OpenAnyFile
Works
Viewing, inspecting and verifying. You get the full text content with encoding detection. File details, exact byte size and the detected signature are always shown.
How to open a .cer file
A CER file is a Certificate File, introduced by Microsoft / IETF in 1988. Below: what is actually inside one, and how to open it without installing special software.
What is a .cer file?
Certificate File is a text & markup format developed by Microsoft / IETF, first appearing in 1988. It is normally produced by Windows certificate store.
The Windows spelling of .crt. Same X.509 content, and the same PEM-or-DER ambiguity.
| Full name | Certificate File |
|---|---|
| File category | Text & markup |
| MIME type | application/pkix-cert |
| Magic bytes (file signature) | 30 82 or 2D 2D 2D 2D 2D |
| Developer | Microsoft / IETF |
| Introduced | 1988 |
| Usually created by | Windows certificate store |
| OpenAnyFile engine | plain text reader |
| Opens without upload | Yes — parsed locally in your browser |
Open a .cer file in your browser
OpenAnyFile routes .cer to its plain text reader, which displays the full text content with encoding detection.
- Open the OpenAnyFile opener in this browser — nothing to download or sign up for.
- Drag your .cer file onto the drop zone, click to browse for it, or paste it with Ctrl+V.
- The extension is detected and the file is handed to the plain text reader.
- Your CER opens on its own viewer page: the full text content with encoding detection.
- Use fullscreen for a closer look, or download the file back out unchanged. Free, and free in the sense that there is no paid tier waiting behind step three.
What you can and cannot do with it here
Does not work
Editing and re-saving. OpenAnyFile is a reader, not an editor — for changes you still need special software or an equivalent.
Your {ext} file stays on your device
The entire pipeline — detection, decoding, rendering — runs client-side. Your browser hands the bytes to a decoder compiled to WebAssembly, the result is drawn to the page, and that is the whole journey. No account is created, no file is stored, and no analytics event carries your filename. This is also why there is no size limit imposed by a server: the only ceiling is your own available memory.
Frequently asked questions about CER files
Can I open a .cer file without installing special software?
Yes. OpenAnyFile's plain text reader runs in your browser, so you can read a CER file with nothing installed. You get the full text content with encoding detection. For full editing you still need the original application — this is a viewer, not an editor.
How can I check a file really is a CER file?
Look at the first bytes rather than the extension. A genuine CER begins with 30 82 or 2D 2D 2D 2D 2D. Opening the file in OpenAnyFile shows that signature in the file-details panel, so a file renamed to .cer by mistake is easy to spot.
Is it safe to open a CER file online?
With OpenAnyFile, yes, because nothing is uploaded. The file is read locally through your browser's File API and never leaves your device, so there is no server copy to leak, log or retain. That matters most for the kind of file people are least willing to hand to a random converter site.
What is a .cer file, exactly?
Certificate File — an application/pkix-cert format created by Microsoft / IETF since 1988. The Windows spelling of .crt. Same X.509 content, and the same PEM-or-DER ambiguity.
Does the same viewer handle formats related to CER?
Yes — the same engine also opens .dat, .srt, .crt, so you can compare related files without switching tools.
Related formats
These open with the same engine, so if you have one of these sitting next to your .cer file, it will open too: