List Thread Messages

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorld, so the safety profile is fully covered by structured data. The description adds no behavioral context of its own, such as pagination behavior, default result size, or what happens when thread_id is unknown or inaccessible.

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 short sentences with the primary action front-loaded and no filler. The second sentence is slightly imprecise ("message body tools" is undefined), which costs a point but the overall shape is efficient.

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?

An output schema exists, so return values need not be explained, and the schema covers all five parameters. What remains unaddressed is the listing behavior itself — pagination defaults, ordering, and scoping across multiple mailboxes — leaving the definition adequate but thin for a paginated list tool.

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 every parameter — sort, limit, cursor, thread_id, mailbox_id — is documented in the schema including the multi-mailbox targeting caveat. The description contributes nothing beyond that, so the baseline of 3 applies.

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 messages inside a known thread," which is distinct from thread-level retrieval (get_thread) or mailbox-wide listing. It implicitly differentiates itself from body-fetching tools, though it never names a sibling explicitly.

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?

"inside a known thread" implies the precondition that a thread_id is already in hand, and the second sentence steers agents away from body tools unless full content is needed. However, "message body tools" is not mapped to any concrete sibling name (e.g., mailbox_list_body, mailbox_get_message), so the routing guidance stays generic.

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