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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds real value beyond that: the return shape ('open start times ... per provider') and an auth precondition ('Needs the user's Cotlet API key with access to this app'). It stops short of describing result limits or pagination.

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?

The first two sentences are near-duplicates ('Open slots for a service ... in a date range' / 'Returns open start times for one service in a date range, per provider'), so one sentence of the short description is largely wasted. The remaining routing and auth sentences do earn their place.

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 read-only search with no output schema and annotations that carry the safety profile, the description covers purpose, scope, return content, downstream usage, and the auth requirement. Only pagination/result-volume behavior is left unstated.

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 five parameters are documented in the schema. The description only restates that provider is optional and the scope is a date range, which adds marginal semantics; the 3 baseline applies 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 names a specific verb and resource ('Open slots for a service') plus the scoping dimensions (single service, optional provider, date range). An agent can distinguish it from vagaro_list_appointments or vagaro_book_appointment without opening a 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 explicitly routes the agent downstream: 'Use a start from the result in book_appointment or reschedule_appointment so the booking lands on a free slot.' It gives clear context for the tool's role in the booking flow, but offers no explicit when-not-to-use guidance versus sibling availability/list tools.

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