Base64 Decode
Free Base64 Decoder Online
About Base64 Decode
Base64 Decode is a free, instant, browser-based tool that converts Base64 encoded strings back to their original text or binary content. If you have received Base64 encoded data and need to see what it actually contains, this tool decodes it immediately — entirely within your browser, with no server interaction.
Base64 decoding is essential for developers working with authentication systems, APIs, email protocols, and data storage. JSON Web Tokens (JWTs) store their header and payload as Base64URL encoded JSON — decoding these sections reveals the token issuer, subject, expiration time, permissions, and other claims. API credentials in environment files or CI/CD secrets are frequently stored as Base64 encoded strings for obfuscation. Email message bodies and attachments are transmitted as Base64 encoded MIME parts in SMTP. Many APIs return Base64 encoded file content, thumbnails, or binary data in JSON responses.
The tool automatically handles both standard Base64 (using the + and / characters) and URL-safe Base64, also called Base64URL (using the - and _ characters), which is used by JWT, OAuth, and other web authentication standards. It correctly handles strings with or without padding characters (=) at the end, decoding both padded and unpadded variants accurately.
Base64 decoding is essential for developers working with authentication systems, APIs, email protocols, and data storage. JSON Web Tokens (JWTs) store their header and payload as Base64URL encoded JSON — decoding these sections reveals the token issuer, subject, expiration time, permissions, and other claims. API credentials in environment files or CI/CD secrets are frequently stored as Base64 encoded strings for obfuscation. Email message bodies and attachments are transmitted as Base64 encoded MIME parts in SMTP. Many APIs return Base64 encoded file content, thumbnails, or binary data in JSON responses.
The tool automatically handles both standard Base64 (using the + and / characters) and URL-safe Base64, also called Base64URL (using the - and _ characters), which is used by JWT, OAuth, and other web authentication standards. It correctly handles strings with or without padding characters (=) at the end, decoding both padded and unpadded variants accurately.
starKey Features
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Standard and URL-safe Base64 Decoding
Automatically detects and handles both standard Base64 and URL-safe Base64URL encoding, including variants with and without = padding characters.
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UTF-8 Unicode Text Recovery
Correctly decodes Base64 encoded UTF-8 strings, recovering the original Unicode text including accented characters, Chinese, Japanese, Arabic, and emoji.
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Input Validation and Error Reporting
Validates that your input contains only valid Base64 characters before decoding. Reports clear error messages for invalid characters or incorrect string length.
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Instant Real-time Decoding
Decodes Base64 strings in real time as you type or paste them, with immediate feedback in the output area — no button click required for quick inspection.
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Complete Browser Privacy
All decoding happens in your browser JavaScript engine. JWT tokens, API credentials, and encoded sensitive data are never transmitted to any external server.
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JWT Payload Inspection
Paste the middle section of any JWT token (between the two dots) to instantly see the decoded JSON claims — user ID, roles, expiry, issuer, and custom claims.
help_outlineHow to Use
1
Paste Your Base64 String
Paste the Base64 encoded string you want to decode into the input textarea. For JWT tokens, paste only the header (before first dot) or payload (between the two dots) section.
2
Click Process
Press the Process button. The tool decodes the Base64 string and displays the original text or data in the output area.
3
Review the Decoded Output
Check the decoded text in the output area. For JWT payloads, you should see readable JSON. For encoded text, you should see the original string.
4
Copy the Result
Use the Copy button to copy the decoded content to your clipboard for further analysis, debugging, or documentation.
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JWT Token Debugging
Decode the header and payload sections of JSON Web Tokens to inspect authentication claims, check expiration timestamps, verify issued-at times, and debug authorization issues.
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Email Content Decoding
Decode Base64 encoded email message bodies or binary attachment data received via IMAP or POP3 when reviewing raw email messages in text form.
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API Response Data Extraction
Decode Base64 encoded fields returned by third-party APIs that embed file content, thumbnails, documents, or binary data as Base64 strings within JSON responses.
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Credential and Secret Inspection
Safely decode Base64 encoded credentials, tokens, or configuration secrets stored in environment files to verify their content — entirely within your browser without network exposure.