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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds real context beyond them: the underlying Actor (skilled_glee/email-verifier), that it runs on the caller's own Apify account, and pay-per-event pricing at $0.001/email billed by Apify. It also discloses the return shape (pass/risky/fail plus reason codes) despite having no output schema.

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 dense sentences, front-loaded with the core action and its checks, then the execution/cost model. Every clause carries information an agent needs; nothing is repeated from the annotations or schema.

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 two-param batch verification tool with no output schema, the description covers what is checked, what the verdict looks like, cost, billing party, and which account executes it — everything needed to call it correctly and safely.

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 100%, with both params documented in-schema including the max-100 batch limit and the token fallback for clients that cannot send auth headers. The description adds no parameter-level detail beyond that, so the baseline 3 applies.

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+resource ('Check email addresses without sending mail') and enumerates exactly what is checked: syntax, MX, null MX, disposable domains, role accounts, free providers, typos, plus the pass/risky/fail verdict and reason codes. That resource is unmistakably distinct from the sibling extract_*/probe_urls tools, so an agent can route on it without opening the 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?

Usage context is clear (verifying a list of email addresses) and the boundary 'without sending mail' rules out a plausible misreading. However, no explicit when-to-use vs. alternatives or exclusions are given — though no sibling competes for this task, so the omission is low-cost.

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