Open a URL

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

With no annotations, the description must carry the full burden. It discloses the result behavior ('The result names the application that actually received the URL') and mentions error cases ('Errors when nothing handles the scheme or macOS refuses'). It does not discuss side effects like app foregrounding or permissions, but for a URL-opening tool this is reasonably transparent.

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, front-loaded with the primary action, and uses no filler. Every sentence adds value: the first states the core function and option, the second explains the result and errors while pointing to a sibling tool.

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 two simple parameters, full schema coverage, and no output schema, the description covers all necessary aspects: what it does, how to use it (including the optional parameter), what it returns, and error behavior. The pointer to hs_list_apps completes the workflow.

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% as both parameters already have detailed descriptions in the schema. The tool description adds a cross-reference to hs_list_apps for bundle ids, but otherwise repeats schema content. Per the rubric, baseline is 3 since schema covers parameters well.

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 verb and resource: 'Open a URL' with the option to specify a bundle id. It distinguishes from siblings like hs_launch_app (which opens apps without URLs) and hs_list_apps (which lists apps). The purpose is specific and unambiguous.

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 provides context for when to use it (open a URL by default handler or specific app) and gives an explicit alternative reference ('Use hs_list_apps to find bundle ids'). It also mentions error conditions. However, it does not explicitly state when NOT to use it (e.g., when launching an app directly without a URL), though the sibling scope makes this implicit.

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