Verify Emails

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

Annotations provide readOnlyHint: true, which is consistent with verification. The description adds significant behavioral context beyond annotations: credit cost (1.5 per email), output fields, catch-all domain implications, and explicit scope boundaries (no disclosure of verification methods, infrastructure, etc.). No contradiction.

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 moderately long with multiple paragraphs, but each section serves a distinct purpose: core function, critical usage directive, presentation guidance, and scope boundary. It is front-loaded with the most important information and uses headings (ALWAYS, SCOPE) for scanability. Could be slightly more concise, but structure is logical and effective.

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?

Despite having an output schema (unseen), the description explicitly lists return fields and adds critical operational context (credit cost, batch processing expectation, catch-all behavior, scope limitations). With sibling tools covering different domains, this description fully prepares an agent for correct invocation and result handling.

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 coverage is 100% with the 'emails' parameter already described as 'Email addresses to verify.' The description adds the maxItems=1000 and minItems=1 (already in schema) plus the usage instruction to pass all at once, which is non-parametric guidance. Since baseline is 3 for high schema coverage, the description adds marginal value but does not significantly enhance parameter understanding beyond what's in the schema.

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 verb ('Verify') and resource ('email addresses') with a specific scope ('up to 1000 per call') and lists exact return values (existence, disposable, catch-all, free provider, deliverability score). It distinguishes itself from siblings by focusing solely on verification, not details (get_verification_details) or credits (get_credit_balance).

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?

Provides explicit guidance: 'ALWAYS pass every email the user asked about in a SINGLE call' with reasoning about credit waste and fragmented results. Also specifies when to decline and redirect (scope paragraph), and instructs the agent to surface the 'catch_all_domain' field in results. This fully covers when and how to use the tool versus alternatives.

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