List Inboxes

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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds valuable context by clarifying that results are scoped to the API key and that each entry includes UUID, email, display name, provider, optional brand, and capabilities—information that helps an agent select the correct inbox_id.

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?

Two sentences with no wasted words. The purpose is front-loaded, the critical 'call it FIRST' instruction is prominent, and the output payload is summarized efficiently without reproducing the schema.

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 is complete for a simple read-only list tool with an output schema. It explains the tool's purpose, when to use it, what the response contains, and how the response relates to other tools. Nothing essential is missing for an agent to invoke it correctly.

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 100%, and the schema already documents provider and include_capabilities well. The description does not add new param-level meaning beyond mentioning the capabilities object in the response, but it does not need to because the schema carries the load.

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 states a specific verb and resource: 'List every inbox (mailbox or account) this API key may use.' It clearly distinguishes the tool's role from siblings by positioning it as the entry point that supplies the inbox_id for other tools. Each output field is listed, so an agent knows exactly what to expect.

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 to 'Call it FIRST for the inbox_id the other tools take,' giving clear contextual guidance on when this tool should be used. It does not discuss when not to use it or name alternatives, but no sibling serves the same discovery/list role, so this level of guidance is sufficient.

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