Playwright MCP

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

Annotations provide readOnlyHint=false, openWorldHint=true, and destructiveHint=true, indicating this is a mutable, potentially destructive operation with open-world assumptions. The description adds minimal behavioral context beyond this—it mentions evaluating JavaScript but doesn't clarify what 'destructive' entails (e.g., modifying page state, triggering side effects) or any rate limits, permissions, or error handling. 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 extremely concise—a single, front-loaded sentence that directly states the tool's purpose without unnecessary words. Every part of the sentence ('Evaluate JavaScript expression on page or element') contributes essential information, making it efficient and well-structured.

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 complexity (JavaScript evaluation with potential side effects), destructive annotations, and lack of output schema, the description is insufficient. It doesn't explain return values, error conditions, security implications, or how it differs from siblings like browser_run_code. For a tool with open-world and destructive hints, more context is needed to guide safe and effective use.

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 description coverage is 100%, with clear parameter descriptions in the schema (e.g., function as JavaScript code, element as human-readable description, ref as exact target reference). The description adds no additional parameter semantics beyond what's in the schema, such as examples of valid expressions or interaction between parameters. 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 clearly states the verb ('Evaluate') and resource ('JavaScript expression on page or element'), making the purpose understandable. It distinguishes from some siblings like browser_click or browser_navigate by focusing on JavaScript execution, though it doesn't explicitly differentiate from browser_run_code which might have overlapping functionality.

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 like browser_run_code or other JavaScript-related tools. It mentions 'page or element' context but doesn't specify prerequisites, constraints, or typical use cases, leaving the agent to infer usage scenarios.

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