Verify email address

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and openWorldHint, so the safety profile is covered. The description adds genuine behavioral context beyond that: the specific signals checked (syntax, disposable-domain lists, plus-addressing, MX records) and the fact that it does not consult the contact database. It stops short of noting rate limits, external-service dependency, or latency, so it is not a full 5.

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?

Four short, bold-labeled sections (Purpose / Not for / Returns / Use when) with the routing information front-loaded and zero filler sentences. The structure makes it scannable, and every line carries distinct information.

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?

There is no output schema, and the description compensates by describing the return value ('a verdict on the address with the reasons behind it'). Combined with annotations covering the safety profile and the explicit sibling routing, an agent has everything needed to call this correctly.

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?

Only one parameter and schema description coverage is 100% ('Email address to validate'), so the schema already carries the parameter semantics. The description adds no format guidance (e.g. trimming, multiple addresses, normalization) beyond what the schema states. Baseline 3 applies when 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?

States a specific verb (verify) and resource (email address) and enumerates exactly what 'verify' means here: syntax, disposable-domain lists, plus-addressing, and MX records. That level of specificity lets an agent distinguish it from contact-lookup tools 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?

Contains an explicit 'Not for' section naming the sibling alternatives (plunk_get_contact, plunk_lookup_contacts) and the condition that selects them ('checking whether someone is already a contact'). It also gives a positive trigger ('Use when: before adding an address a user typed, or when investigating bounces'), so both routing directions are covered.

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