Create Inbox Label

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

Annotations already establish this is a non-destructive write (readOnlyHint=false, destructiveHint=false), so the bar is lower. The description adds genuinely useful behavior beyond them: no side effect on threads, case-insensitive name uniqueness per inbox, and a hard 100-label ceiling. It omits error/conflict behavior when the uniqueness or limit is violated.

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?

Five short sentences, no filler. The core action and the critical 'it does not apply the label' caveat are front-loaded immediately after the definition, before the routing hint and constraints.

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?

There is no output schema, so the description correctly compensates by telling the agent the call returns an ID and how to use it. Combined with the annotations' safety profile and the full schema coverage, nothing an agent needs to invoke this correctly is missing.

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 and the schema already documents name, color, and inboxId. The description adds meaning the schema does not: the uniqueness constraint and 100-label cap that govern the name parameter, plus confirmation that omitting color defers to Resend's pick.

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 (create) and resource (label in a Resend inbox), then defines what a label actually is ('a tag the threads in that inbox can carry'). An agent can distinguish this from list-inbox-labels, update-inbox-label, and remove-inbox-label 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?

Explicitly clarifies the post-creation flow: 'Creating one does not put it on anything: pass the ID this returns to update-inbox-thread to apply it to a thread.' This routes the agent to the correct sibling for the follow-up action. It stops short of stating when-not-to-use (e.g., versus update-inbox-label), so it is clear context without full exclusions.

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