Skip to content
CalcLab

URL Encoder / Decoder

Percent-encode or decode URL text.
Encode
Component (encodeURIComponent)
No data
No results yet — Enter values and run the tool to see results.

What is this calculator?

Percent-encodes text for safe use in URLs, or decodes a percent-encoded string. It offers two scopes because they escape different character sets: component encoding for a single query value, and full-URI encoding for a whole address.

Use it when:

  • You are building a query string and a value contains spaces, ampersands, or slashes.
  • You need to read a percent-encoded URL from a log or a redirect.
  • You must decide whether to escape a whole URL or just one parameter within it.

Intended for: Web developers constructing or debugging URLs and query strings.

How is this calculated?

  1. The text is converted to UTF-8 bytes, and each byte that is not permitted unescaped is written as `%` followed by two hexadecimal digits.
  2. COMPONENT scope escapes aggressively, including the reserved characters `/`, `?`, `#`, `&`, `=`, and `:`. Use it for one query parameter value, where those characters would otherwise be read as structure.
  3. FULL URI scope leaves those reserved characters intact, because in a complete address they carry meaning. Use it for a whole URL you do not want to break.
  4. Decoding reverses the substitution, converting each `%XX` sequence back to its byte and then interpreting the result as UTF-8.

Example

Encoding `a b&c=d` as a single query parameter value (component scope).

  1. The space becomes `%20`.
  2. The `&` becomes `%26` and the `=` becomes `%3D`, so neither is read as query structure.

Result: `a%20b%26c%3Dd` — safe to place after `?q=` without breaking the query string.

Frequently asked questions

When should I use component scope rather than full URI?

Use component scope whenever you are encoding a VALUE that will sit inside a larger URL — a query parameter, a path segment. Use full URI only when escaping an entire address whose structural characters must survive.

Why is a space sometimes `%20` and sometimes `+`?

Percent-encoding uses `%20`. The `+` form belongs to the older `application/x-www-form-urlencoded` format used by HTML form submissions. This tool produces `%20`.

Why does decoding fail on some strings?

A malformed sequence — a `%` not followed by two valid hex digits, or bytes that do not form valid UTF-8 — cannot be decoded and is reported as an error rather than silently mangled.

Assumptions

What this calculator takes as given:

  • The transformation is performed in your browser; the text you paste is not uploaded or stored.
  • Input is treated as UTF-8 text.
  • Percent-encoding is applied over UTF-8 bytes, per current URL standards.

Limitations

What this calculator cannot know or does not model:

  • The `application/x-www-form-urlencoded` `+`-for-space convention is not produced or consumed.
  • Internationalised domain names (punycode) are not converted.
  • It does not validate that the result is a well-formed URL — only that the escaping is correct.

References

Related tools