Base64 Encoder & Decoder

Encode text to Base64 or decode Base64 strings back to plain text. Supports standard and URL-safe Base64 with UTF-8 encoding. All processing runs locally — no data uploaded.

Base64 Encoder Decoder: Paste text to encode it to Base64, or paste a Base64 string to decode it back to plain text. Supports UTF-8 encoding. Copy the result with one click. Useful for API payloads, data URIs, and email encoding.

Loading Tool...

This tool requires JavaScript to run.

Please enable JavaScript in your browser to use this free online tool. All processing happens locally in your browser for maximum privacy and speed.

Key Takeaways

Encodes any text to Base64 and decodes Base64 back to text
Base64 uses A–Z, a–z, 0–9, +, / and = for padding
Encoding increases size by approximately 33% (3 bytes → 4 characters)
Used in data URIs, email attachments (MIME), and API authentication headers
All encoding/decoding runs locally in your browser

What is Base64 Encoder Decoder?

Base64 Encoder Decoder — A Base64 Encoder/Decoder is a free tool that encodes text into Base64 format and decodes Base64 strings back into readable text.

Encode and decode Base64 online with this free tool. Paste plain text to encode it as Base64, or paste a Base64 string to decode it back to readable text. Supports both standard Base64 (A-Z, a-z, 0-9, +, /) and URL-safe Base64 (replaces + with - and / with _). Useful for API payload debugging, data URI creation, email encoding (MIME), JWT inspection, and embedding binary data in JSON or XML. All encoding and decoding runs locally in your browser — no data is sent to any server.

How to Use Base64 Encoder Decoder

1
Choose encode or decode mode.
2
Paste text or Base64 input into the editor.
3
Enable URL-safe handling when required.
4
Copy the output for your implementation workflow.

Key Features

Bi-directional Base64 conversion

URL-safe mode support

Fast copy workflow

Useful for API and token debugging

Browser-based utility

Use Cases

API request/response debugging

JWT-related base64url checks

Data URI generation and inspection

Encoding checks in integration tests

About Base64 Encoder Decoder

What Base64 Is (and Isn't)

Base64 is a binary-to-text encoding scheme defined in RFC 4648. It converts arbitrary binary data into a 64-character ASCII alphabet (A-Z, a-z, 0-9, +, /) so the data can travel safely through text-only channels — email, HTTP headers, JSON payloads, XML, terminal output. It is NOT encryption. Anyone can decode Base64 in milliseconds without a key. Base64 provides encoding, not protection. If you need confidentiality, encrypt with AES first, then optionally Base64-encode the ciphertext for transport.

How Base64 Works (3 → 4 Expansion)

Base64 reads input 3 bytes (24 bits) at a time, splits those 24 bits into four 6-bit chunks, and looks each chunk up in the 64-character alphabet. When the input length isn't a multiple of 3, the encoder pads with = characters: one = for input ending in 1 byte short, two == for ending 2 bytes short. Size expansion: Base64 output is always 4/3 ≈ 1.33× the input size (plus padding). So a 1 MB image becomes a 1.33 MB Base64 string — important for choosing whether to embed images as data URIs vs separate file requests.

Standard Base64 vs Base64URL

Variant	Alphabet	Padding	Use case
Standard Base64	A-Z a-z 0-9 + /	Yes (=)	Email (MIME), data URIs, PEM certificates, generic encoding
Base64URL	A-Z a-z 0-9 - _	Often stripped	JWT, OAuth tokens, URL query strings, filenames

URL-safe replaces + → - and / → _ because + means "space" in URL query strings and / is a path separator. JWT spec (RFC 7515) requires Base64URL and forbids the = padding.

