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

Goes well beyond the annotations: it discloses that capacity and fee limits are not enforced, that no payment is processed, and that no confirmation e-mail is sent — exactly the side-effect boundaries an agent needs before firing a write. It also names the backing API (APIv4 Participant.create), confirming the mutation is a single-record create.

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 with the write nature front-loaded, then the exclusion list, then the API reference. No filler and nothing buried.

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 mutation tool with no output schema, it covers scope, non-enforced checks and side effects thoroughly. The only omission is what comes back (e.g. the new participant id), which would help an agent chain a follow-up call.

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 event_id, contact_id, role, status and source are already documented in the schema. The description only implies the two required ids via 'ONE contact for ONE event' and adds no extra meaning for role/status/source, so the baseline 3 applies.

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 ('registers ONE contact for ONE event') and pins down cardinality and the underlying object (a participant record). This clearly separates it from civicrm_list_participants and the contact-creation siblings.

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 negative scoping ('does not take payment', 'sends no confirmation e-mail') tells the agent when this tool alone is insufficient, implying record_contribution is needed for fees. It stops short of naming the alternative tool or stating prerequisites (e.g. event/contact must exist first), so it falls just below a 5.

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