Decode and display certificate details from PEM format.
X.509 Certificate Decoder works entirely in the browser tab. Open it, use it, close it. Nothing about the session outlives the page.
The page holds your input in memory and nowhere else. No cookie stores it, no request sends it, and a reload wipes it.
You will find it under Keys & certificates, alongside 7 other tools for the same sort of job.
Shows subject, issuer, validity dates, and signature algorithms.
-----BEGIN CERTIFICATE----- MIIDlzCCAn+gAwIBAgIUFwm+2kRILn+VmnrTSg8OXEeqdzYwDQYJKoZIhvcNAQEL BQAwWzELMAkGA1UEBhMCR0IxDzANBgNVBAgMBkxvbmRvbjEPMA0GA1UEBwwGTG9u ZG9uMRQwEgYDVQQKDAt1dGlscyB0b29sczEUMBIGA1UEAwwLZXhhbXBsZS5jb20w HhcNMjYwODI0MDkxODIyWhcNMzYwODIxMDkxODIyWjBbMQswCQYDVQQGEwJHQjEP MA0GA1UECAwGTG9uZG9uMQ8wDQYDVQQHDAZMb25kb24xFDASBgNVBAoMC3V0aWxz IHRvb2xzMRQwEgYDVQQDDAtleGFtcGxlLmNvbTCCASIwDQYJKoZIhvcNAQEBBQAD ggEPADCCAQoCggEBAM23MeLX4/CvpV8xnu4oaVDvAGUirUyFjkCBHgmEI56Mb9Bh ga/RlPb4i2V71HQ4uMHmZKMlwSRm3S7FtjraaLXLDFJNjEc8ROtQQd0FCQZSCvIe Eo5hxq68EBW6OPHypw6+yP7JNe00ZopfeHeoQLBocsqCTqpUKeICebUWaXcMM2Db zDpu442JE8k0NqvicsNQw3psItBka7bgd3Ig9DoJfwfJVPLnpCvL6tog4i1x+iVi /fe5SzSSQa/6B+zW4W6TQ0dg2e1QOJVMjzQwbF5/fblRcNLnqO0q5TntWbs+10Mt cXaKyEi36eGRVJOSGn9CcpMrCS1AOLtJSfklBVcCAwEAAaNTMFEwHQYDVR0OBBYE FHAaEZ0cFkjcappsVbK6zDoov2X0MB8GA1UdIwQYMBaAFHAaEZ0cFkjcappsVbK6 zDoov2X0MA8GA1UdEwEB/wQFMAMBAf8wDQYJKoZIhvcNAQELBQADggEBAD43WlYO i0b7u+zVUZIvK0C8fvgEsxaaJNAH1eNrMVDaTxOY4Eygrbf5C+mLVQvkjagpqRMK 2Ph4dv15FqBIcFWycSKgsvgelovTCsomiXVEucY6Et/9zaf4NECkJFEJ08On0GGf IBMnjb4Bkq5TsJb2CbLGXeS/D0TpOjqkHYEaNe1ya+71XxGMxkGNB9IKWx1R/TSc biD6oqmfP3u5sVgHPDCM8qXsWUVTjIK/htqsrYZ1xPVhjV1Q6KWOEYB4WXw4Zgdm DdtH1+MZ1RDhKQZVnxH8h8zOVC0XKbHlqRvp3SVN/0oD4vXBNGj1YCTq1jWvtLR4 QXAgDhOy8ES7xfQ= -----END CERTIFICATE-----
=== X.509 Certificate === Total size: 923 bytes Not Before: 2026-08-24 09:18:22 UTC Not After: 2036-08-21 09:18:22 UTC Algorithms: SHA-256 with RSA, C, ST, L, O, CN, RSA, Subject Key Identifier, Authority Key Identifier, Basic Constraints SHA-256 Fingerprint: (use SHA-256 Hash tool on the DER bytes)
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No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.
Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.
Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.
Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.