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

Annotations already declare the safety profile (non-destructive, non-idempotent, not open-world), so the bar is lower. The description adds genuine context beyond them: the operation goes through the OS default handler and the path is validated against the paired computer policy, which tells the agent a rejection is possible for unpermitted paths.

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 sentences, no filler, and the usage trigger is front-loaded before the policy caveat. Every sentence earns its place.

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-parameter tool with an output schema (so return values need no explanation) and annotations covering the safety profile, the description is nearly complete: purpose, trigger, and the policy-check constraint. Only the absence of any alternative-tool guidance keeps it from a 5.

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 (path, device) are already documented in the schema, and the description adds no format or syntax detail beyond the schema. Baseline 3 applies when the schema does the heavy lifting.

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 gives a specific verb (open) and a precise resource (an existing permitted file or directory, via its configured default application), and the 'default application' mechanism implicitly separates it from siblings like launch_app (starts an app) or reveal_path (shows in file manager). It stops short of naming any sibling explicitly, so it stops at a strong 4.

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 states the trigger condition clearly ('when the user wants the desktop operating system to open'), which gives the agent a usable context for selection. It does not name an alternative tool or an explicit when-not condition, so no credit for routing guidance.

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