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

readOnlyHint=true already tells the agent this is a safe read. The description adds useful context by naming the returned fields and the underlying endpoint, but says nothing about pagination, result caps, or what happens when both event_id and contact_id are supplied.

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?

One front-loaded sentence covering the two use modes plus a short endpoint reference — no filler or repetition.

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 five optional parameters, the agent gets no guidance on whether one of event_id/contact_id is required, how results are paged, or what an unfiltered call returns. Adequate for a simple list tool but leaves real gaps.

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%, so the schema already documents all five parameters. The description echoes the event/contact duality and mentions waitlist, adding only marginal meaning beyond the schema's own descriptions.

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 ('List registrations for an event... or for a contact') and enumerates the fields returned (registration type, fee, paid, checked in, waitlist). This clearly separates it from siblings like list_event_registration_types and create_event_registration.

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 two-mode framing (by event = attendee list, by contact = their signups) implies when each parameter applies, but it never states when to reach for this tool versus list_events or get_event, nor any prerequisites. Usage is implied rather than prescribed.

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