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

Annotations cover safety (destructiveHint=false, idempotentHint=true), but the description adds high-value context beyond them: it does NOT send an email, and it explains the dedup mechanism (same email/phone, or same name absent conflicting contact details) and that the existing participant is returned. This turns a bare idempotency hint into an actionable retry guarantee.

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 dense sentences, front-loaded with the core action, then params, then the no-email caveat and retry semantics. No filler; each sentence carries distinct information.

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 an output schema (return values needn't be explained) and full annotation coverage, the description supplies the missing pieces: side-effect disclosure (no email), routing to the alternative, and idempotency behavior. Nothing essential for correct invocation is absent.

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 0%, so the description must compensate, and it does: it enumerates id (trip uuid) plus body fields displayName (required), email, phone. It conveys requiredness and the uuid nature of id, though it adds no format or validation nuance beyond what the schema enforces.

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 a participant to a trip') and explicitly differentiates from the sibling invite_trip_participant. An agent can distinguish the manual-add path from the invite path without opening the schema.

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?

Names the alternative (invite_trip_participant) and the exact condition that selects it ('for an invite link'). The manual vs. invite distinction is stated, leaving nothing to inference.

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