How do I decode a PEM certificate?

Paste it into the box, including the BEGIN CERTIFICATE and END CERTIFICATE lines, and the fields appear in the decoded pane as you type. You can also press Open file and pick a .pem, .crt, .cer or .der file, or drag the file onto the dark panel. A text file is read as it is; a binary DER file is turned back into base64 and shown in the box, so what the page decoded is always visible to you. A certificate copied out of a log line or a JSON field with no BEGIN and END lines around it still works: the text is read as base64 DER, and the page says that is what it did. One reading takes up to 200,000 characters, which is a chain many times over.

Does a certificate that decodes here mean it is valid?

No. Decoding reads the fields. This page does not verify the signature, build or validate a trust chain, check revocation through OCSP or CRLs, or compare an expected hostname. Expired certificates, untrusted certificates and certificates for another domain can all decode cleanly. Date status refers only to the not-before/not-after window and the device clock; it is not a security or trust result.

What is the SHA-256 fingerprint, and is it the same one my browser shows?

It is the SHA-256 digest of the certificate's own DER bytes, which is the same value openssl prints for -fingerprint -sha256 and the same one a browser shows in its certificate viewer. That is what makes it useful: it identifies this exact certificate, so you can tell whether the file on your laptop is the one the server is actually sending, or whether two copies of a certificate are the same. You can switch between the colon separated form and the plain hex form, and copy either. The digest is computed in this tab from the bytes you pasted, and the tests compare it against the SHA-256 in Node's standard library on every run.

What happens if I paste a private key with the certificate?

Nothing is decoded and nothing is kept. A .pem bundle often holds the key and the certificate together, and people paste the whole file by habit, so any BEGIN PRIVATE KEY, BEGIN RSA PRIVATE KEY, BEGIN ENCRYPTED PRIVATE KEY or BEGIN OPENSSH PRIVATE KEY block is refused by its label before any body is read. The message names the block it found and never echoes the key material back, and the check runs a second time before anything is written to this browser, so key material cannot reach storage even by accident. Paste only the part between BEGIN CERTIFICATE and END CERTIFICATE.

Can it read a whole chain, or a certificate signing request?

A chain, yes: paste every block and each certificate is decoded in the order it appears, with a numbered control for moving between them and a separate fingerprint for each. Nothing here checks that they chain together, and the page says so. A certificate signing request is a different thing, and it is refused with that in the message: a CSR is what you send to a certificate authority, and the certificate is what comes back. A public key block, a CRL and a PKCS#7 bundle are each named the same way rather than being read as a certificate.

Why does my certificate say there is no SAN?

It has no subject alternative name extension. Modern browsers use SANs for hostname matching rather than a CN alone. This page lists DNS, IP, email and URI names when present. It also reports weak-key/signature observations, equal issuer and subject names, and the lifetime written in the dates. Equal names mean self-issued by name; they do not prove self-signing or root trust. Public-TLS validity limits depend on issuance date and CA policy, which this decoder does not validate.

How is expiry worked out?

From the two dates in the certificate, read exactly as written and shown in full. A UTCTime carries a two digit year and follows the RFC 5280 rule, where 00 to 49 means 2000 to 2049 and 50 to 99 means 1950 to 1999; a date past 2049 is written as a GeneralizedTime with its year in full, and both are handled. The window is inclusive: the certificate is in date up to the last millisecond of its not-after time, and expired one millisecond later, and the page counts whole days either way. A date that is not a date, a month 13 or a minute 61, is refused with the characters it read rather than being turned into a number. The displayed device clock refreshes every 30 seconds and whenever you replace the certificate. Changing the device clock can change this date-only status.

Is my certificate uploaded, or remembered?

Nothing is uploaded and nothing is sent anywhere: the parsing, the decoding and the fingerprint all happen in this tab. A certificate is public by design, so what you paste is kept in this browser alone and is still here when you come back, and the Start over button above the tool forgets it. Two things are never kept: anything holding a private key, and a paste longer than 40,000 characters, which is read and decoded in full but not written to storage. If your browser blocks storage entirely, everything on the page still works and nothing is remembered between visits.

Can this decode a SAML certificate or a PEM key?

An X.509 certificate extracted from an X509Certificate element in SAML metadata can be pasted as its Base64 DER body, or with BEGIN CERTIFICATE lines. This page reads that certificate’s fields and fingerprint. It does not parse SAML XML, validate a SAML response or signature, or test an identity-provider configuration. PEM is an envelope used for many objects: a private key is refused, a public-key block is not a certificate, and a CSR belongs in CSR Decoder.

Can this read a PFX bundle or check a live SSL server?

It reads certificate text or local DER files. It does not decrypt PKCS#12/PFX bundles, unpack PKCS#7, connect to a hostname, fetch a server chain or perform an SSL Labs-style check. Export the public certificate as PEM or DER first; keep private keys on your own machine.

