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

The readOnlyHint annotation already covers the safety profile. The description adds the GET endpoint and the runtime rule that at least one identifier must be supplied (a constraint the schema itself does not enforce, since neither param is required), which is genuinely useful. It doesn't disclose what happens when no match is found or the response shape.

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 short sentences, front-loaded with the verb, resource, and identifier rule; the endpoint reference is a compact trailing detail. Nothing is wasted.

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 two-param lookup the core is covered, but with no output schema the description should ideally state what a successful (and unsuccessful) lookup returns to make the tool fully self-contained. As written it leaves the return behavior implicit.

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 description coverage is 100%, so both parameters are already documented and the baseline is 3. The description reinforces the email/userId choice and the at-least-one rule but adds no format or syntax detail beyond 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?

States a specific verb ('Find') and resource ('a contact') plus the two lookup keys, which clearly separates it from the mutating siblings (create/update/delete) and list tools. It stops short of explicitly naming a sibling or specifying that it returns a single contact rather than a collection.

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?

'Supply at least one' of email or userId gives a usage constraint on the arguments, but there is no guidance on when to prefer this over loops_list_contact_properties or other lookups, nor prerequisites like API-key scope.

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