Create Inbox

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

Annotations only declare the safety profile (readOnly=false, destructive=false, openWorld=false); the description goes much further by disclosing the receive-verification prerequisite, the alternate forwarding mode that yields a receiving address, and two concrete failure codes (403 at plan inbox limit, 451 for blocked account). That is exactly the behavioral context an agent cannot get from structured fields.

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 sentences, front-loaded with the action, then purpose, prerequisites and error behavior in descending order of importance. No filler, no restating of the title.

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 noting that Resend returns a receiving address when forwarding is used, and it covers prerequisites and failure modes for a mutation tool. Combined with annotations covering the write/safety profile and a fully documented schema, an agent has everything needed to call this 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 name, fromName, forwarding and emailAddress are already fully documented, including the forwarding default and fromName character restrictions. The description only adds the 'verified for receiving' nuance on the address, which is marginal, so the baseline 3 applies.

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?

Opens with a specific verb+resource ('Create an inbox in Resend') and then defines what an inbox is ('receives email at an address on one of your domains and groups what arrives into threads'), which conceptually separates it from sibling resources like contacts, domains and broadcasts. An agent can tell this is the creation entry point for the inbox subsystem without opening the 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?

Gives a clear prerequisite ('The domain must already be verified for receiving, or set forwarding to true') and explains the forwarding path as a conditional alternative. It stops short of naming sibling tools or explicit when-not-to-use cases, so it is clear context rather than full routing guidance.

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