browser_close_tab

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

With no annotations provided, the description carries the full burden. It discloses two behavioral traits: the default action when no index is given and the fact that it returns the updated tab list. However, it omits important edge-case behaviors such as whether the index is zero-based, what happens on an invalid index, or whether closing the last tab terminates the browser. These gaps prevent a higher score.

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 two concise sentences. The first sentence states the core action and the parameter, the second sentence describes the return value. There is no redundant or filler language, and the front-loading is effective.

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 simple one-optional-parameter tool, the description covers the main behavior and return value, which is helpful since there is no output schema. However, it leaves out practical details such as indexing convention (zero-based vs one-based) and error handling for out-of-range indices. These are relevant in a browser automation context, making the description not fully complete.

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 provides only a property name 'index' with a type number and zero documentation. The description adds key meaning: the index identifies which tab to close, and omitting it means the active tab is closed. This explains the parameter's role and optionality, going well 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 starts with a specific verb and resource: 'Close a tab by index'. It clearly distinguishes this tool from siblings like browser_tabs, browser_switch_tab, and browser_navigate by focusing on the closing action. It also clarifies the default behavior when no index is given, which further sharpens the purpose.

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: use this tool to close a tab, optionally specifying an index. It also explains the behavior when no index is provided ('or the active tab'), which is practical usage guidance. It doesn't explicitly name alternatives or exclusions, but the purpose is so distinct from siblings that the context is clear without them.

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