It gives an explicit trigger ('when someone asks how busy their gym is or how many appointments or sessions are booked each day, past or upcoming') and explicit exclusions ('Not for counting cancellations or seeing which members are booked'). It stops short of naming which sibling to use instead for those cases, so it is clear context without full alternative routing.

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