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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds useful scope context (availability is limited to Laurie's private session offerings), but says nothing about timezone handling, whether slots are cached or live, or how results are bounded by the days/from_date window.

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?

A single front-loaded sentence that states the resource and scope with no filler. The service enumeration is somewhat long but it conveys real domain vocabulary an agent may need to match caller phrasing.

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 simple read-only lookup with full schema coverage, the definition is adequate but thin. With no output schema, the description could have said what an 'open time' looks like (date, time, slot length, timezone) and whether an empty result is possible; instead the agent must discover the return shape empirically.

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%, so all three parameters (days, service, from_date) are already documented in the schema with defaults and formats. The description adds no constraint or format detail beyond listing example service names, so the baseline of 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 gives a specific verb+resource ('Returns open times for a private session with Laurie') and enumerates the service types, which implicitly distinguishes it from the class-oriented siblings like get_class_schedule. It stops short of explicitly naming book_session or list_services as the companion tools, so the differentiation is inferred rather than stated.

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?

Usage is only implied: an agent can infer this is the availability check that precedes book_session, but the description never says when to use it versus get_class_schedule or how it relates to list_services. No prerequisites, exclusions, or alternative routing are stated.

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