open_tab

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

Since no annotations are provided, the description fully discloses behavior: it mentions side effects (creates a tab, registers ID, stays open until close_tab), lazy instance launch, and the exact return structure (tab_id, target_id, url, label). This goes beyond the schema and gives the agent a complete mental model.

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 well-structured, front-loading the purpose and then detailing side effects, return values, usage, and alternatives. It is slightly verbose but every sentence contributes meaningful information without redundancy, earning a solid 4.

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 tool's complexity (3 optional params, no output schema, 30+ siblings), the description is complete: it covers what, why, when, side effects, return format, and differentiation from related tools. An agent has everything needed to call it correctly.

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 covers all parameters at 100%, but the description adds value: url defaults to 'about:blank', label must be unique, and instance_id derives from open_instance/list_instances with an 'omit for default' guidance. This enriches the agent's understanding beyond raw schema types.

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 function: 'Opens a new tab in the specified Chrome instance.' It names the specific resource (tab) and the action (open), and differentiates itself from siblings by explicitly mentioning 'navigate' and 'list_tabs' as alternatives with different purposes.

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 explicitly states when to use this tool: 'Use this to work with several pages in parallel while keeping their CDP state isolated per tab.' It also provides clear alternatives: 'navigate' for altering the active tab and 'list_tabs' for enumerating existing tabs, giving an agent precise routing guidance.

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