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

Beyond annotations (readOnly=false, dst=false, idempotent=false), it discloses the concrete side effect: a confirmation email with a QR ticket is sent, unless the organiser disabled it. It also discloses the important default that registration does NOT subscribe the person to marketing unless marketingOptIn is explicitly true — exactly the kind of consequence an agent cannot get from structured fields.

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 tight sentences, front-loaded with purpose and then the side-effect/opt-in caveats. The middle sentence is slightly convoluted ('unless the organiser switched it off, so confirm...'), but nothing is 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?

With no output schema and annotations covering only the safety profile, the description does well on side effects but leaves the return value (e.g., registration confirmation/ID) and most of the eight inputs unexplained. Adequate for calling the tool correctly on the required fields, incomplete for the optional ones.

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 only 38% and six of eight parameters (city, company, firstName, lastName, email, apiKey) get no explanation here. The one parameter it addresses, marketingOptIn, only restates what the schema description already says ('Only when the person asked to hear about future events'), so it adds little meaning beyond the schema.

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 first sentence states a specific verb and resource ('Register someone for an event'), which is clearly distinct from read-side siblings like list_event_registrations and check_in_attendee. However, it never names or contrasts with those siblings, so an agent must infer the boundary itself.

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 provides a prerequisite ('confirm the person and the event with the user first') and a conditional for marketingOptIn, which is real guidance. But it never states when to use this tool versus near alternatives such as check_in_attendee or send_event, so routing is left implied.

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