Base64 & URL Encoder / Decoder

How to use it

1. Pick the Base64, URL or JSON tab.
2. Paste your input and choose Encode or Decode (for Base64, also choose Standard or URL-safe).
3. Copy the output. Invalid input — for example a Base64 string with illegal characters, or a malformed % sequence — shows a clear error instead of garbage output.

When to use which encoding

• Base64 — to carry binary or arbitrary text through text-only channels: data URIs, email attachments, Kubernetes Secrets, HTTP Basic auth headers, binary fields in JSON. Output is about 33% larger than the input.
• Base64URL — the same idea with - and _ instead of + and /, and usually no = padding, so it is safe in URLs, cookies and file names. JWT segments use it.
• URL (percent) encoding — for putting arbitrary text into a URL query parameter or path segment. It escapes reserved characters such as &, =, ?, /, # and spaces so they aren't mistaken for URL syntax.
• JSON escaping — for embedding a block of text (a log message, an HTML snippet, a nested JSON document) as a string value inside JSON, where quotes, backslashes and newlines must be escaped.

None of these are encryption. Anyone can decode Base64 or percent-encoding without a key, so never use them to hide passwords or tokens.

Common errors

• "Invalid Base64 string" — the input contains characters outside the alphabet, or it is Base64URL (-, _) being decoded as standard Base64. Switch to URL-safe mode, and remove any whitespace or data:…;base64, prefix.
• Garbled characters after decoding (é instead of é) — the bytes were decoded with the wrong character set. This tool decodes as UTF-8; if the original was Latin-1 or Windows-1252, it was encoded incorrectly at the source.
• URIError: URI malformed — a % is not followed by two hex digits, or the sequence isn't valid UTF-8. A literal percent sign must be encoded as %25.
• + turned into a space — in HTML form encoding (application/x-www-form-urlencoded), + means space. This tool uses encodeURIComponent, which encodes spaces as %20 and + as %2B, so values survive both conventions.
• Double-encoded URLs (%2520) — the value was encoded twice; %25 is an encoded %. Decode once more, then fix the code that encodes twice.

Encoding in code

// JavaScript (Unicode-safe Base64)
const b64 = btoa(String.fromCharCode(...new TextEncoder().encode("café")));
const url = encodeURIComponent("a&b=c");      // "a%26b%3Dc"
const esc = JSON.stringify("line 1\nline 2");  // → "line 1\nline 2" (quotes added, newline escaped)

# Python
import base64, urllib.parse, json
base64.b64encode("café".encode()).decode()
urllib.parse.quote("a&b=c", safe="")
json.dumps("line 1\nline 2")

For a deeper explanation of how Base64 works, padding, and the btoa() Unicode trap, read Base64 encoding explained.

Frequently asked questions

Further reading

• Base64 Encoding Explained: How It Works and When to Use ItHow Base64 turns bytes into text, why output is a third larger, what the = padding means, Base64 vs Base64URL, and how to handle Unicode correctly in JavaScript.

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