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URL Encode Checker

Encode, decode, and verify URL percent-encoding (RFC 3986). Switch between encodeURIComponent (best for query values) and encodeURI (full URLs), and optionally treat + as space for form-style encoding.

Category: Developer · URL: /tools/url-encode-checker.html
Tip: For query strings, encode each key/value with “Component”, then join with &.
When encoding, spaces become +. When decoding, + becomes a space.
Diagnostics will show here after Encode/Decode/Check.
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Privacy: runs locally in your browser. No uploads, no tracking scripts.

How to use

Use this tool to encode/decode and quickly spot encoding problems.

  1. Paste text into the input box.
  2. Select Component for query values or Full URL for complete URLs.
  3. Optionally enable Treat + as space if your input/output is form-encoded.
  4. Click Encode, Decode, or Check to validate percent-encoding and see diagnostics.
Keywords this page targets (natural cluster): url encode checker, url encoder decoder, percent encoding checker, url decode checker, encodeURIComponent online, encodeURI online, decodeURIComponent online, query string encode tool, application/x-www-form-urlencoded encoder, plus to space decoder, url encoding validator, check malformed percent encoding, url escape characters, encode spaces in url, decode %2F %3F %26, url encode special characters, validate url encoded string, url encode online, url decode online
Secondary intents covered: Encode a query parameter value safely for APIs and redirects, Decode an encoded URL or query string to readable text, Validate whether a string has malformed % sequences, Convert spaces to %20 or to + for form submissions, Debug why a URL breaks due to double-encoding, Ensure reserved characters are handled correctly for full URLs vs components, Copy encoded/decoded output quickly for use in code, Normalize mixed input containing both %XX and +

FAQ

What’s the difference between encodeURIComponent and encodeURI?

encodeURIComponent encodes reserved characters and is best for individual query values; encodeURI keeps URL structure characters like :/?&=# for full URLs.

Why does + sometimes mean a space?

In application/x-www-form-urlencoded (HTML forms), spaces are often encoded as +; in general URL percent-encoding, spaces are usually %20.

How do I know if my string is valid URL-encoded?

Every % must be followed by exactly two hex digits (0-9, A-F). The Check button highlights the first invalid escape.

Why does decodeURIComponent fail sometimes?

It throws an error when the input has malformed percent escapes (like %2G) or incomplete sequences (like a trailing %).

Is it safe to encode an entire URL with encodeURIComponent?

Usually no—encoding a full URL will also encode : and /, which changes the URL. Use encodeURI for a full URL and encodeURIComponent for parts.

How can I avoid double-encoding?

Only encode raw text once; if you receive an already-encoded value, decode it first, then re-encode in the correct mode.

Does this tool send my input to a server?

No. The encoding/decoding and checks run locally in your browser.