Source Map Size Analyzer: Free Online Source Map Inspector — How-To Guide

If you ship JavaScript bundles, source maps are the files that connect your minified production code back to the original source. They are also easy to ignore until something goes wrong: a bundle that loads slowly, a map file that is far bigger than expected, or a stack trace that points nowhere useful. ToolsFam's Source Map Size Analyzer gives you a quick, private way to inspect a source map before you dig deeper.

Try it free: Source Map Size Analyzer

What the Tool Does

The Source Map Size Analyzer inspects source map JSON and reports the things that matter at a glance: how many sources the map covers, whether source content is embedded inside the map, and rough weight signals that hint at why a map file is large. It is a first-pass inspection tool, not a replacement for your compiler, CI checks, or production scanners — but it is exactly the check you want before you run those heavier tools.

It works with real input you paste in, offers sample data if you want to see how it behaves first, validates what you enter, and lets you copy the result or download a text report. There is no account to create and nothing to install.

How to Use It, Step by Step

Open the tool at the link above. You will see an input area, sample data, and actions for validating, copying, downloading, and resetting.
Paste your source map JSON into the input area. If you do not have a map handy, load the sample data first to see the kind of output the analyzer produces.
Run the analyzer. Review the findings: the source count, whether embedded source content is present, and the rough weight signals.
Read the weight signals alongside the source count. A map with many sources, or with full source content embedded, will naturally be heavier — the analyzer helps you see which factor is driving the size.
If the input is invalid, check the validation feedback, fix the JSON, and run it again. A single misplaced bracket or truncated paste is the most common cause of a failed check.
Copy the output for a debugging note or code review comment, or download the text report to keep with your QA handoff or documentation example. Use Reset to clear the workspace before your next map.

3 Practical Tips

Check maps before you ship, not after a bug report. A quick inspection during code review catches an oversized or incomplete map while it is still cheap to fix — for example, before a build setting accidentally embeds full sources into a production map.
Compare maps across builds. Run the analyzer on the previous release's map and the new one. If the source count jumps or the weight signal grows sharply, something in the build changed — a new dependency, a different bundler setting, or sources being included that were not before.
Use the report in handoffs. When you pass a bundle issue to QA or another developer, attach the downloaded report instead of describing the map from memory. Source counts and weight signals give the next person a concrete starting point.

FAQ

Does the Source Map Size Analyzer upload my input?

No. The normal workflow runs locally in your browser, so your source map content stays on your device.

Is this a full replacement for CI or production scanners?

No. It is designed for fast local inspection before you run project-specific checks. For regulated production changes, verify final results with your project's own compiler, CI checks, or infrastructure scanner.

Can I copy or download the result?

Yes. Run the tool, then copy the output or download a text report for your notes, review, or handoff.

What if my source map JSON fails validation?

Check for a truncated paste first — large maps are easy to cut off when copying. Then check the JSON structure around the reported error, fix it, and run the analyzer again.

Privacy Note

The Source Map Size Analyzer runs 100% in the browser — your files never leave your device. There is no upload, no account, and no server-side processing of your source map.

Try it free: Source Map Size Analyzer