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microsoft

Playwright MCP Server

Official
by microsoft

browser_run_code_unsafe

Destructive

Run arbitrary JavaScript in the Playwright server to automate browser interactions. Warning: this tool executes code with full server access, equivalent to remote code execution.

Instructions

Run a Playwright code snippet. Unsafe: executes arbitrary JavaScript in the Playwright server process and is RCE-equivalent.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
codeNoA JavaScript function containing Playwright code to execute. It will be invoked with a single argument, page, which you can use for any page interaction. For example: `async (page) => { await page.getByRole('button', { name: 'Submit' }).click(); return await page.title(); }`
filenameNoLoad code from the specified file. If both code and filename are provided, code will be ignored.
Behavior3/5

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

Annotations already provide destructiveHint=true and openWorldHint=true. The description reinforces this by labeling it 'Unsafe' and 'RCE-equivalent', but does not add new behavioral details beyond what annotations convey. It is consistent with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, front-loaded sentence that immediately states the action and critical warning. No words are wasted; every part earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's power and lack of output schema, the description could mention return values or error handling. However, for a code runner, the return is implicit in the code. The warning is sufficient, but completeness is adequate.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, with parameters well-described in the schema itself (including a full example for 'code'). The tool description adds no extra parameter semantics beyond the schema, so baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the verb 'Run' and the resource 'Playwright code snippet'. The warning about unsafety and RCE-equivalency differentiates it from sibling tools like browser_evaluate, making its purpose distinct and specific.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies through its warning that this tool is for advanced use cases requiring server-side code execution, but it does not explicitly state when to use it versus alternatives like browser_evaluate. No exclusions or when-not guidance is provided.

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

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