Update Inbox

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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the mutation/safety profile is covered. The description adds genuinely useful behavioral context — the email address is immutable and the update is partial (either field or both) — but says nothing about permissions, reversibility, or what happens to the untouched field.

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 the operation and its scope, then the constraint, then the immutability caveat. No filler or repetition of the schema text.

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 simple partial-update tool with full annotation coverage, complete parameter documentation, and no output schema, the description covers the operation, the valid inputs, and the key limitation. Only auth/permission expectations and the return shape are unaddressed, which are minor for this operation.

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 per-field descriptions already explain name (internal) vs fromName (display name), so the baseline is 3. The description earns an extra point by stating the cross-parameter constraint that at least one of name/fromName must be supplied — a rule the schema itself does not express.

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 ('Update an inbox in Resend') and immediately enumerates the two mutable attributes, which cleanly separates it from the many update-* siblings (update-inbox-thread, update-inbox-label, update-inbox-agent) that operate on different sub-resources.

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 precondition ('At least one of the two is required') and an explicit exclusion ('An inbox's email address cannot be changed'), which steers the agent away from an impossible call. It does not, however, discuss when to prefer this over related tools such as remove-inbox or update-inbox-agent.

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