Playwright MCP

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

Annotations indicate readOnlyHint=true, destructiveHint=false, and openWorldHint=true, which already convey that this is a safe, non-destructive operation with potential for open-ended outcomes. The description adds minimal context by specifying 'by index', but doesn't elaborate on behavioral aspects like what happens if the index is invalid, whether it changes browser focus, or any side effects. No contradiction with annotations exists.

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 a single, efficient sentence with zero waste—'Select a tab by index'—front-loading the core action. It's appropriately sized for a simple tool, with every word contributing directly to understanding the purpose.

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 tool's low complexity (one parameter, simple operation), annotations covering safety (readOnly, non-destructive), and no output schema, the description is minimally adequate. However, it lacks context on prerequisites (e.g., needing browser_tab_list first) or error handling, leaving gaps for an agent to infer usage 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?

The input schema has 100% description coverage, with the 'index' parameter fully documented as 'The index of the tab to select'. The description 'Select a tab by index' adds no additional meaning beyond this schema, such as index format (e.g., zero-based) or constraints. Baseline 3 is appropriate given high schema coverage.

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 'Select a tab by index' clearly states the verb 'select' and resource 'tab', with the specific mechanism 'by index' distinguishing it from other tab-related tools like browser_tab_list or browser_tab_close. However, it doesn't explicitly differentiate from all sibling tools, as browser_tab_new also involves tabs but for creation rather than selection.

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 no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., needing an open browser or existing tabs), when not to use it (e.g., if no tabs exist), or refer to sibling tools like browser_tab_list for listing tabs first. Usage is implied but not explicitly stated.

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