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

Annotations already declare readOnlyHint/openWorldHint, so safety is covered. The description adds real value beyond them: the ordering of returned appointments ('newest first') and the authentication prerequisite ('Cotlet API key with access to this app'). It does not describe pagination or result limits.

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?

Front-loaded lead sentence is good, but the definition then repeats itself: 'contact details, notes and appointment history' is immediately re-phrased as 'contact details, notes and past appointments, newest first'. One of those two sentences is largely redundant.

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?

With no output schema, the description correctly takes on the burden of describing the returned card and its contents, and it discloses the auth requirement. It is adequate, though a note on behavior when neither ID nor email is supplied (both params are optional) would close the remaining gap.

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% and the schema already explains that email substitutes for ID. The description's 'by ID or by email' restates that they are alternatives without adding syntax or validation detail, so it sits at the baseline.

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 ('One client card'), and enumerates what it contains: contact details, notes, appointment history. It implicitly contrasts with the plural list tool by emphasizing 'One client card', but never names booksy_list_clients or booksy_add_client explicitly.

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?

Says how to look up the client ('by ID or by email'), which is closer to parameter guidance than usage guidance. There is no statement of when to use this versus booksy_list_clients or booksy_get_appointment, so routing must be inferred.

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