MCP Accessibility Scanner

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

Annotations provide readOnlyHint=true, destructiveHint=false, and openWorldHint=true, indicating a safe, non-destructive operation with potential for unknown outcomes. The description adds minimal behavioral context beyond this—it specifies 'by index' but doesn't explain what happens if the index is invalid, if selection changes focus, or any side effects. It doesn't contradict annotations, but offers little extra insight into tool behavior.

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: 'Select a tab by index'. It's front-loaded with the core action and method, with zero wasted words. Every part earns its place, making it highly concise and well-structured for quick understanding.

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 (1 parameter, no output schema) and rich annotations (covering safety and world hints), the description is minimally adequate. It states what the tool does but lacks completeness in usage guidelines, error handling, or integration with siblings like browser_tab_list. For a simple selection tool, it meets basic needs but leaves gaps in operational context.

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 1 parameter with 100% description coverage ('The index of the tab to select'), so the schema fully documents the parameter. The description adds no additional meaning beyond what's in the schema—it repeats 'by index' without clarifying format (e.g., zero-based vs. one-based) or constraints. Baseline score of 3 is appropriate as the schema carries the burden.

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 action (select) and resource (tab), with the method specified (by index). It distinguishes from siblings like browser_tab_list (lists tabs) and browser_tab_close (closes tabs), though it doesn't explicitly contrast them. The purpose is specific but could be more distinctively positioned among similar tab operations.

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 direct alternatives like browser_tab_list for identifying indices. Usage is implied by the action but lacks explicit context for decision-making.

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