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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description's real contribution is the return-shape disclosure (summary vs. expanded version list vs. device names), which matters because there is no output schema; it stops short of stating result size, pagination or any limits on the expansion.

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 sentences, front-loaded with purpose, then return shape, then the expansion rules — no filler. The middle sentence is densely packed with parenthetical detail but every clause carries information an agent needs to predict output size.

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?

A read-only, no-required-parameter discovery tool with no output schema; the description compensates by describing what each call shape returns, which is the main thing an agent needs. Only the 'type' filter and the absence of any note on result size keep it from being fully complete.

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%, so baseline is 3, but the description goes beyond the schema by explaining the interactive effect of the parameters: os alone expands versions, os plus browser narrows further, and os=ios/android switches to device names. The 'type' parameter is not addressed in the description, leaving a small gap.

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 ('Lists the OS, browser and device combinations TestMu AI supports') and adds the intent ('to find valid os, browser and version values for a test configuration'), which is enough to tell it apart from most siblings. It does not, however, distinguish itself from the nearby listDevicesForTesting, which an agent could plausibly confuse with the device-listing mode described here.

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 mode-selection guidance: no filters returns a compact summary, os (+optional browser) returns the full version list, and os=ios/os=android returns device names. That is concrete when-to-use guidance for each calling pattern, though it offers no explicit exclusion pointing to a sibling tool.

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