Common Use Cases

Data URIs: data:image/png;base64,iVBORw0KG... — embed images directly in HTML / CSS / Markdown
Email attachments (MIME): binary attachments encoded as Base64 with 76-char line breaks
HTTP Basic auth: Authorization: Basic dXNlcjpwYXNz (Base64 of "user:pass")
JWT tokens: header and payload Base64URL-encoded, joined with dots
PEM certificates: X.509 / RSA keys are Base64 between BEGIN / END markers
JSON binary fields: binary data Base64-encoded for transport in JSON / XML
QR codes: binary payloads Base64-encoded for printable representation
Browser localStorage: binary blobs (icons, signatures) stored as Base64 strings

When NOT to Use Base64

Don't use Base64 to hide passwords or API keys. Trivially reversible by anyone. Use encryption (AES) or hashing (bcrypt / argon2).
Don't embed large images as data URIs in HTML. The 33% size penalty + lack of HTTP caching makes separate file requests faster for images larger than ~10 KB.
Don't Base64 over a binary-safe channel. Modern HTTP/2 + JSON binary types (with multipart/form-data) handle binary natively — no need to Base64 inflate.
Don't mix encodings. A Base64 string passed to a Base64URL decoder (or vice versa) will fail on + / or - _ characters.

Cross-Language Compatibility

JavaScript: btoa(text) / atob(b64) (ASCII-only; for UTF-8 use TextEncoder + btoa)
Node.js: Buffer.from(text).toString("base64") / Buffer.from(b64, "base64").toString()
Python: base64.b64encode(b"text") / base64.b64decode(b64)
OpenSSL: echo -n text | openssl base64
Shell (Linux/Mac): echo -n text | base64 / echo b64 | base64 -d
PHP: base64_encode($text) / base64_decode($b64)
Go: base64.StdEncoding.EncodeToString([]byte(text))

All produce identical output for the same input — Base64 is fully cross-platform. If output differs between tools, check for line-break handling (some add line breaks every 76 chars per MIME; others don't) and padding behavior.

Frequently Asked Questions

What is Base64 encoding used for?: Base64 is used to encode binary data as ASCII text for transport through text-based protocols. Common uses: data URIs in HTML/CSS, email attachments (MIME), JWT token segments, HTTP Basic auth headers, and embedding binary data in JSON or XML.
Is Base64 the same as encryption?: No. Base64 is an encoding format, not encryption. Anyone can decode Base64 without a key. It provides no security — use proper encryption (AES, RSA) for confidential data.
What is URL-safe Base64?: URL-safe Base64 replaces + with - and / with _ to avoid characters that have special meaning in URLs. It is used in JWTs, URL query parameters, and file names. Some implementations also strip the = padding.
Why does Base64 increase file size?: Base64 converts every 3 bytes of data into 4 ASCII characters, resulting in approximately 33% size increase. This is the trade-off for being able to embed binary data in text formats.
Can I encode files to Base64?: Yes. The tool supports file encoding to Base64, which is useful for creating data URIs (e.g., data:image/png;base64,...) and embedding images in HTML or CSS.
Is this Base64 tool free?: Yes — 100% free, runs locally in your browser, no rate limit, no size limit, no signup. Unlike some tools that gate large-file encoding behind paid tiers, every feature is unlimited here.
How do I encode an image to Base64 for HTML / CSS?: Upload the image in this tool — it produces a data URI like `data:image/png;base64,iVBORw...` ready to paste into an `<img src="...">` tag or `background-image: url(...)` CSS rule. Best for small icons / SVGs / logos under ~10KB; for larger images, separate file requests are faster due to HTTP caching and the 33% Base64 size penalty.
Why does Base64 add about 33% to file size?: Base64 encodes every 3 bytes of input as 4 ASCII characters of output — a 4/3 = 1.33× expansion. So a 1MB file becomes a ~1.33MB Base64 string. This is the cost of being able to embed binary data in text-only channels. For large assets, use multipart/form-data or binary HTTP bodies instead of Base64-in-JSON.
How do I decode a JWT with Base64?: JWTs use Base64URL (note the URL variant, not standard). Split the JWT on dots into three parts; decode each part with URL-safe Base64. The first part is the header (algorithm); the second is the payload (claims). The third is the binary signature — you usually don't decode it. Easier: use our JWT Decoder which does all of this automatically.
What's the difference between Base64 and base64url?: Standard Base64 uses '+' and '/' in its alphabet — but those characters have special meaning in URLs ('+' = space, '/' = path separator). Base64URL replaces them with '-' and '_' so the result is safe to use in URLs, JWT tokens, query strings, and filenames. Base64URL also typically strips the '=' padding. If you decode Base64URL with a standard Base64 decoder, the '-' and '_' chars will cause errors.
Can I decode Base64 from a curl response?: Yes. Copy the Base64 string from the curl output, paste here, and click decode. If the response is JSON with a Base64 field, copy just the string value (without surrounding quotes). For automation, use `curl ... | jq -r '.field' | base64 -d` in the terminal directly.

