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

Annotations already declare non-read-only, non-destructive, non-idempotent, closed-world behavior. Beyond that, the description discloses non-obvious semantics: cleanup minutes are held free after the service, and existing appointments retain the name and price they were booked with, i.e. updates are not retroactive.

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 dense sentence that front-loads the add/update purpose and then the three configurable fields, closing with the historical-booking caveat. No filler and nothing redundant with the schema.

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 4-parameter mutation tool with no output schema, the description covers purpose, the upsert key, field meanings, and the persistence behavior of existing bookings. It omits only peripheral details such as permission requirements and what happens when cleanup_minutes is omitted on update.

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 only 25% (only 'price' is documented), so the description must compensate. It does: it defines minutes as service length, price as dollars, and cleanup_minutes as free buffer time after the service, which the schema leaves unexplained.

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 ('Add a service clients can book, or update one with the same name') and captures the upsert semantics keyed on name. This clearly separates it from siblings like remove_calendar_service, set_calendar_hours, and update_calendar_settings.

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?

The description tells the agent the key usage rule: call it to create a service, or to update one by passing the same name. It gives clear context for when the tool applies but names no alternative or exclusion (e.g., no pointer to remove_calendar_service for deletion).

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