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

With no annotations provided, the description carries the full burden of behavioral disclosure. It mentions features like attachments and scheduling but lacks critical details: it doesn't specify authentication requirements (e.g., API keys), error handling, rate limits, or what happens on success/failure. For a tool that sends emails, this is a significant gap in transparency.

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?

The description is concise and well-structured in two sentences, with no wasted words. It front-loads the core purpose and efficiently lists key features. However, it could be slightly more informative without losing conciseness, such as by hinting at behavioral aspects.

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?

Given the complexity of an email-sending tool with 7 parameters, no annotations, and no output schema, the description is incomplete. It lacks essential context like authentication needs, error handling, rate limits, and response format. This makes it inadequate for an agent to use the tool reliably in varied scenarios.

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?

The description adds minimal semantic value beyond the input schema, which has 100% coverage. It mentions 'plain text content, attachments and optional scheduling' and 'custom sender and reply-to addresses,' but these are already covered in the schema descriptions. No additional syntax or constraints are provided, so it meets the baseline for high schema coverage.

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?

The description clearly states the tool's purpose: 'Sends an email using the Resend API.' It specifies the action (send) and resource (email), and mentions key capabilities like plain text content, attachments, and scheduling. However, without sibling tools, there's no need for differentiation, so it doesn't score a 5.

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?

The description provides no guidance on when to use this tool versus alternatives. It lists features but doesn't specify scenarios, prerequisites, or exclusions. For example, it doesn't mention when scheduling might fail or if there are rate limits, leaving the agent with minimal usage context.

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