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

Annotations already establish that this is a read-only, non-destructive, non-open-world operation, so the description's burden is lower. It adds useful behavioral context by noting the lookup is case-insensitive and returns the contact if it exists, though it does not discuss not-found handling or rate limits.

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?

Three short sentences with no wasted text. The primary lookup behavior is front-loaded, followed by return behavior and the sibling alternative.

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 simple one-parameter lookup with a full output schema and annotations covering safety, the description supplies everything an agent needs: lookup key, case sensitivity, return semantics, and an alternative for broader searches.

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?

The single email parameter is fully described in the schema, so the baseline would be 3. The description adds semantic value by specifying that matching is case-insensitive, which is not captured 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 states a specific verb and resource: 'Look up a CRM contact by email address.' It adds the unique lookup key and case-insensitive behavior, and names a sibling alternative for broader searches, so an agent can distinguish it from search_leads 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?

It clearly routes broader searches by name, company, stage, or phone to search_leads, which is an explicit alternative. However, it does not explicitly differentiate from get_contact or list_contacts, so the routing guidance is clear but not fully exhaustive.

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