Loading your tools...

Variant

Alphabet

Padding

Use case

Standard Base64

A-Z a-z 0-9 + /

Yes (=)

Email (MIME), data URIs, PEM certificates, generic encoding

Base64URL

A-Z a-z 0-9 - _

Often stripped

JWT, OAuth tokens, URL query strings, filenames

Frequently Asked Questions

What is Base64 encoding used for?

Base64 is used to encode binary data as ASCII text for transport through text-based protocols. Common uses: data URIs in HTML/CSS, email attachments (MIME), JWT token segments, HTTP Basic auth headers, and embedding binary data in JSON or XML.

Is Base64 the same as encryption?

No. Base64 is an encoding format, not encryption. Anyone can decode Base64 without a key. It provides no security — use proper encryption (AES, RSA) for confidential data.

What is URL-safe Base64?

URL-safe Base64 replaces + with - and / with _ to avoid characters that have special meaning in URLs. It is used in JWTs, URL query parameters, and file names. Some implementations also strip the = padding.

Why does Base64 increase file size?

Base64 converts every 3 bytes of data into 4 ASCII characters, resulting in approximately 33% size increase. This is the trade-off for being able to embed binary data in text formats.

Can I encode files to Base64?

Yes. The tool supports file encoding to Base64, which is useful for creating data URIs (e.g., data:image/png;base64,...) and embedding images in HTML or CSS.

Is this Base64 tool free?

Yes — 100% free, runs locally in your browser, no rate limit, no size limit, no signup. Unlike some tools that gate large-file encoding behind paid tiers, every feature is unlimited here.

How do I encode an image to Base64 for HTML / CSS?

Upload the image in this tool — it produces a data URI like `data:image/png;base64,iVBORw...` ready to paste into an `<img src="...">` tag or `background-image: url(...)` CSS rule. Best for small icons / SVGs / logos under ~10KB; for larger images, separate file requests are faster due to HTTP caching and the 33% Base64 size penalty.

Why does Base64 add about 33% to file size?

Base64 encodes every 3 bytes of input as 4 ASCII characters of output — a 4/3 = 1.33× expansion. So a 1MB file becomes a ~1.33MB Base64 string. This is the cost of being able to embed binary data in text-only channels. For large assets, use multipart/form-data or binary HTTP bodies instead of Base64-in-JSON.

How do I decode a JWT with Base64?

JWTs use Base64URL (note the URL variant, not standard). Split the JWT on dots into three parts; decode each part with URL-safe Base64. The first part is the header (algorithm); the second is the payload (claims). The third is the binary signature — you usually don't decode it. Easier: use our JWT Decoder which does all of this automatically.

What's the difference between Base64 and base64url?

Standard Base64 uses '+' and '/' in its alphabet — but those characters have special meaning in URLs ('+' = space, '/' = path separator). Base64URL replaces them with '-' and '_' so the result is safe to use in URLs, JWT tokens, query strings, and filenames. Base64URL also typically strips the '=' padding. If you decode Base64URL with a standard Base64 decoder, the '-' and '_' chars will cause errors.

Can I decode Base64 from a curl response?

Yes. Copy the Base64 string from the curl output, paste here, and click decode. If the response is JSON with a Base64 field, copy just the string value (without surrounding quotes). For automation, use `curl ... | jq -r '.field' | base64 -d` in the terminal directly.

Base64 Encoder & Decoder

Key Takeaways

What is Base64 Encoder Decoder?

How to Use Base64 Encoder Decoder

Key Features

Use Cases

About Base64 Encoder Decoder

What Base64 Is (and Isn't)

How Base64 Works (3 → 4 Expansion)

Standard Base64 vs Base64URL

Common Use Cases

When NOT to Use Base64

Cross-Language Compatibility

Frequently Asked Questions

Base64 Encoder & Decoder