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 genuine behavioral context beyond that: the ordering rule (most recent activity first) and the meaning of video_count vs new_video_count, which an agent cannot derive from annotations.

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-loads purpose, then interpretation rules, then return shape — a sensible order. The final sentence enumerating returned fields partly duplicates the output schema, making it slightly longer than necessary.

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 zero-parameter read tool with an output schema and read-only annotations, everything an agent needs is present: what a test is, how results are ordered, how to resolve 'the last test', and what fields appear. No material gaps remain.

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?

Zero parameters, so there is no parameter semantics to explain; baseline 4 applies. The description correctly does not invent parameter details.

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 ('List the authenticated user's Userbrain tests') and then defines what a test actually is (unmoderated usability study with URL, language, tasks, tester videos). This domain grounding lets an agent distinguish list_tests from get_test/get_videos without opening any 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?

Gives clear interpretive guidance for ambiguous user phrasing: 'the last test' / 'the latest test' maps to the first item in this list, which is valuable routing context. It does not, however, explicitly name siblings like get_test for fetching a single test by id, leaving that inference to the agent.

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