List Inbox Labels

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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so safety is covered. The description adds genuinely new context: the exact return fields, that the output is ID-bearing and feeds other tools, and that inbox IDs come from list-inboxes. It omits pagination/rate-limit behavior, so it falls just short of 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?

Front-loaded with Purpose, then NOT for, Returns, and When to use – a scannable structure where each block earns its place. Slightly heavier than necessary for a one-parameter list tool, keeping it from a 5.

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?

With no output schema, the description correctly enumerates the return fields (id, name, color, created_at) and explains the upstream dependency on list-inboxes and downstream consumers of the IDs. An agent has everything needed to invoke and use the result.

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% for the single inboxId parameter, so the baseline is 3. The description adds meaning beyond the schema by telling the agent where to source the value ('Get the inbox ID from list-inboxes'), which the bare 'Inbox ID' schema description does not.

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 labels in one Resend inbox'), and parenthetically clarifies what a label is ('the tags its threads can carry') plus the return grain ('each with its ID'). It also distinguishes itself from the closely-named siblings update-inbox-thread, list-inbox-threads, and create/update/remove-inbox-label.

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 the two sibling tools that consume label IDs (update-inbox-thread, list-inbox-threads) and the 'When to use' block states the triggering conditions, including the optimization of reusing IDs already printed on threads. Nothing about when to call this versus alternatives is left to inference.

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