browser_open_url

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

Annotations already indicate non-read-only, open-world, and non-idempotent behavior. The description adds valuable context beyond these by disclosing the authentication prerequisite and the underlying OS-specific commands, which could affect failure modes. It does not contradict annotations and enriches the behavioral picture, so a 4 is appropriate.

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 two sentences, both information-dense. The first sentence states the primary action and permission requirement; the second adds platform-specific commands. Every clause contributes to understanding the tool, and there is no repetitive or filler content.

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 simple parameter set (1 param), no output schema, and existing annotations, the description covers the essential operational aspects: action, permission prerequisite, and platform behavior. It could mention potential error handling or return status, but for a straightforward browser-opening tool, the context is sufficiently 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 description coverage is 100% and the only parameter, 'url', already has a thorough description including the https:// default assumption. The tool description adds no additional parameter semantics beyond referencing 'URL' in the action. With full schema coverage, the baseline of 3 applies.

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 clearly states the tool's action with a specific verb and resource: "Open a URL in the user's default browser as a new tab/window." This distinguishes it from siblings like web_fetch (which retrieves content) and open_file_at_path (which opens local files), leaving no ambiguity about its purpose.

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 provides explicit context for when to use the tool by noting the prerequisite: "Requires prior browser permission (grant_browser_access)." It also adds platform-specific implementation details (macOS `open` vs. webbrowser module), but does not explicitly contrast it with alternatives or state when not to use it. This is clear usage context without formal exclusions, fitting a 4.

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