🗂️ Base64 to File Converter – Decode Any Base64 String to a Downloadable File
The Base64 to File Converter decodes a Base64-encoded string back into its original binary file and triggers an instant browser-side download. Whether you're working with embedded assets in JSON APIs, MIME email attachments, Data-URI blobs, database BLOB exports, or JWT payloads, this tool recovers the original file in one click — entirely in your browser, with no data ever sent to a server.
What Is Base64 Encoding?
Base64 is a binary-to-text encoding scheme (RFC 4648) that represents binary data using only 64 printable ASCII characters: A–Z, a–z, 0–9, +, and /, with = used for padding. Every 3 bytes of binary data expand to 4 Base64 characters, adding approximately 33% size overhead. This predictable, reversible encoding makes it safe to embed binary data inside text-based formats like HTML, JSON, XML, and email.
Supported Input Formats
The tool automatically detects and handles four common Base64 variants — paste any of them and the decoder normalises it transparently:
| Format | Description | Example |
|---|---|---|
| Standard Base64 | RFC 4648 §4 — uses + and / | SGVsbG8gV29ybGQ= |
| URL-safe Base64 | RFC 4648 §5 — replaces +→-, /→_ | SGVsbG8gV29ybGQ |
| MIME / Line-wrapped | RFC 2045 — line breaks every 76 characters (email attachments) | SGVsbG8g
V29ybGQ= |
| Data-URI | Full data:<mime>;base64, prefix auto-stripped | data:image/png;base64,iVBO… |
Magic-Byte File Type Detection
After decoding, the tool inspects the first few bytes of the binary data — known as magic bytes or file signatures — to identify the file format automatically. For example, a PNG file always starts with 89 50 4E 47 and a PDF with 25 50 44 46. Detected formats include:
Hex Dump Preview
The hex preview panel shows the first 256 decoded bytes as a formatted hex dump — 16 bytes per row — alongside their printable ASCII equivalents (non-printable bytes appear as .). This is invaluable for verifying file integrity, confirming magic bytes, and debugging unexpected or corrupted Base64 payloads.
How to Use This Tool
- Paste your Base64 string into the input area. You can paste raw Base64, a Data-URI, URL-safe Base64, or MIME line-wrapped content — the format is detected automatically.
- Review the detected MIME type and optionally override it. The tool proposes a filename based on the detected format.
- Click "Decode & Download" to save the decoded file to your downloads folder. The download is triggered instantly via a temporary object URL — no server involved.
- Inspect the hex preview to verify the binary content of the decoded file.
Common Use Cases
- API debugging — recover binary files embedded as Base64 strings in JSON API responses (e.g., PDF reports, generated images, exported spreadsheets).
- Email attachments — decode MIME-encoded attachments copied from raw email source.
- JWT inspection — extract and save binary payloads encoded in URL-safe Base64 within JSON Web Tokens.
- Database exports — convert BLOB columns exported as Base64 strings back into their original files.
- Configuration payloads — decode embedded certificates, keys, or assets stored as Base64 in YAML, TOML, or environment variables.
Privacy & Security
All decoding happens entirely in your browser using the native atob() function and the Web File API. No Base64 data, no decoded bytes, and no filenames are ever transmitted to any server. This makes the tool safe for sensitive documents, private keys, and confidential payloads.
Understanding Encoding Overhead
Base64 encodes every 3 bytes as 4 characters, producing a 33.3% size increase. A 1 MB file becomes roughly 1.37 MB when Base64 encoded. The tool displays both the encoded length and the decoded byte size so you can confirm the expected overhead. The formula is:
decoded_bytes = floor(base64_length * 3 / 4) - padding_chars
overhead_pct = (base64_length / decoded_bytes - 1) × 100%This tool is completely free, runs offline, and works on all modern browsers including Chrome, Firefox, Safari, and Edge.