How to run a local MCP server in typeScript with node 23 without a build step

Yves Jutard — Fri, 30 May 2025 02:42:10 +0000

I experimented with writing and running a local MCP server in TypeScript and I ran into difficulties having it properly called from Claude.

In this article, I'll share the working config and the issues I encountered.

Prerequisite: MCP server code

I copy/pasted the TypeScript example from Claude documentation.

Goal: Direct Local execution

Claude rightfully recommends using TypeScript and suggests a build step to convert .ts to .js. However node >23.6 now supports direct execution of TypeScript with type stripping, so the build step felt unnecessary ❌.

TL:DR; Here is the working config:

Final, working, Claude's local config.json:

{
  "mcpServers": {
    "hello-world": {
      "command": "/Users/sam/.nvm/nvm-exec",
      "env": {
        "NODE_VERSION": "23"
      },
      "args": [
        "node",
        "--disable-warning=ExperimentalWarning --experimental-strip-types",
        "/Users/sam/work/src/mcp/module/src/index.ts"
      ]
    }
  }
}

Issues encountered and solutions

Everything path must be absolute

Claude's config doesn't perform any path interpolation or env inheritance, so everything has to be explicitly declared and all paths have to be absolute. No ~ or $HOME or PATH preset:

"command": "/Users/sam/.nvm/nvm-exec"
"/Users/sam/work/src/mcp/module/src/index.ts"

Calling the right node

I'm using nvm to manage my node runtimes. Even after installing the latest node 23 with nvm install 23, calling node from Claude yielded another version. The solution is to use nvm-exec with an env variable NODE_VERSION=23, see the config above. Note that nvm-exec must be referenced with an absolute path.

Stdout pollution

Since node 23's --experimental-strip-types is considered experimental, there is a warning message displayed on invocation. Since the local MCP protocol relies on stdin/stdout, this warning message disrupted the protocol.

The solution is to silence this warning with --disable-warning=ExperimentalWarning

Conclusion

It works!

I hope you'll overcome those issues faster thanks to this post. Good luck experimenting with MCP! Comments and reactions are appreciated 😊

Install those 6 browsers now… (Yes you need them all!)

Yves Jutard — Thu, 20 Mar 2025 05:25:37 +0000

I'm Frontend Software Engineer. I routinely use 2x browsers at once. Since last year, I further improved my productivity thanks to 2x extra browsers.

Disclaimer: 2 of them are macOs only.

1st: Main browser: Firefox

Firefox is not the greatest and fastest browser, but it has 2x killer features:

Vertical tabs: (webextension) THE killer feature. A collapsible tree of tabs is a huge productivity gain! Chrome absolutely rejects vertical tabs for no clear reasons.
Ad blocking: while Chrome is trying to kill ad blockers, Firefox promised they would keep them working. I use an advanced one called uMatrix but I heard good things about uBlock Origin.

2nd: Secondary browser: Chrome

The most supported browser, also the most "enterprise ready", the only one supporting all my company's internal tools.

Killer feature:

The standard: like it or not, all websites work on Chrome, especially business webapps.
Multi-profiles: allowing to seamlessly keep a separate personal profile on the side of a work one.

Be sure to tweak the security settings to block 3rd party cookies!

3rd: Dev browser: Chrome Dev

Using a dedicated Dev browser is a big gain! To properly debug websites (esp. perf issues), one needs:

no webextensions: daily-life webextensions such as password managers inject code into pages, add extra iframes etc. This is confusing when trying to debug a page, seeing extra logs & errors, extra classes on elements, confusing flamegraphs...
a cleanable browser: a dedicated dev browser allows you to safely "reset" your browser, clearing all cookies and site data without impacting all your work sessions on the main browser(s).
a defaulted browser: unlike your main browser which is likely "strenghtened" (strict Safe Browsing, 3p blocking…), you can keep the dev browser "defaulted" to experience it like most of your users do.

Chrome Dev is an excellent choice. It's evergreen and the most used browser anyway.

4th: "picker" browser: Velja

Velja by Sindre Sorhus is not a real browser but a browser picker. By setting it as the default system browser, it shows a picker upon click on a link from outside of a browser (ex. in your Terminal, Slack, Zoom…):

(Bonus) 5th: Mobile debugging browser Safari Technology Preview

Killer feature: mobile debugging. Safari Technology Preview can open dev tools on a connected iPhone, either a physical one or an emulated one. This is invaluable when fixing mobile issues.

I'm not doing much mobile debugging at the moment, but when needed, it's a must-have.

(Bonus) 6th: Responsive Development browser Polypane or Responsively

Killer feature: responsive development. Both browsers allow to simultaneously open several synchronised tabs with different viewport sizes.

Polypane is paid but feature-packed by very motivated devs

brew install --cask polypane

Responsively is free but has less features

brew install --cask responsively

I'm not doing much responsive dev at the moment, but when needed, it's a must-have.

That's it!

DEV Community: Yves Jutard