cfmlFiddle - Compare ColdFusion, Lucee, and BoxLang Side-by-Side

Mike's Notes

Thank you, James. This will help with code testing.

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Last Updated

23/04/2026

cfmlFiddle - Compare ColdFusion, Lucee, and BoxLang Side-by-Side

By: James Moberg
myCFML: 16/04/2026

Mike is the inventor and architect of Pipi and the founder of Ajabbi.

I built a local CFML playground that runs 10 engines at once

I've been writing CFML for a long time. Long enough to remember when testing something meant editing a file, refreshing the browser, and hoping the server hadn't crashed. We have better tools now, but I kept running into the same problem: I'd want to check how something behaves on CF2021 vs CF2025, or whether Lucee handles a date function differently than Adobe, and there wasn't a good way to do that without maintaining a bunch of separate installs.

The online tools help. CFFiddle.org, TryCF.com, and Try BoxLang are all useful when you need a quick test. But I kept hitting limitations. CFFiddle requires a social login to use some features. TryCF doesn't indicate which patch version it's running against. Neither lets you compare engines side-by-side. And both go offline sometimes, usually right when I need them. :(

So I built cfmlFiddle.

What it is

cfmlFiddle is a self-hosted CFML playground. It runs on your machine through CommandBox. You write code in an Ace Editor, pick an engine (or all of them), click Run, and see the output. If you picked multiple engines, you see all the results stacked, side by side, or tabbed.

cfmlFiddle screenshot

The default config ships with 10 server definitions:

  • Adobe ColdFusion 2016, 2021, 2023, 2025
  • Lucee 5, 6, 7
  • BoxLang (native, Adobe compat, Lucee compat)

You start whichever ones you need. Most of the time I run two or three.

The part I actually wanted

My main gripe with the online tools was never being able to pin a version. If I'm debugging something a client reported on CF2021.0.14, I need to know what CF2021.0.14 does, not whatever patch the hosted service happens to be running this week.

With cfmlFiddle, each engine version is a CommandBox server.json file. You control which version is installed, down to the patch. You can keep CF2021.0.14 around for months if you need it, or install CF2025 the day it drops.

The other thing: running code that the hosted services block. File operations, HTTP calls, Java objects, custom tags. cfmlFiddle doesn't restrict anything. It's your machine.

How the comparison works

Click "Run All Online" and cfmlFiddle sends your code to every running engine simultaneously via cfhttp. Each engine executes the same temp file from a shared webroot. The results come back with timing info, the engine name, and the actual patch version, so you can see exactly what ran where.

There's also an "Append" mode. Check the box and each run stacks on top of the previous results, so you can tweak your code and compare iterations without losing the earlier output.

Interactive mode

I wrote a test script with a <form> and immediately realized the form couldn't post back to itself. The result was static HTML in a div. The form action had nowhere to go.

cfmlFiddle now auto-detects forms in your output. When it finds one (or you check the Interactive box), it renders the result in a sandboxed iframe pointing directly at the payload file on the target engine. The form posts back to itself, processes the data, and returns the result. Multi-step scripts just work.

Under the hood

The status bar uses Server-Sent Events instead of polling. The heartbeat checks all engines with raw TCP socket connections (~50ms total for 10 servers) and streams updates to the browser in real time. It falls back to polling if SSE doesn't work on a particular engine.

Config lives in a JSON file above the webroot. You can change settings without editing CFML code.

All the frontend libraries (Ace, jQuery, SweetAlert2, jQuery contextMenu) ship locally in an assets/vendor/ directory. No CDN dependency by default, though you can flip a config switch if you prefer CDN.

Server management is built into the UI. Click the status bar to start, stop, or inspect engines. Left-click any server for a context menu with direct links to its admin panel, homepage, and documentation.

Session management

Every time you run code, cfmlFiddle saves the payload file with a timestamp. Click the Session button in the toolbar to see a list of everything you've run. Click any entry to reload it into the editor. When you're done, Archive All zips everything up and clears the working directory.

I kept losing track of what I'd tested ten minutes ago. Now I just open the session list and pick it.

The smaller stuff

There's a light/dark theme toggle. It picks up your OS preference by default, and the Ace editor switches to match. I bounce between light and dark depending on the time of day, so this was mostly for me.

You can import code from a GitHub Gist URL. Paste the link, it pulls the first file and drops it in the editor. Useful when someone shares a snippet and you want to see what it does on three engines before replying.

Snippets work the other direction too. Save whatever's in the editor as a named file, reload it later from the dropdown.

Each result card has a refresh button that re-executes and updates the timing, plus a dismiss button to toss results you don't need. Small thing, but it adds up when you're iterating.

We also put some work into keyboard accessibility: skip link, visible focus indicators, arrow keys on the splitter, ARIA roles on the toolbar and status bar.

Getting it

cfmlFiddle is open source under the MIT license.

Website: cfmlFiddle.com Source: GitHub

You need CommandBox installed. Clone the repo, edit config.json with your box.exe path, run box task run launchCFMLFiddle, and pick an engine. It opens in your browser.

cfmlFiddle is a myCFML.com project, sponsored by SunStar Media.

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