Split the window between two tabs

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

The readOnlyHint=false annotation already signals mutation; the description adds real value by disclosing the reversal path (browser_unsplit_view or closing a pane) and that this is a Firefox gBrowser feature. It does not cover failure conditions such as a pane already being split, but the added context is substantial.

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?

Three tight sentences, purpose first, parameter modes second, reversal last. No filler or restatement of the title.

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 output schema, the description should ideally hint at what comes back (context ids, pane handle) or what happens to the active tab after splitting. That is a minor gap against an otherwise complete picture of a 3-parameter mutation tool.

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 coverage is 100%, so the baseline is 3, but the description adds the combination logic the schema doesn't spell out: either pass two contexts, or one context plus a url for the second pane, and the default first tab is the active tab. That mutual-exclusivity guidance is the useful extra.

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 ('Put two tabs side by side in one window') plus the underlying API, and explicitly distinguishes itself from browser_unsplit_view. An agent can immediately tell this is the split operation and not a general tab-move.

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?

Gives a concrete use case ('watching one page while the agent works on another') and names the reverse operation and the alternative reversal (closing one of the two tabs). It stops short of stating when-not to use it, e.g. cross-window or non-Firefox constraints, so it falls just short of a 5.

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