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

Annotations already declare this is a non-readonly, non-destructive, non-idempotent, open-world mutation. The description adds a genuinely useful behavioral rule (source the data from the user, don't fabricate it), which goes beyond annotations. It does not, however, warn about the non-idempotent trait the annotations flag — repeated calls may add duplicates — nor mention permissions or the mutation's effect.

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 short sentences, front-loaded with the action. Slight redundancy between 'Ask the user — never choose for them' and 'come from the user,' but nothing wasted and no padding.

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 6-parameter mutation tool with 50% schema coverage and no output schema, the description covers the core action and a data-sourcing rule but omits the add_booking_guests distinction and says nothing about what the call returns or failure modes. Adequate but with clear gaps given the sibling overlap.

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 50%: bookingUid, timeZone and language are documented, while name, email and phoneNumber are bare. The description's line about name/email/time zone coming from the user gives a sourcing hint but no format or semantics beyond what the schema already says. Baseline 3 fits given partial coverage.

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+resource: 'Add an attendee to a booking.' That's clear on its own. But the sibling set contains add_booking_guests, a near-identical operation, and the description does nothing to distinguish the singular attendee tool from the plural guests tool, leaving a real selection ambiguity.

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 implied (to attach someone to a booking), and 'Ask the user — never choose for them' is useful guardrail guidance. However there is no when-not guidance and, critically, no routing against add_booking_guests, which is the closest alternative an agent would hesitate between.

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