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 the safety profile is covered. The description adds non-obvious context beyond that: the exact return fields, and the chaining guidance that thread tools already print label IDs so a fresh lookup may be unnecessary.

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 make it scannable and the purpose is front-loaded, with the exclusion rule immediately after. It is slightly longer than strictly necessary for a one-parameter read tool, but every section 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?

With no output schema, the description compensates by enumerating the returned fields (id, name, color, created_at). Combined with the ID-sourcing guidance and the sibling routing, an agent has everything needed to call and use this tool 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 coverage is 100% and the single parameter is documented in the schema itself, which sets the baseline at 3. The description adds sourcing guidance ('Get the inbox ID from list-inboxes'), which is meaningful for an opaque identifier, pushing it slightly above baseline.

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') plus the scope of what a label is ('the tags its threads can carry'). It explicitly distinguishes itself from add-inbox-thread-labels and list-inbox-threads, so an agent can route without opening any schema.

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?

Contains an explicit 'NOT for' block naming the two alternative tools and the inverse operations they perform, then a 'When to use' section describing the triggering user intent and the ID-reuse shortcut. When-to-use, when-not-to-use, and alternatives are all present.

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