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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely new context: the result is one row per list with specific fields, which matters because there is no output schema. It does not mention rate limits or pagination, so not a 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?

Two compact sentences, front-loaded with the purpose and result shape before the raw endpoint path. Little waste, though the trailing 'GET /Contact/ContactDetails' is of marginal value to an agent.

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 one-parameter read search, the description covers purpose, scope (all lists), and return shape, which is required since there is no output schema. The only real gap is whether the email must match exactly, which affects correct invocation.

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?

Single parameter with 100% schema coverage, so the schema already documents 'email' fully. The description adds no matching rules (exact match, case sensitivity, normalization) beyond what the schema states, so 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 (Find) and resource (an email address across all lists), plus the row-level output shape (list name, contact id, master-unsubscribe flag). This is enough to tell it apart from benchmark_get_contact and benchmark_list_contacts, though it never names a sibling explicitly.

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 is implied by 'Find an email address across all lists' – it's the lookup-by-email tool – but there is no explicit when-to-use versus benchmark_get_contact or benchmark_list_contacts, and no note on match semantics (exact vs. partial).

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