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

Annotations already cover readOnly, idempotent, openWorld, and non-destructive. The description adds that the call is free, requires no wallet/payment, and takes no arguments, which is useful cost and auth context beyond the annotations.

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 front-loaded and compact: one sentence plus a short follow-up. Every clause (free, sample, purpose, cost, no wallet/payment/args) earns its place.

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 no-param preview tool with rich annotations and no output schema, the description fully explains cost and usage. The sample response itself will reveal the output shape, so nothing critical is missing.

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?

Zero parameters, so the baseline is 4. The description adds 'no arguments needed,' which aligns with the empty schema but is not strictly necessary.

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 states this is a free sample response for email_validate, letting the agent see the output shape before paying. It names the sibling email_validate and distinguishes the preview from the paid tool, so an agent can tell them apart without opening either 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?

It clearly positions the tool as a pre-purchase preview ('so you can see the shape before paying 0.006 USDC') and notes that no arguments are needed. It implies email_validate should be used for real validation but does not explicitly state the exclusion.

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