View certificate files (PEM, CRT, CER, DER)
Check a certificate's subject, issuer, validity, expiry, and fingerprint — including Korean NPKI signCert.der.
Drop a folder or files here
JPG · PNG · WebP · GIF · BMP · AVIF · SVG · HEIC · PSD · AI · TIFF · camera RAW · PDF · HWP · Word · PPT · Excel · DWG/DXF · MP4/WebM/MOV/MKV/AVI/WMV · MP3/WAV/WMA/AIFF · TXT/MD/CSV/JSON/HTML — subfolders included
This browser doesn't support the folder-open dialog, so the standard folder picker is used. Files are read only on your device.
Viewer pages by format
Popular formats have their own page. Whichever page you are on, files of any other supported format open just the same.
- View HEIC photosHEIC·HEIF·HIF
- View PSD filesPSD·PSB
- View AI filesAI
- View TIFF filesTIF·TIFF
- View camera RAW photosCR2·CR3·CRW·NEF…
- Play MKVMKV
- Play AVI and DivXAVI·DIVX
- Play RMVB and RMRM·RMVB
- Play WMVWMV·ASF
- Play FLVFLV
- Play TS and M2TSTS·M2TS·MTS
- Play WMAWMA
- Play APE and lossless audioAPE·WV·TTA·MPC
- Open EML and MSG emailEML·MSG
- Read EPUB ebooksEPUB
- View Jupyter notebooks (ipynb)IPYNB
- Open legacy Word (.doc)DOC
- View DICOM medical imagesDCM·DICOM·DIC
- View STL and OBJ 3D modelsSTL·OBJ
- Open ZIP and TAR archivesZIP·TAR·TGZ·GZ…
- Read CBZ comicsCBZ
- View certificate files (PEM, CRT, CER, DER)PEM·CRT·CER·DER…
- View SRT and SMI subtitlesSRT·VTT·SMI·SAMI…
- Preview font files (TTF, OTF, WOFF)TTF·OTF·WOFF·WOFF2…
Word, PowerPoint, Excel, HWP, and CAD have their own document viewer pages. Full file viewer →
Double-clicking a PEM, CRT, CER, or DER file opens the OS certificate manager, and in the middle of a server setup you often just want to know what a certificate is and when it expires. This page opens certificates and shows subject, issuer, validity, expiry status, SAN, public key, and fingerprint at a glance — including signCert.der from a Korean NPKI folder.
How to use it
- 1Click 'Choose PEM files' or drop a certificate folder (such as NPKI) onto the page.
- 2Click a file in the grid to see its card — subject (CN, organization), issuer, validity with a valid/expired badge, SAN domains, public key type, signature algorithm, serial number, and SHA-256 fingerprint.
- 3Chain PEMs (several certificates) show every certificate in order. ← → moves to other files.
What it shows
PEM text (-----BEGIN CERTIFICATE-----) and DER binary (.cer, .der) are both parsed by an in-house ASN.1 reader covering X.509 v1–v3. RSA shows its bit size (2048, 4096), EC its curve (P-256, P-384), and CA certificates get a CA badge. Fingerprints are computed with the browser's WebCrypto. signCert.der from a Korean NPKI folder is ordinary X.509, so it opens as-is with its expiry visible.
Files are read inside the browser only and never sent anywhere. Close the tab and nothing remains.
Private keys are never shown
A file containing a PRIVATE KEY block (.key, signPri.key, and the like) shows only a 'private key file' warning — the key value is never put on screen. A CSR (certificate signing request) gets a 'request file' notice only. It's designed so a shared screenshot can't leak a secret.
Limits
PFX/P12 (password bundles) aren't supported yet. Chain validation (whether to trust it) isn't performed — contents only. Revocation (CRL/OCSP) isn't checked.
Frequently asked questions
How do I check a Korean NPKI certificate's expiry?+
Open signCert.der from the NPKI folder (Windows: C:\Users\<you>\AppData\LocalLow\NPKI, or the NPKI folder on a USB stick) under a subfolder such as yessign. The validity period is shown; no password is needed.
What happens if I open signPri.key?+
Only a private-key warning appears; the contents are not displayed. Never share that file with anyone.
Does it tell me whether to trust the certificate?+
No. It shows contents such as issuer and expiry, without chain validation or revocation checks. Use the browser's padlock or openssl verify for that.
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