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Base64 Decoder

Decode Base64 strings back to plain text instantly online. Free Base64 decoder with full UTF-8 support. No signup required.

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Base64 decoding reverses the encoding process: it converts the 64-character ASCII representation back into the original binary data or text string. RFC 4648 defines the canonical alphabet and padding rules (= characters align output to 3-byte boundaries). Decoders must handle both standard (+/) and URL-safe (-_) variants.

Developers encounter Base64-encoded payloads constantly: reading JWT token claims, inspecting SMTP email bodies with attachments, examining PEM certificates, or debugging API responses that embed binary blobs. Decoding is necessary to view the human-readable content hidden inside these encoded strings.

This tool decodes Base64 in the browser using atob() to convert the Base64 string back to a byte sequence, then passes the result through the TextDecoder API with UTF-8 encoding to reconstruct the original text. This two-step approach correctly handles multibyte characters that a direct atob() string interpretation would corrupt.

Common Use Cases

Inspecting JWT token claims

A JWT consists of three Base64url-encoded segments separated by dots. The second segment is the payload containing claims like user ID, roles, and expiry timestamp. Developers debugging authentication issues in systems using Auth0, Keycloak, or custom JWTs need to decode this segment to verify what the server is actually asserting about the user.

Reading PEM certificate contents

PEM files (used by nginx, Apache, and OpenSSL) wrap Base64-encoded DER certificate data between -----BEGIN CERTIFICATE----- markers. When auditing a TLS certificate's subject, expiry, or Subject Alternative Names without running openssl x509 -text, decoding the inner Base64 block reveals the raw DER bytes for further parsing.

Decoding email attachments in SMTP logs

SMTP and MIME email bodies encode attachments and HTML parts as Base64. When debugging email delivery issues in Postfix or examining raw .eml files exported from Gmail or Outlook, the attachment content appears as a Base64 block. Decoding reveals whether the correct file was attached and whether encoding was applied correctly.

Extracting secrets from CI environment variables

Service account keys, API certificates, and SSH private keys stored in GitHub Actions secrets or HashiCorp Vault are often Base64-encoded for safe storage. When rotating credentials or auditing what a particular encoded secret actually contains, Base64 decoding the value confirms the embedded JSON structure or key format before use.

How to Use the Base64 Decoder

  1. Paste your Base64-encoded string in the left panel.
  2. The decoded text appears instantly in the right panel.
  3. Click "Copy Output" to copy the decoded result.
  4. Use "Load Example" to see a sample decoding.
  5. Whitespace in the input is automatically stripped.

Common Use Cases