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

Annotations already declare a non-read-only, idempotent, open-world, destructive operation, so the agent knows the safety profile. The description adds a useful side-effect clarification ("Does not trigger more emails") and the confirmation precondition, but says nothing about what state is mutated, whether duplicates are tolerated, or what errors look like — notable given the destructiveHint.

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 purpose, then the precondition, then the side-effect caveat. 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?

This is a five-required-parameter mutation tool with no output schema and a destructive annotation, yet the description explains none of the identifiers or the version/requestId semantics needed to call it correctly. The precondition and email caveat are good, but the definition is not complete enough for a tool of this complexity.

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% across six parameters, so the description carries the full burden and provides no meaning for eventId, participantId, requestId, channel, version, or agent. An agent must infer the format constraints (48-hex eventId, UUID participantId, 8-char minimum requestId, bounded version) entirely from the raw 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 description uses a specific verb and resource ("Record a successful external message delivery") that clearly identifies this as a write-side completion record. It does not, however, distinguish itself from the sibling get_channel_update, which an agent could easily confuse with it.

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?

"Only call after your channel confirms the message was sent" gives an explicit precondition for invoking the tool. There is no statement of when not to call it and no named alternative, so it stops short of full routing guidance.

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