Why your schedule never leaves your browser
The .mpp is read by code that runs in your browser tab, and the page is not allowed to send it anywhere. Here is how, and how to check.
The reader runs in your tab
Most online .mpp viewers upload the file because the only complete reader of the format, MPXJ, is written in Java, which browsers do not run. This site compiles MPXJ to JavaScript with TeaVM and runs it in a Web Worker in your tab. The file goes from your disk to that worker and nowhere else.
MPXJ is open source under the GNU Lesser General Public License. The compiled module, its licence, the notices of the libraries inside it, and its complete source and build script are published here: the module, its licence, the notices, our build script, patches and shims and MPXJ 16.10.0's source. You may replace the module with your own build. MPXJ's home is https://www.mpxj.org/.
The page cannot send it
Every page is served with a Content-Security-Policy whose connect-src is 'self': the browser refuses any request to another site, whatever the page's code tries.
The requests it does make to this site are listed in its source in one file, and a test fails the build if any other file makes one:
- one page view: this site's host, the page's path and the host of the page that linked you here;
- one count per file opened: its format (for example mpp14) and one word for the result (for example opened or password) — never the file, its name, its size or anything in it;
- the reader module itself, fetched once from this site.
How to check it yourself
- Open your browser's developer tools, Network tab, then drop a file: you will see the module load (the first time) and one small count, and no request carrying the file.
- Or load this page, turn off your network, and drop a file: it still opens, because nothing needs the network after the reader has loaded.
Questions
Is my file uploaded?
No. The file is read in a Web Worker in this tab by MPXJ, an open-source Project file reader compiled to JavaScript. The page's Content-Security-Policy allows requests to this site only, and none of them carries the file. You can check in your browser's developer tools: dropping a file adds no request with its content.
Which versions of Microsoft Project can it open?
It reads .mpp files from Microsoft Project 98 onwards, .mpt templates and .mpx files. Project 2010 and every later version, including 2021, 2024 and Microsoft 365, save the same .mpp format. Project XML (.xml) files are not read yet. It was tested on files saved by Project 98, 2003, 2007, 2010, 2013, 2016 and 2019, from MPXJ's own test suite.
What if the file is password-protected?
It says so and stops. A password-protected .mpp cannot be read without Project; ask the sender for a copy saved without a password.
Can I edit the plan?
No. It is a viewer: it shows the schedule as saved and does not recalculate it or write .mpp files.
Is it free?
Viewing, printing and the CSV export are free, with no account and no limit on the number of files. A laid-out Gantt PDF (page size, date range, columns) and an Excel workbook are not built yet; the export page says what they would be and counts who wants them.
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