Open a new browser window

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

Annotations only supply readOnlyHint=false; the description adds real behavioral context beyond that: a new window is 'a visible change on screen' and leaves an artifact requiring cleanup. That is exactly the kind of side-effect disclosure a mutation tool needs. It stops short of noting focus/background behavior or whether the window persists across sessions, so not a full 5.

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 sentences plus a clarifying clause; the identity/return value is front-loaded and the sibling comparison follows immediately. No redundant restatement of the title or schema.

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 zero-required-param creation tool with no output schema, the description covers what it produces (context id), what it costs (visible change, cleanup), and the correct alternative. That is everything an agent needs to choose and call it.

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 description coverage is 100%, so both params (url, background) are already documented in the schema; the baseline is 3. The description adds no semantics about url defaults or what background=true means for focus, so it does not exceed the baseline.

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?

States a specific verb and resource ('Open a new browser window') and grounds it in the underlying primitive (BiDi browsingContext.create with type "window"), plus declares the return value (the context id). It explicitly frames a window as a top-level context, which distinguishes it from tab-level siblings.

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?

Names the alternative explicitly — 'Use browser_new_tab when you only need another tab' — and gives the condition that selects it. It also routes cleanup to browser_close_window, so the full lifecycle decision is covered.

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