open_url

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

With no annotations, the description carries the full burden of behavioral disclosure. It states the main action (opening URL in default browser) but does not disclose details such as whether it returns success/failure, whether it blocks, or what happens on invalid URLs. For a simple side-effecting tool, this is adequate but not rich.

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?

The description is a single, front-loaded sentence with zero filler. Every word contributes to understanding the tool's purpose, making it appropriately concise.

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?

Given the tool's simplicity (one parameter, no output schema, no annotations), the description sufficiently covers the essential context: what the tool does and what it acts on. It could mention error behavior or return value, but these are not necessary for basic usage, making the description complete enough.

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?

The input schema has 100% description coverage with 'URL to open' for the single parameter, so the schema already fully documents the parameter. The tool description adds no additional semantic value beyond the schema, hence the baseline score of 3.

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 'Opens a URL in the default browser' uses a specific verb ('opens') and resource ('URL'), clearly stating the tool's function. It is distinct from all sibling tools, none of which perform URL opening, so it differentiates itself effectively.

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?

The description clearly implies when to use this tool (whenever a URL needs to be opened), and there is no alternative among siblings that would require explicit exclusions. No prerequisites or conditions are mentioned, but the tool is simple enough that the context is self-evident.

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