MCP Accessibility Scanner

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

Annotations already indicate destructiveHint=true and readOnlyHint=false, so the agent knows this is a destructive write operation. The description adds no behavioral context beyond this, such as what happens if no tabs exist, whether it's reversible, or if it requires specific permissions. However, it doesn't contradict annotations, so it meets the baseline for having annotations.

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 extremely concise with just three words ('Close a tab'), which is front-loaded and wastes no space. Every word directly contributes to understanding the tool's purpose, making it efficient and easy to parse.

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 destructive nature (destructiveHint=true) and lack of output schema, the description is insufficient. It doesn't explain what happens after closing a tab (e.g., browser behavior, return values, or error conditions), leaving gaps that could confuse an agent in practical use. The annotations help but don't fully compensate for missing contextual details.

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 parameter 'index' fully documented in the schema itself. The description adds no additional meaning about parameters, such as explaining tab indexing conventions or edge cases. This aligns with the baseline score when schema coverage is high.

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 'Close a tab' clearly states the action (close) and resource (tab), making the purpose immediately understandable. It distinguishes from siblings like browser_tab_list (list tabs) and browser_tab_new (create tab), though it doesn't explicitly contrast with them. The description is specific but lacks explicit sibling differentiation, which keeps it from a perfect score.

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 tab), exclusions, or compare with related tools like browser_close (which might close the entire browser). Without such context, an agent might struggle to apply it correctly in complex scenarios.

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