open_tab

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

With no annotations, the description bears full responsibility for behavioral disclosure. It explicitly discloses non-obvious behavior: the tab opens in the background and does not change focus. This adds significant value beyond the schema and is sufficient for a simple browser action, though it omits potential error cases or permissions.

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, each earning its place. The first states the core action and target, the second clarifies the key behavioral nuance. No filler or redundancy. Perfectly front-loaded and 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?

For a tool with one parameter, no output schema, and modest complexity, the description covers the essential purpose and behavior. The background-opening detail is crucial for user expectations. The sibling group includes navigation and focus tools, so the 'new tab' wording provides adequate context. Nothing critical 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?

Schema description coverage is 100% (url has 'URL to open'), so the baseline is 3. The description's reference to 'specified URL' adds no additional meaning beyond the schema. No format, validation, or edge-case information is provided, so it stays at the baseline.

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 uses a specific verb+resource: 'Open a new tab with the specified URL.' This clearly distinguishes it from siblings like close_tab, focus_tab, and navigate, as it explicitly denotes creating a new tab rather than modifying an existing one or navigating the current tab.

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 clear context by stating it 'Always opens in background (no focus change),' which implicitly tells when to use this tool instead of focus_tab or navigate. It lacks an explicit 'use this when' statement but conveys the practical scenario clearly, earning a 4.

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