execute_js
Execute JavaScript code in an isolated environment
LABSCO SUMMARY
One tool, and the limits are arguments to it rather than server configuration.
execute_js takes memory and timeout alongside the code, so the ceiling belongs to the call and a client can run an untrusted snippet tighter than a trusted one without restarting anything. The set is exactly this one capability: no file access, no package installation and no session that persists between calls appear in the tool surface.
What it is
A single-tool execution server that evaluates JavaScript in an isolated environment under caller-set limits.
What you get
- Isolated execution of a code string: execute_js runs the JavaScript you pass and returns its result.
- Bounded runs: the same call takes a memory limit and a timeout, so a snippet that loops or allocates without end is stopped by the sandbox rather than by the host.
Requirements
Nothing beyond the host the server runs on — the tool takes no account, key or external service, only the code and its limits.
Setup effort
One command — npx -y js-sandbox-mcp-server
USE CASES
01
Finding out what a snippet returns before it goes near the codebase
Run the JavaScript in an isolated environment with a memory ceiling and a timeout set on the call itself, and read the result back.
1 tool
Counted once with only startup setup. Other versions, modes or optional credentials may expose a different list.
BEFORE YOU INSTALL
What to know first
Tools you get
1 tool when we connected.
Requires
npx on PATH
CONTEXT COST
Light Standing cost
Rated by the size of the one tool definition that rides along on every turn
INSTALLATION
Connect your client
Add the block to your client, or run the command directly.
Server setup
Configuration file
JSON
{
"mcpServers": {
"js-sandbox-mcp-server": {
"command": "npx",
"args": [
"-y",
"js-sandbox-mcp-server"
]
}
}
}npx
TERMINAL
npx -y js-sandbox-mcp-server
