list_emails

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

Goes well beyond readOnlyHint/idempotentHint. It discloses what the call returns (envelope summaries + uidvalidity), preserves ordering, and exposes a thoughtful security property: message fields are unreliable and must be treated as untrusted data. This is rich, behavior-behavioral context an agent needs before invoking the tool.

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 deliberate, dense sentences: operation and order, return content and output contract, then pagination guidance and safety warning. Each sentence earns its place; the most important behavioral facts are front-loaded without redundancy.

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?

Given a 6-parameters tool with an output schema and readOnly/idempotentHint annotations, the description is sufficiently complete for correct invocation. It doesn't need to restade the output schema, and the security caveat is critical context that rounds out the behavioral picture. Minor lack of explicit sibling routing is covered by clear folder semantics.

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%, so the baseline for parameter semantics is 3. The description reinforces pagination behavior ('Page with next_before_uid rather than offset') and implies correspondence between pages, but this already appears in the schema. No significant semantic addition is made beyond the structured parameter docs.

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?

Description states a specific verb andresource: 'List messages in a folder, newest first, with pagination.' It clearly conveys folder-scoped list behavior, and the reference to envelope summaries distinguishes it from folder-level tools like list_folders. It doesn't explicitly name siblings or draw exclusionary boundaries with search_emails, so it stops short of full distinction.

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 gives concrete guidance: 'Page with next_before_uid rather than offset so newly arrived mail cannot shift the results'. This is clear about preferred pagination approach and even reasons about stability. It does't explicitly say when to choose this over search_emails or how to integrate with list_folders, but the folder-based framing implies the intended use fairly well.

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