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

Annotations already cover read-only/destructive/open-world safety, so the description's added value is the 'double-click' behavior: it launches an external GUI application on the user's machine rather than returning data. That is meaningful context beyond the structured hints, though it says nothing about what happens if the path is invalid or which machine the app opens on.

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, zero filler, with the core action and the mechanism in the first clause and the use case second. Nothing to trim and nothing buried.

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 two-parameter tool with rich annotations, full schema coverage and no output schema, the description covers the essential behavior. The only missing piece is guidance on the multi-device case, which the schema partially covers on its own.

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 the schema already defines the required absolute path / http(s) URL and the optional device. The description's examples (images, PDFs, URLs) loosely reinforce the accepted path forms but add no syntax or format detail, and it never mentions the device parameter.

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 ('Open a file or URL') and disambiguates the mechanism with 'with the default application on the computer (like double-clicking it)'. That analogy separates it from read_file or run_command without naming those siblings explicitly.

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?

'Use for images, PDFs, URLs or any file you want the user to see' gives a clear positive-use condition. It stops short of exclusions — nothing tells the agent not to use this when it actually needs file contents (read_file) or to launch a program (run_command/start_process).

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