Loading page
About this tool
Encode and decode URLs instantly for safe web usage.
The URL Encoder and Decoder runs three modes over whatever you paste. Encode calls JavaScript's built-in encodeURIComponent, which percent-escapes everything except A–Z, a–z, 0–9 and - _ . ! ~ * ' ( ) — so a space becomes %20, an ampersand %26 and a slash %2F. Decode calls decodeURIComponent to reverse it. Query JSON parses the input with the browser's URL and URLSearchParams API and prints every parameter as 2-space-indented JSON, while a table underneath lists each key, its decoded value and its encoded form. All three run on browser built-ins on your own device; no URL you paste is ever sent to a server.
Open URL Encoder Decoder Tool on AltFTool — it loads instantly in your browser.
Paste the URL, encoded text or query string into the input box. The Sample button loads a test URL containing spaces and an ampersand if you want something to try first.
Pick a mode: Encode percent-escapes the text, Decode turns %20 and %26 back into readable characters, and Query JSON lists every parameter as indented JSON. Output updates as you type.
Copy the result, download it as altftool-url-output.txt, or press Use output to send it back into the input and flip between encode and decode for a round-trip check.
Encode mode uses encodeURIComponent, which escapes : / ? & = # along with spaces — the encoding a value needs before it can sit safely inside a query parameter.
Query JSON returns the whole query string as indented JSON, and the table below it breaks out every parameter into key, decoded value and encoded value with a live parameter count.
Use output pushes the result back into the input box and flips encode to decode, so you can confirm a string survives the trip unchanged. Copy and a .txt download are one click away.
Encoding, decoding and query parsing all run on browser built-ins — encodeURIComponent, decodeURIComponent and the URL API. No upload, no server call, no stored history.
Paste the text into the input box and choose Encode. The tool runs encodeURIComponent on it, so https://example.com/a b comes back as https%3A%2F%2Fexample.com%2Fa%20b. Copy the result, download it as a .txt file, or hit Use output to feed it straight back in for a decode check.
%20 is a space. Percent-encoding writes a character as % followed by its byte value in hexadecimal, and the space character is 0x20. Paste any string with %20 into Decode mode and you get the readable text back — %26 is &, %3F is ?, %2F is /.
Because Encode mode uses encodeURIComponent, which is designed for a single value inside a URL rather than a complete address, and it treats : and / as characters that need escaping. That output is correct when you're embedding one URL inside another — a redirect_uri or a ?url= parameter. If you only want the parameter value escaped, paste just that value instead of the full address.
Decode mode shows "Input could not be processed for this mode" when the string contains a % that isn't followed by two valid hex digits — decodeURIComponent throws a URIError on sequences like 100% off or a truncated %E2%. A literal percent sign has to be written as %25 before it can be decoded.
Switch to Query JSON. Anything containing a ? is parsed as a full URL; a bare string like utm_source=news&utm_medium=email is parsed as a query string on its own. You get 2-space-indented JSON of every key and value, and the inspector table below shows the same parameters with their re-encoded values. Note that the JSON keeps only the last occurrence of a repeated key, while the table lists every one.
It depends on the mode, and this catches people out. Query JSON uses URLSearchParams, which follows form-encoding rules and reads + as a space. Decode mode uses decodeURIComponent, which leaves + exactly as it is. If a value looks wrong in Decode, try it in Query JSON.
Everything except the 71 characters encodeURIComponent leaves alone: A–Z, a–z, 0–9 and - _ . ! ~ * ' ( ). Anything else becomes one or more %XX pairs based on its UTF-8 bytes, so é encodes to %C3%A9 and an emoji expands to four pairs. Character counts for both the input and the output are shown above each box.
It's free with no signup, and nothing is uploaded. Every mode runs in your browser on native JavaScript functions — encodeURIComponent, decodeURIComponent and the URL API — with no network requests in the tool at all. The download button builds the .txt file locally from a Blob, so even that stays on your device.