Certificate Decoder

Paste the certificate and the fields are on the first screen: the PEM in one pane, the decoded subject, issuer, dates, SAN and SHA-256 fingerprint in the decoded pane, with the serial in hex and in decimal, the key algorithm and size, and every extension listed by name, OID and critical flag. The reading is done by a bounded DER parser in this tab: nothing is uploaded, there is no account, and no sign-up stands in front of it. Two things here are deliberately different from the pages already on this search. A private key pasted along with the certificate is refused by its label before a single byte is decoded, and it is never written to this browser. And decoding is never dressed up as checking: this page does not verify a signature, build a chain, ask an OCSP responder or compare a hostname, so it says so rather than showing a tick that would mean nothing. Paste a full chain and every certificate in it is decoded in order, each with its own fingerprint.

certificate.pem1,402 characters

decodedX.509 v3

subject    CN=example.com, O=Example Ltd, L=Somerville, ST=Massachusetts, C=US
issuer     CN=Example Root CA, O=Gizmobench Example, C=US
not before 2026-09-21
not after  2036-09-18
SAN        example.com, www.example.com, 192.0.2.10
serial     0a:1b:2c:3d:4e:5f:60:71:82:93
key        RSA 2048 bit
signed     sha256WithRSAEncryption
SHA-256    45:1e:f8:67:51:b7:f9:24:7c:3b:80:86:59:c1:19:58:bf:2f:5e:18:7f:95:32:94:34:ba:7c:f6:cc:88:8b:55

Subject

example.com

Expires

2036-09-18

SANs

Version

X.509 v3

example.com, issued by Example Root CA, not in date until 2026-09-21. SHA-256 45:1e:f8:67:51:b7:f9:24:7c:3b:80:86:59:c1:19:58:bf:2f:5e:18:7f:95:32:94:34:ba:7c:f6:cc:88:8b:55.

Fingerprint

What is in it

Field	Value
Subject	CN=example.com, O=Example Ltd, L=Somerville, ST=Massachusetts, C=US
Issuer	CN=Example Root CA, O=Gizmobench Example, C=US
Serial	0a:1b:2c:3d:4e:5f:60:71:82:93 47724914708969405121171 in decimal
Not before	2026-09-21T00:51:00Z
Not after	2036-09-18T00:51:00Z
Public key	RSA 2048 bit
Signed with	sha256WithRSAEncryption
SHA-256	45:1e:f8:67:51:b7:f9:24:7c:3b:80:86:59:c1:19:58:bf:2f:5e:18:7f:95:32:94:34:ba:7c:f6:cc:88:8b:55
Size	994 bytes of DER

Names this certificate carries

Type	Name
DNS	example.com
DNS	www.example.com
IP	192.0.2.10

Extensions

Extension	What it says
Basic constraints 2.5.29.19 critical	Not a CA: this certificate may not sign other certificates.
Key usage 2.5.29.15 critical	Digital signature, Key encipherment
Extended key usage 2.5.29.37	TLS server authentication, TLS client authentication
Subject alternative name 2.5.29.17	DNS:example.com, DNS:www.example.com, IP:192.0.2.10
Subject key identifier 2.5.29.14	3b:70:c3:97:c9:be:30:64:1f:83:b9:e7:37:bc:a9:f9:d3:fd:ac:b9
Authority key identifier 2.5.29.35	2b:26:4e:1d:41:c9:d5:39:12:e9:d8:d8:23:1e:26:4c:dc:2e:7a:bf

Its lifetime is 3,650 days. Public-TLS limits depend on the issuance date and CA policy; this decoder does not check that policy, issuance history or public root-store membership.

Valid PEMone certificate
subject, issuer, dates, SAN
Expired certificatepast not-after
dates shown, expiry flagged
Not a certificaterandom base64
refused, says what it read

Decoded is not checked. Nothing on this page checks a signature, a chain, revocation or a hostname. Those are the four things a browser does after it decodes one: it checks the signature against the issuer's key, builds a chain up to a root the machine keeps, asks whether the certificate has been revoked, and matches the hostname. A page with no network and no root store cannot do the middle two at all, and doing the other two alone would put a tick on this page that covered a quarter of the question. So an expired certificate, a self-signed one and a certificate for somebody else's domain all decode here exactly as cleanly as the one your server is using, and the fields above are how you tell them apart.

Up to 200,000 characters in one reading, which is a certificate chain many times over. PEM or raw DER, pasted or opened from the file, read in this tab with no upload and no account. A private key pasted with the certificate is refused before anything is decoded and is never written to this device; the certificate itself is kept in this browser so it is still here when you come back, and the Start over button above the tool forgets it.

Accuracy. Decodes the fields the certificate actually contains and shows them unchanged, including the SHA-256 fingerprint. It reads the file in your browser and does not check any trust chain, revocation or hostname, so a certificate decoding cleanly here is not a certificate a browser would accept.

