Run custom JavaScript in the active browser page to handle advanced RNW interactions, inspect state, or debug automation flows. Use when standard clicks and screenshots are not enough.
Execute JavaScript in the browser context. Useful for advanced interactions or debugging.
| Name | Required | Description | Default |
|---|---|---|---|
| script | Yes | JavaScript code to execute |
Changes observed during successful MCP inspections.
v2.0.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full disclosure burden for an arbitrary-code-execution tool. It says nothing about whether the script runs in page or isolated context, whether promises/async are awaited, what value is returned, or how errors surface — all critical for an eval tool. 'Execute JavaScript' restates the mechanics without behavioral context.
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?
Two short sentences with the core action front-loaded and zero filler. It is terse rather than padded, though the second sentence is vague enough that its value is marginal.
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?
For a code-execution tool with no annotations and no output schema, the description should at minimum explain return-value handling, since the schema cannot. Nothing about return values, async behavior, or failure modes is covered, leaving the agent unable to predict results of a call.
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?
Only one parameter and schema coverage is 100% ('JavaScript code to execute'), so the schema fully documents the input. The description adds no syntax, format, or wrapping guidance (e.g. whether the last expression is returned, whether it must be an expression vs. a statement). Baseline 3 applies.
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?
States a specific verb and resource: 'Execute JavaScript in the browser context.' This is clearly distinct from the action-specific siblings (rnw_click, rnw_type, rnw_scroll), which it implicitly positions as the alternative for scripted vs. discrete actions. It stops short of explicitly naming when to prefer a dedicated sibling over raw JS.
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?
'Useful for advanced interactions or debugging' implies the usage context but names no alternatives and gives no exclusion rule, e.g. 'prefer rnw_click/rnw_type for standard interactions.' The agent must infer that this is a fallback/escape-hatch tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.