open_tab

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

Beyond the annotations, the description discloses that each tab maintains independent cookies, storage, and login state, that the new tab becomes active, and that there is a maximum of 5 simultaneous tabs. It also explains the cookie injection behavior for pre-authenticated sessions. These details add significant transparency without contradicting the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false).

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, starting with a clear summary sentence, followed by key behavioral notes, then a bulleted parameter list. Each sentence adds useful information—no fluff—making it appropriately concise for a tool with three parameters.

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 presence of an output schema and annotations, the description covers the essential operational aspects: purpose, parameter semantics, side effects (active tab), and constraints (max 5 tabs). The only minor gap is what happens when the maximum is exceeded, but this is not required for a complete description.

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 input schema has no descriptions (0% coverage), so the description fully compensates. It details each parameter: 'name' is a unique identifier with alphanumeric+underscore and max 30 chars; 'url' is restricted to http/https; 'cookies' are pre-authenticated session cookies injected before navigation. This provides essential semantic meaning beyond the bare schema.

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 'Open a new browser tab with an independent session', identifying the verb (open), resource (browser tab), and key characteristic (independent session). It also distinguishes from sibling tools like switch_tab and list_tabs by emphasizing it creates a new tab. The addition of becoming the active tab and max 5 tabs further clarifies the tool's role.

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 context on when to use this tool by explaining each tab has its own cookies, storage, and login state, implying use when an isolated session is needed. However, it does not explicitly mention alternatives or cases where this tool should not be used, such as switching to an existing tab, which is handled by switch_tab. This earns a 4 rather than a 5 due to lack of explicit exclusions.

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