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

Discloses key behaviors: default focus, background opening with active:false. No annotations exist, so description fully carries the burden. No contradictions. Lacks only minor details like default URL behavior, but sufficient for safe use.

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 efficient sentences: first states primary function, second provides usage guidance and sibling differentiation. No wasted words; front-loaded with key info.

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 simplicity (2 optional params, no output schema), description covers essential use cases and guidance. Minor missing details like error handling or return value are acceptable for this type of tool.

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 has 0% description coverage; description must compensate. It explains url as optional ('at a URL') and active with its effect (background). Could improve by specifying URL format or behavior when omitted, but overall adds needed meaning.

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?

Description clearly states action: 'Open a NEW tab (optionally at a URL) and focus it.' Differentiates from sibling 'navigate' by contrasting behaviors, making purpose 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?

Explicitly says when to use this over navigate: 'prefer this over navigate when the user says open/go to a site', and explains navigate replaces current tab. Also provides context for active:false in parallel batches.

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