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 reveals the cost ($0.002 USDC) and the nature of the checks, which is useful. However, it does not state whether the operation is read-only, whether external data is sent, or what the response format looks like. The cost disclosure is a strong point, but the lack of side-effect or response details leaves a moderate gap.

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?

Two sentences with zero fluff. The first sentence front-loads the action and outputs, the second gives the use case and cost. Every word earns its place, and the structure is easy to scan.

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 single-parameter tool with no output schema, the description covers the essential context: what it does, what it returns, when to use it, and what it costs. It lacks explicit error-handling or edge-case information, but the tool is simple enough that this is a minor omission rather than a critical gap.

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 schema already documents the single parameter 'domain' as 'Domain or full email address' with 100% coverage. The description mirrors this by saying 'email address or domain' but adds no new semantic detail about format, normalization, or edge cases. Baseline 3 is appropriate since the schema does the heavy lifting.

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 opens with a specific verb ('Check') and clearly defines the resource ('email address or domain'). It enumerates the exact outputs (MX records, mail provider, SPF, DMARC, disposable-domain flag, deliverability score), making the tool's function unambiguous and distinct from the sibling tools, which target tech stacks, webpages, and pricing.

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 phrase 'Validate leads before sending' explicitly states the primary use case. It does not mention when not to use the tool or alternative tools, but the siblings are sufficiently different that no exclusion is necessary. The guidance is clear and actionable.

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