Register a JavaScript snippet that will run on future document loads before page scripts execute. Use this for preload hooks, environment patches, and early instrumentation.
AI agents invoke inject_preload_script to trigger actions in JS Reverse Strong MCP. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
The tool allows injection and execution of custom code in a privileged position (preload phase) within a browser environment. While not immediately destructive or financial, it enables arbitrary code execution whose effects depend on the injected script content.
From the tool's definition 'Register a JavaScript snippet that will run on future document loads before page scripts execute' — this directly executes arbitrary JavaScript code in the browser context with early access to the DOM and global scope before other page scripts run.
Documented attack patterns abuse exactly the kind of access inject_preload_script gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and JS Reverse Strong MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for inject_preload_script:
{
"version": "1",
"default": "deny",
"tools": {
"inject_preload_script": {
"limits": [
{
"counter": "inject_preload_script_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}inject_preload_script stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Register a JavaScript snippet that will run on future document loads before page scripts execute. Use this for preload hooks, environment patches, and early instrumentation. It is categorised as a Execute tool in the JS Reverse Strong MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the JS Reverse Strong MCP server in PolicyLayer and add a rule for inject_preload_script: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches JS Reverse Strong MCP. Nothing to install.
inject_preload_script is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the inject_preload_script rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for inject_preload_script. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
inject_preload_script is provided by the JS Reverse Strong MCP server (lwjjike/jsreverser-strong-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from JS Reverse Strong MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
85 JS Reverse Strong MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.