Common questions

How do I decode a PEM certificate?: Paste it into the box, including the BEGIN CERTIFICATE and END CERTIFICATE lines, and the fields appear in the decoded pane as you type. You can also press Open file and pick a .pem, .crt, .cer or .der file, or drag the file onto the dark panel. A text file is read as it is; a binary DER file is turned back into base64 and shown in the box, so what the page decoded is always visible to you. A certificate copied out of a log line or a JSON field with no BEGIN and END lines around it still works: the text is read as base64 DER, and the page says that is what it did. One reading takes up to 200,000 characters, which is a chain many times over.
Does a certificate that decodes here mean it is valid?: No. Decoding reads the fields. This page does not verify the signature, build or validate a trust chain, check revocation through OCSP or CRLs, or compare an expected hostname. Expired certificates, untrusted certificates and certificates for another domain can all decode cleanly. Date status refers only to the not-before/not-after window and the device clock; it is not a security or trust result.
What is the SHA-256 fingerprint, and is it the same one my browser shows?: It is the SHA-256 digest of the certificate's own DER bytes, which is the same value openssl prints for -fingerprint -sha256 and the same one a browser shows in its certificate viewer. That is what makes it useful: it identifies this exact certificate, so you can tell whether the file on your laptop is the one the server is actually sending, or whether two copies of a certificate are the same. You can switch between the colon separated form and the plain hex form, and copy either. The digest is computed in this tab from the bytes you pasted, and the tests compare it against the SHA-256 in Node's standard library on every run.
What happens if I paste a private key with the certificate?: Nothing is decoded and nothing is kept. A .pem bundle often holds the key and the certificate together, and people paste the whole file by habit, so any BEGIN PRIVATE KEY, BEGIN RSA PRIVATE KEY, BEGIN ENCRYPTED PRIVATE KEY or BEGIN OPENSSH PRIVATE KEY block is refused by its label before any body is read. The message names the block it found and never echoes the key material back, and the check runs a second time before anything is written to this browser, so key material cannot reach storage even by accident. Paste only the part between BEGIN CERTIFICATE and END CERTIFICATE.
Can it read a whole chain, or a certificate signing request?: A chain, yes: paste every block and each certificate is decoded in the order it appears, with a numbered control for moving between them and a separate fingerprint for each. Nothing here checks that they chain together, and the page says so. A certificate signing request is a different thing, and it is refused with that in the message: a CSR is what you send to a certificate authority, and the certificate is what comes back. A public key block, a CRL and a PKCS#7 bundle are each named the same way rather than being read as a certificate.
Why does my certificate say there is no SAN?: It has no subject alternative name extension. Modern browsers use SANs for hostname matching rather than a CN alone. This page lists DNS, IP, email and URI names when present. It also reports weak-key/signature observations, equal issuer and subject names, and the lifetime written in the dates. Equal names mean self-issued by name; they do not prove self-signing or root trust. Public-TLS validity limits depend on issuance date and CA policy, which this decoder does not validate.
How is expiry worked out?: From the two dates in the certificate, read exactly as written and shown in full. A UTCTime carries a two digit year and follows the RFC 5280 rule, where 00 to 49 means 2000 to 2049 and 50 to 99 means 1950 to 1999; a date past 2049 is written as a GeneralizedTime with its year in full, and both are handled. The window is inclusive: the certificate is in date up to the last millisecond of its not-after time, and expired one millisecond later, and the page counts whole days either way. A date that is not a date, a month 13 or a minute 61, is refused with the characters it read rather than being turned into a number. The displayed device clock refreshes every 30 seconds and whenever you replace the certificate. Changing the device clock can change this date-only status.
Is my certificate uploaded, or remembered?: Nothing is uploaded and nothing is sent anywhere: the parsing, the decoding and the fingerprint all happen in this tab. A certificate is public by design, so what you paste is kept in this browser alone and is still here when you come back, and the Start over button above the tool forgets it. Two things are never kept: anything holding a private key, and a paste longer than 40,000 characters, which is read and decoded in full but not written to storage. If your browser blocks storage entirely, everything on the page still works and nothing is remembered between visits.
Can this decode a SAML certificate or a PEM key?: An X.509 certificate extracted from an X509Certificate element in SAML metadata can be pasted as its Base64 DER body, or with BEGIN CERTIFICATE lines. This page reads that certificate’s fields and fingerprint. It does not parse SAML XML, validate a SAML response or signature, or test an identity-provider configuration. PEM is an envelope used for many objects: a private key is refused, a public-key block is not a certificate, and a CSR belongs in CSR Decoder.
Can this read a PFX bundle or check a live SSL server?: It reads certificate text or local DER files. It does not decrypt PKCS#12/PFX bundles, unpack PKCS#7, connect to a hostname, fetch a server chain or perform an SSL Labs-style check. Export the public certificate as PEM or DER first; keep private keys on your own machine.

Decodes the fields the certificate actually contains and shows them unchanged, including the SHA-256 fingerprint. It reads the file in your browser and does not check any trust chain, revocation or hostname, so a certificate decoding cleanly here is not a certificate a browser would accept.