URL Encoder / Decoder

Why use a URL encoder?

Percent-encoding (or URL encoding) is essential whenever you work with parameters in a URL. Special characters like &, =, ? or spaces must be encoded so they don't break the URL structure.

Without proper encoding, a parameter containing price=10&20 would be interpreted as two separate parameters (price=10 and 20). The browser can't guess your intent: encoding removes the ambiguity.

Three situations where URL encoding is essential:

• Query string parameters - An & or = in a value splits the string at the wrong place
• UTM parameters - Spaces or accented characters in utm_campaign break analytics tracking
• Redirects and callbacks - Nested URLs (OAuth, SSO, marketing emails) must be fully encoded

How to use the URL encoder / decoder in 3 steps

Step 1: Paste your content

Paste into the input area:

• Plain text if you want to encode (e.g. price=10€ & free shipping)
• An encoded string if you want to decode (e.g. price%3D10%E2%82%AC+%26+free+shipping)

Step 2: Select the operation

Click URL encode to transform text into percent-encoding, or URL decode to retrieve the original text from an encoded string.

Step 3: Copy the result

The result appears instantly. Click the copy button to grab the converted string, ready to be inserted into your code, URL or configuration.

What is percent-encoding?

Percent-encoding is the mechanism defined by RFC 3986 for representing special characters in a URI. Each disallowed byte is replaced by % followed by two hexadecimal digits representing its UTF-8 value.

Practical example:

Original text: Café & Thé = 15€
Encoded:       Caf%C3%A9+%26+Th%C3%A9+%3D+15%E2%82%AC

The é (U+00E9) takes two bytes in UTF-8 (C3 A9), hence %C3%A9. The € symbol (U+20AC) takes three bytes (E2 82 AC), hence %E2%82%AC.

Unreserved characters (never encoded)

These characters pass through unchanged in a URL:

A-Z  a-z  0-9  -  _  .  ~

Reserved characters (encoded in values)

Encoding table for common characters

Note: The only difference between query and path encoding is the space character. In a query string (application/x-www-form-urlencoded), the space becomes +. In a URL path, it becomes %20.

Real-world use cases

Case 1: UTM parameters with special characters

Problem: You're creating a tracking link for a campaign named "Summer sale 2025 - 50%".

Without encoding:

https://captaindns.com?utm_campaign=Summer sale 2025 - 50%

The spaces, dash and % break the link. Google Analytics can't capture the campaign.

With encoding:

https://captaindns.com?utm_campaign=Summer+sale+2025+%2D+50%25

Tracking works correctly, every special character is preserved.

Case 2: OAuth callback URL

Problem: You're setting up an OAuth flow and need to pass a return URL as a parameter.

Without encoding:

https://auth.captaindns.com/authorize?redirect_uri=https://captaindns.com/callback?token=abc&scope=read

The server interprets scope=read as a parameter of /authorize, not of /callback.

With redirect_uri encoding:

https://auth.captaindns.com/authorize?redirect_uri=https%3A%2F%2Fcaptaindns.com%2Fcallback%3Ftoken%3Dabc&scope=read

The nested URL is correctly isolated. The OAuth flow works as expected.

Case 3: Debugging a broken email link

Problem: A customer reports that a link in your newsletter doesn't work. The raw link in the email looks like:

https://captaindns.com/offre?nom=Caf%C3%A9+%26+Th%C3%A9&code=PROMO%2D20

Action: Paste the part after ? into the decoder to read the parameters:

• nom = Café & Thé
• code = PROMO-20

This lets you immediately identify whether the values are correct or if double encoding has corrupted the link.

❓ FAQ - Frequently asked questions

Q: What is the difference between URL encoding and Base64?

A: URL encoding (percent-encoding) replaces special characters with %XX to make them URL-safe. Base64 encodes binary data (images, files) into ASCII characters. The two are not interchangeable: use URL encoding for URL parameters, Base64 for transmitting binary data as text.

Q: Why do spaces become + signs?

A: This is a convention of the application/x-www-form-urlencoded format, used by HTML forms and query strings. In URL paths (before the ?), the space is encoded as %20. Both representations are valid in their respective contexts.

Q: Which characters are not encoded?

A: The 66 unreserved characters defined by RFC 3986 are never modified: letters A-Z, a-z, digits 0-9, and four symbols: -, _, ., ~. All other characters are encoded when they appear in a parameter value.

Q: Can I encode a full URL?

A: No, only encode the parameter values. Structural separators (://, /, ?, &, =) must remain as-is for the URL to stay functional. For example, encode the value Café & Thé but not the ? or & that structure the URL.

Q: What happens with double encoding?

A: Double encoding turns %26 into %2526 (the % itself gets re-encoded). The server then receives the literal string %26 instead of &. This is a common pitfall with nested redirects. If you suspect double encoding, decode twice and compare the results.

Q: What happens with invalid encoding?

A: If you try to decode an invalid sequence (e.g. %GG or a bare %), the tool displays an explanatory error message instead of a corrupted result. Fix the source sequence before trying again.

Complementary tools

Useful resources

• RFC 3986 – Uniform Resource Identifier (URI): Generic Syntax (official percent-encoding specification)
• RFC 3987 – Internationalized Resource Identifiers (IRIs) (extension of RFC 3986 for Unicode characters)
• MDN – encodeURIComponent() (JavaScript URL encoding reference)
• WHATWG URL Standard (living specification for URL parsing and serialization)