List Inbox Thread Emails

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

Annotations already cover the safety profile (readOnlyHint, destructiveHint=false, openWorld=false), so the bar is lower, and the description goes well beyond them: it discloses that bodies are omitted, the oldest-first ordering, the enumerated return fields, and the pagination protocol. It does not cover rate limits or error behavior, keeping it from a 5.

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?

Bold section headers front-load purpose, exclusions, returns, and usage, so scanning is fast. It is somewhat long, and the pagination sentence is dense, but nearly every clause carries distinct information.

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?

No output schema exists, yet the description enumerates the returned fields, so the agent knows what a call yields. Pagination direction, cursor reuse, and the ID's role in sibling tools are all covered for a 5-parameter 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 coverage is 100%, so the baseline is 3, but the description maps the API's cursor params to agent action ('pass the last email's ID back as "after" for the next, newer page; pass the first email's ID as "before" when paging backward'), which is meaningfully beyond the raw schema text. It also clarifies that a message's ID IS the emailId other tools accept, tying the parameter to cross-tool usage.

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?

States a specific verb and resource ('List the emails in one Resend inbox thread') plus two key qualifiers: 'oldest first' and 'without their bodies'. The contrast with get-inbox-thread-email and get-inbox-thread makes the scope unambiguous against siblings.

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?

An explicit 'NOT for' block names both alternatives and the conditions that select them (body reading vs folder/labels/read state). The 'When to use' section adds the remaining positive trigger: paging a long thread or listing just the emails.

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