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

The description thoroughly explains the idempotency behavior: 'Pass idempotencyKey to make retries safe — same key + same body returns the original response, same key + different body returns IDEMPOTENCY_BODY_MISMATCH 409.' It also discloses a subtle caveat about partial failure with address attachment, going beyond the basic idempotentHint annotation.

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?

The description is four sentences, each serving a clear purpose: purpose, use case, alternative guidance, and idempotency note. It is succinct, front-loaded with the primary action, and contains no redundant or filler text.

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?

The description covers all essential contexts: what the tool does, when to invoke it, how it differs from related tools (agent_update for adding addresses later), and important behavioral nuances (idempotency and partial-failure caveat). Since an output schema exists separately, the lack of return-value details is acceptable.

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?

The schema already provides detailed descriptions for every parameter (100% coverage), and the overall description adds high-level context (e.g., 'sending identity or automation actor') that is not in the schema. However, it does not individually elaborate on each parameter beyond what the schema states, so a score slightly above the schema-heavy baseline is warranted.

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 clearly states the tool's purpose: 'Create a new agent with optional metadata, and optionally attach an initial address.' It also identifies the intended use case ('provisioning a new sending identity or automation actor'), making the action and scope unmistakable.

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 description explicitly says when to use this tool and when not: 'Use this when provisioning a new sending identity or automation actor' and 'To add more addresses later, use agent_update.' This provides direct guidance for tool selection among siblings.

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