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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered; the description adds meaningful behavior beyond that by noting the response renders an interactive UI and enumerating the returned fields (status, language, target URL, type, tester/video counts). It doesn't mention permissions or payload size, keeping it below 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?

Front-loaded with the action and resource, then the domain definition, then the return summary and the routing hint. The definition of a Userbrain test is a little longer than strictly necessary, but it earns its place by disambiguating the resource.

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-param, read-only fetch with an output schema already present, the description covers purpose, the prerequisite call, and even previews return fields. Nothing an agent needs in order to invoke it correctly is missing.

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% and the single testId parameter is fully documented in-schema, including its provenance from list_tests. The description reinforces that provenance but adds no format or type detail beyond the schema, so the 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 and resource ('Show the details of one Userbrain test by its id') and goes further to define what a test is (unmoderated study with target URL, language, tasks, videos), which lets an agent distinguish it from aggregate or listing siblings.

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?

Explicitly names the prerequisite/alternative ('Use list_tests first to find the testId'), which is the key routing instruction for this tool. It doesn't mention when to prefer get_insights, get_tasks, or get_videos, so it isn't a full when/when-not treatment.

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