Open a URL in the default browser using the allowed schemes: http, https, and mailto.
Open a URL in the default browser. Only http, https and mailto are allowed; every other scheme is refused. For local files and folders use file_open instead.
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | URL to open. |
Changes observed during successful MCP inspections.
v1.1.3Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden. It discloses the key behavioral constraint (only http, https, mailto allowed; others refused) and the target (default browser). It doesn't mention error handling or side effects, but these are minor for this simple action.
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 with zero redundancy. The core action is front-loaded, followed by the restriction and the alternative. Every clause 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 one-parameter tool with no output schema and no annotations, the description fully equips an agent to invoke it correctly. It covers allowed inputs and routing to the right sibling. Nothing essential is missing.
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 schema already describes the parameter as 'URL to open' (100% coverage), giving a baseline of 3. The description adds the scheme restriction, which clarifies what values are valid, going beyond the schema's generic description.
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 action ('Open a URL in the default browser') with a specific verb and resource. It also differentiates from the sibling file_open by specifying allowed schemes and explicitly naming the alternative for local files/folders.
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 explicitly states when to use this tool (for http, https, mailto URLs) and when not to (for local files/folders, use file_open). This provides clear selection guidance among siblings with no ambiguity.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.