Open tab(s)

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

With no annotations, the description carries the burden and reveals key behaviors: defaults to the first window, returns new tab ids (or pane ids in pane mode), and clarifies that each group becomes one tab. It could go further on permissions or error conditions, but the core effects are transparent.

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 dense but efficient, front-loading the core purpose and then adding mode-specific details in a structured way. It's slightly long, but every clause adds meaningful guidance—no fluff.

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 complex tool with nested objects, enums, and two modes, the description covers the essential invocation decisions: window default, group-to-tab mapping, the 'as' behavior, and return types. It doesn't cover every schema field or potential errors, but the schema fills those gaps, making this sufficiently complete for an agent to select and invoke 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?

Though schema coverage is 0%, the description compensates by explaining the meaning of 'as' (merging vs. tab creation), the grouping semantics ('Each group is one tab'), and the concept of a default window. It names several nested pane fields in the shorthand, but omits some (e.g., fontSize, sizes) and the exact windowId parameter name, so a 4 is appropriate.

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 the action: 'Attach one or more new tabs to an existing window' with fresh shells. It explicitly differentiates from the sibling tool open_pane by saying 'Use this (not open_pane) to add a whole tab, or several tabs, in one call.'

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?

Explicit usage guidance is provided: 'Use this (not open_pane) to add a whole tab, or several tabs, in one call.' It also explains an alternative mode 'Pass as:"panes"' for merging panes into the active tab, giving clear conditional direction.

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