Create Inbox Label

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

Annotations already declare this is a non-destructive mutation, so the bar is lower; the description adds real context beyond them by stating that creation has no side effect on threads, that names are unique per inbox ignoring case, and that an inbox caps at 100 labels. These constraints imply failure conditions the agent should anticipate, though error behavior itself is not spelled out.

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?

Four short sentences, front-loaded with purpose, then the non-effect caveat, then the follow-up tool, then constraints. Every sentence carries information the agent needs and none is redundant.

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?

For a mutation with no output schema, the description usefully references 'the ID this returns' and covers uniqueness and volume limits. It stops short of describing duplicate-name or limit-exceeded failure behavior, but the stated constraints give the agent enough to call it 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%, so all three parameters are already documented, including the hex color format and the inboxId/email-address option. The description's note that Resend picks a color when omitted largely repeats the schema's own wording, so it adds little beyond the 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 (create a label in a Resend inbox) and defines what a label is, distinguishing it from siblings like add-inbox-thread-labels, update-inbox-label, and list-inbox-labels. The agent can tell exactly what this tool produces without opening a 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 that creating does not apply the label and routes the agent to add-inbox-thread-labels to do so, which is strong when-to-use guidance. It does not explicitly contrast with update-inbox-label or list-inbox-labels, but the create-vs-apply distinction is the key ambiguity and it is resolved.

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