The pitch is narrow and honest: one tool, one job — pull the real value of a variable out of a deployed app, which is exactly the thing traditional debugging cannot reach on a serverless deployment. Because it resolves line numbers through AST analysis rather than trusting the number you typed, a stale line reference degrades into the right variable rather than the wrong one.
The MCP server for return0, a service for debugging production Node.js applications in real time. It connects the editor to the running application, so a question about what a variable actually holds in production is answered from the live process rather than from logs or a local reproduction.
- The runtime value, type and timestamp of named variables pulled from a running production application, requested as a list of files each carrying the variable names and their line numbers — `variable_extractor`
- Line numbers corrected before the lookup: the server reads the source file and uses TypeScript AST analysis to locate the variable accurately even when the line has moved
A return0 API key in `RETURN0_API_KEY`; the documentation at getreturn0.com/docs covers how to obtain one, and `demo` works for testing. Node.js, since the server is launched with `npx -y @return-0/mcp-server`. The package is `@return-0/mcp-server` (1.0.2) and installs on first launch. It reads your source files from the local filesystem, so it expects to run on the machine holding the code.
One command plus a key — npx -y @return-0/mcp-server, then supply credentials