Look up contacts by email

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

Annotations already declare readOnly/idempotent/non-destructive, and the description partly restates this ('Reads only; nothing is created'). It adds value beyond annotations by disclosing the batch cap, and critically the return semantics — matching contacts plus which addresses had no match — which is otherwise unavailable since there is 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?

Four bolded, front-loaded sections (Purpose / Not for / Returns / Use when) with no filler. Each sentence carries distinct information: scope, exclusion, return shape, and usage trigger.

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 read tool, all an agent needs is covered: what it does, when to use it, the sibling to avoid, and what comes back (including unmatched addresses). With no output schema, the explicit Returns section fills the one real 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?

Schema coverage is 100% for the single 'emails' array parameter, so the schema already documents type and the 500-item limit. The description's 'up to 500 emails' adds no syntax beyond what is already structured; 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 (resolve) and resource (email addresses to contacts), including the batch scope of up to 500. It explicitly contrasts with plunk_list_contacts, so an agent can distinguish it from the many sibling contact tools without opening a 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 explicit 'Not for' (partial-address browsing → plunk_list_contacts) and 'Use when' guidance ('you hold a list of addresses and need their ids or subscription states'), plus a rationale against the one-lookup-per-address alternative. Both the selection condition and the exclusion are named.

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