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

With no annotations, the description carries the full burden and does meaningful work: it discloses the verified-sender prerequisite and the text_content/html_content either-or requirement, neither of which is encoded in the schema. It omits rate limits, error behavior, and whether sends are live, so it is solid but not complete.

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?

Front-loaded with the one-line purpose, then a tight Args block where every line carries unique parameter meaning. No filler, no repetition of the name or obvious facts.

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?

An output schema exists, so the brief returns line is sufficient and the description needn't explain response structure. Parameter coverage is complete; only failure modes and delivery guarantees are absent, which are minor for a straightforward send tool.

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 description coverage is 0%, so the description must compensate, and it documents all five parameters with their meaning and role. It goes further by stating the conditional dependency between text_content and html_content, which the schema's nullable defaults do 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 (send) and resource (email) plus the delivery mechanism (Resend API) in the first line, which is enough for an agent to identify the tool unambiguously. There are no siblings to differentiate from, so nothing further is required.

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?

Usage is implied by the tool's obvious purpose, and the description adds one real prerequisite ('sender_email must be verified in Resend'), but it never states when to prefer this tool, what happens on failure, or any exclusions. Adequate but with clear gaps.

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