List open pages

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

Annotations already mark this as read-only and non-destructive, so the safety profile is covered. The description adds valuable behavioral context: indices shift dynamically and the default page target behavior (selected page or most recent tab). This goes beyond the structured annotations and helps the agent reason about state changes.

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 three sentences, each serving a distinct purpose: what it returns, the dynamic index warning, and the page-selection behavior. No wasted words; information density is high and well-organized.

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?

With no parameters, presence of an output schema, and strong annotations, the description fully covers the tool's behavior. It explains the output fields, index semantics, and interaction with other tools, making it complete for an agent to select and invoke the tool 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 tool has zero parameters, so there is no parameter burden on the description. The baseline for no parameters is 4, and the description appropriately omits param details since none exist. No unnecessary parameter information is needed.

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 'List' with a clear output scope: 'every open browser tab with its index, URL and title.' It distinguishes itself from sibling tools by focusing solely on tab enumeration, and even connects the index to select_page/close_page, making the purpose unmistakable.

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?

Provides clear usage context by explaining that indices are positional and shift, so the agent should re-read rather than reuse stale indices. It also clarifies how tools act on the selected page or the most recent tab. However, it does not explicitly compare against alternatives like get_page_content or take_snapshot, though the purpose makes the use case fairly obvious.

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