My decoded output shows syntax errors: the JSON looks broken. Why?

This usually happens when the string was encoded more than once (double-encoded). If the server or client called encodeURIComponent twice, the first decoding step produces another encoded string (e.g. %2522 → %22 → "). Run the tool a second time on the output to decode the second layer. Look for %25 in the string: %25 is the encoding of %, which only appears if encoding was applied to an already-encoded string.

The URL contains + signs: why does my decoded JSON show spaces or literal + symbols?

There are two conventions for encoding spaces in URLs: %20 (RFC 3986, used by encodeURIComponent) and + (HTML form encoding, application/x-www-form-urlencoded). If the original encoder used + for spaces, decodeURIComponent will leave the + as a literal + character rather than a space. If your decoded JSON shows unexpected + symbols, first replace all + with %20 before decoding, or use a form-encoded decoder.

I copied a URL from the browser address bar and the encoding looks different from what DevTools shows: why?

Browsers display URLs in the address bar with minimal encoding for readability: they often show some characters unencoded even though they are technically encoded in the actual HTTP request. The DevTools Network tab shows the raw, fully-encoded URL as sent to the server. For reliable decoding, copy the parameter value from DevTools → Network → Headers → Query String Parameters, not from the address bar.

How do I extract just the JSON part from a full URL to paste here?

In browser DevTools: Network tab → click the request → Headers → scroll to Query String Parameters → find your JSON parameter and copy its value (right-click → Copy value). In curl output, look for the parameter after ? or & and copy the value after =. You only need the encoded value, not the full URL or the parameter name.

Can I decode a full URL: not just the query parameter value?

Pasting a full URL will decode every %XX sequence in it, which affects the path, domain, and all parameters at once. If you want to decode just the JSON parameter, extract and paste only that parameter's value. If you paste the full URL, the output will be the full URL with percent-sequences decoded: not a JSON object.

My decoded JSON looks correct but I get SyntaxError when I parse it in JavaScript: what is wrong?

Two common causes: (1) the JSON contains escaped unicode sequences like \u0022 that need a second round of unescaping: this happens when JSON was serialized twice. (2) the string has invisible characters (null bytes, non-breaking spaces) from copy-paste. Check the JSON in this tool's output: it pretty-prints and validates the result. If the validator shows it as valid, the issue is in your runtime environment; try JSON.parse(decodeURIComponent(value)) instead of decoding separately.

Does this tool pretty-print the decoded JSON?

Yes. After percent-decoding, the result is parsed with JSON.parse and re-formatted with 2-space indentation. This makes it easy to read deeply nested objects. If the decoded string is not valid JSON, the raw decoded text is shown along with the parse error.

Is the decoded JSON sent to a server?

No. Decoding runs entirely in your browser using the native decodeURIComponent function: the same function used by all JavaScript environments. No data leaves your device. This is important when debugging URLs that contain API tokens, user IDs, or session data embedded in the JSON.

JSON Tools › JSON URL Decode

URL-encoded Input

Decoded JSON

Decoded JSON will appear here.

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JSON URL Decode Online

Paste a percent-encoded JSON string and decode it back to readable, pretty-printed JSON. Copies from browser DevTools, curl output, API access logs, and network requests are decoded in one click: no manual character replacement, no regex.

Where you actually encounter percent-encoded JSON

Percent-encoded JSON turns up in the places you are least prepared for it: in the middle of a curl debug session, in a browser network request you are trying to reproduce, in a mobile analytics event payload, or in a support ticket that contains a raw URL. Every time you see a query parameter starting with %7B (the encoding of {) or %5B (the encoding of [), that is JSON waiting to be decoded.

Concrete example

Encoded: from a URL query string or network log

%7B%22userId%22%3A%22u_8842%22%2C%22plan%22%3A%22pro%22%2C%22features%22%3A%5B%22export%22%2C%22api%22%5D%7D

Decoded: readable, formatted JSON

{
  "userId": "u_8842",
  "plan": "pro",
  "features": ["export", "api"]
}

Step-by-step: copying from browser DevTools

Open DevTools (F12 or Cmd+Option+I), go to the Network tab.
Reload the page or trigger the API call you want to inspect.
Click the request in the list. Go to Headers → scroll to Query String Parameters.
Find the JSON parameter (usually named filter, query, state, or similar). Right-click the value → Copy.
Paste into this tool and click Decode →.

Common decoding problems and what they mean

Decoded output contains %22 or %7B

The string was double-encoded: encoded twice. Run the tool again on the output to decode the second layer. Look for %25 in the input, which is an encoded %.

Decoded output has + instead of spaces

The original encoder used HTML form encoding (application/x-www-form-urlencoded) where + means space. Replace + with %20 before decoding: or use a form-encoded decoder.

SyntaxError after decoding

The decoded string is not valid JSON. This may mean the original JSON was malformed before encoding, or only part of the encoded value was copied. Use JSON Repair to fix minor issues.

URIError: malformed URI sequence

The percent-encoding is invalid: a % sign that is not followed by two hex digits, or an incomplete multibyte sequence. This occurs when part of the encoded value was truncated during copy.

Privacy

All decoding runs client-side using the browser's native decodeURIComponent function. No request is made to any external server. Open DevTools → Network while using this tool: you will see zero outbound requests. This matters when decoding URLs that include session tokens, user data, or internal API credentials embedded in filter parameters.

Frequently asked questions

My decoded JSON still shows percent-sequences: why is it double-encoded?

Double-encoding happens when encodeURIComponent is called on an already-encoded string. The first decode produces another encoded string. Run this tool a second time on the output. Look for %25 in the original: %25 is the encoding of %, which only appears if encoding was stacked.

The decoded output has + symbols where I expected spaces: what is happening?

Two URL encoding conventions exist: RFC 3986 (encodeURIComponent) encodes spaces as %20, and HTML form encoding (application/x-www-form-urlencoded) encodes spaces as +. If the original form used the form-encoding convention, replace all + with %20 before decoding here.

How do I extract the correct value to paste: from DevTools, not the address bar?

Browsers display URLs in the address bar with minimal encoding for readability. For reliable decoding, use DevTools → Network → click the request → Headers → Query String Parameters → right-click the value → Copy. This gives you the actual encoded string sent to the server.

I pasted the full URL including the domain. Will that work?

Pasting the full URL will decode all %XX sequences across the entire URL: path, domain, and all parameters simultaneously. The output will be the full URL with sequences decoded, not a clean JSON object. Extract just the parameter value (the part after = and before & ) for a clean result.

Does the tool validate the decoded JSON?

Yes. After decoding, the result is passed through JSON.parse. If it is valid JSON, the pretty-printed version is shown. If not, the raw decoded string is displayed with the parse error so you can diagnose whether the problem is in the encoding or the original JSON.

Can I decode JSONL (multiple JSON lines) from a URL?

Yes: if the encoded string contains newlines (encoded as %0A), the tool will decode them and show the multi-line result. JSONL in URL parameters is rare because of size limits, but the decoder handles it.

Is there a risk of the decoded JSON being sent to your server?

No. Decoding uses the browser's built-in decodeURIComponent function entirely locally. No network request is made. The JSON you decode never leaves your device.

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