Fix Malformed Percent-Encoding
See why decodeURIComponent throws on a trailing % or a lone %2, and how to clean the string before decoding.
Part of the free URL Decoder. Runs in your browser — nothing is uploaded.
Fix Malformed Percent-Encoding
JavaScript throws URIError: URI malformed when a % is not followed by two hex digits. That usually means a truncated log line, a copy-paste cut-off, or a literal percent that was never encoded as %25.
Worked example: A truncated value
Encoded
hello%2
Error
URIError: URI malformed %2 is not a complete %HH pair
Practical tip
Replace leftover % that are not %HH with %25, then decode. Or reject the input — a truncated token should not be trusted.
How to use this URL Decoder
- 1Use the live tool above — it runs entirely in your browser and never uploads your data.
- 2Paste the sample from the worked example, or use your own input.
- 3Copy the result, then adapt the same steps in your editor, script, or pipeline.
Fix Malformed Percent-Encoding FAQs
Why does decodeURIComponent throw?
A % is missing its two hex digits, or the resulting bytes are not valid UTF-8.
How do I decode safely in JavaScript?
try { decodeURIComponent(s) } catch { return s } — or show the error so the caller can fix the value.
More URL Decoder pages
- URL Decode %20 to SpacesDecode %20 and other percent-encoded bytes back to readable text. Paste an encoded URL or query value.
- Decode a Query String OnlineDecode a full query string and read every parameter. Turns %XX sequences back into readable values.
- decodeURIComponent OnlineRun decodeURIComponent on any string. Catch malformed % sequences and see the exact JavaScript result.
- Decode + as a SpaceTreat + as a space before percent-decoding, the same way HTML form bodies are decoded.
- Decode UTF-8 Percent-EncodingDecode percent-encoded UTF-8 back to accents, CJK characters and emoji. See caf%C3%A9 become café.
- Parse URL Query ParametersSplit a URL into protocol, host, path and a table of query parameters. Decode each value automatically.
- Bulk URL DecoderDecode many percent-encoded lines at once. Paste a list of values or URLs and decode each line.
- Decode a Nested Redirect URLDecode a return_to / redirect parameter that is itself a URL. See the real destination hidden behind percent-encoding.
- Decode + and % Sequences TogetherDecode strings that mix + (form space) and %HH sequences. The usual case for query strings from HTML forms.