URL Encoder & Decoder - Free Online Tool
by Testsigma

Explanation

URL encoding (a.k.a. percent-encoding) is the process of converting characters that either are outside the unreserved ASCII set (like non-ASCII letters) or have special meaning in a URL (like ′′&′′, ′′?′′, ′′/′′) into a format that can be safely transmitted over the web.

Why it′s needed

• URLs must use the ASCII character‐set.
• Reserved characters in URLs (e.g., ′′?′′, ′′=′′, ′′&′′) may have structural meaning – if they appear as data, they can break parsing or lead to security issues.
• Non-ASCII characters (for example in internationalised domain names or query parameters) must be encoded so browsers, servers and proxies can handle them reliably.

How it works – step-by-step

1. String is converted to bytes using a character encoding (typically UTF-8).
2. Each byte that is not in the ′′safe/unreserved′′ set is replaced by a percent sign ′′%′′ plus the two-digit hexadecimal value of the byte. For example ′′ç′′ in UTF-8 becomes ′′%C3%A7′′.
3. The encoded string can then be appended into a URL path, query or form submission without breaking the structure.

Real-world simple example

′′François & Co′′ → ′′Fran%C3%A7ois%20%26%20Co′′ (space becomes %20, ampersand becomes %26, ′′ç′′ becomes two bytes).

Common use-cases

• Embedding user input into URL query parameters (e.g., ?search=…). If you include raw spaces or special characters, you risk malformed URLs or unintended parsing.
• Encoding path segments (e.g., background image filenames, internationalised content).
• Encoding values for application/x-www-form-urlencoded forms (i.e., HTML form submissions).
• Preparing links or redirects in marketing tools or email templates – safe links avoid broken UTM parameters.
• API requests: many APIs expect proper percent-encoded values in path/query parameters.

Why you can′t skip it

Failing to encode may lead to:

• Broken links (spaces, special characters causing 404s)
• Incorrect parameter parsing or injection risks (unescaped ′′&′′ splitting prematurely)
• International characters mis-interpreted or corrupted by browsers/servers. As one StackOverflow user remarked:
  ′′How can a failure to use urlencode be exploited?... What kind of bugs or failures can crop up with unencoded urls?′′

Where encoding is not needed (or should be used differently)

• Reserved URL syntax characters you intend to serve (for example, ′′/′′ separating path segments) should generally not be encoded if they are genuine separators.
• Sometimes decoding is required when receiving encoded parameters, so you must know when to encode vs decode (see next section).
• On the server-side, frameworks often provide functions to handle encoding/decoding rather than manually building strings.

URL Encoding

• Takes a ′′normal′′ string (with spaces, non-ASCII, reserved characters) and converts it to the safe, percent-encoded form.
• Example: Hello World! → Hello%20World%21

URL Decoding

• Reverse process: takes a percent-encoded string and returns the original form.
• Example: Fran%C3%A7ois%20Co → François Co
• Essential when reading query strings or path parameters that have been encoded.

Practical note for tools

Our tool provides both ′′Encode′′ and ′′Decode′′ modes, so you can switch freely depending on your workflow: encoding before sending, decoding when analysing or debugging links.

Key features

• Free and instant: No signup required, just paste input and get output immediately.
• UTF-8 by default: Ensures correct encoding of international characters.
• Encode / Decode toggle: Switch modes easily depending on your need (query parameter vs analysis).
• Live output copy: Click to copy encoded or decoded result – optimised for productivity.
• Safe for testing & QA workflows: Built by Testsigma (a trusted test-automation brand) so you can rely on accuracy and performance.

Why it matters

Having a reliable, browser-based encoder/decoder ensures you don′t introduce encoding errors in your workflows – whether you′re a QA engineer validating links, a marketer building UTM parameters, or a developer passing path/query segments in APIs.

How to use it (step-by-step)

1. Paste your string (for encoding) or paste your percent-encoded string (for decoding).
2. Select the mode: Encode or Decode.
3. Click ′′Convert′′ (or active auto-conversion) and view the result.
4. Use the ′′Copy′′ button to grab the result and use in your URL/parameter.

Tips for power users

• If you have long lists of parameters, use the tool in bulk mode (multiple lines) to encode/decode faster.
• Pay attention to plus (+) vs percent-encoding differences – some languages convert space to ′′+′′ in form-encoded contexts. For strict URLs, prefer %20. For example in Java the behaviour differs.
• When embedding into HTML contexts, remember to encode accordingly; sometimes you′ll need both HTML-entity encoding and URL encoding (e.g., when injecting into <a href> values).

Relevant standards and functions

The key standard for URI encoding is RFC 3986 – it defines the reserved and unreserved characters and the mechanics of percent-encoding.

In JavaScript:

• encodeURI() encodes a full URI (but leaves URL-syntax characters like ;, /, ?, # intact).
• encodeURIComponent() encodes query-string or path component values (more aggressive).

In server languages:

• Java: java.net.URLEncoder.encode(String, ′′UTF-8′′) (legacy method with caveats).
• In other languages like Python: urllib.parse.quote() or quote_plus().

Character encoding (UTF-8) matters

Using UTF-8 ensures consistent multi-byte behaviour and avoids character corruption. The tool and most modern web frameworks assume UTF-8.

Unreserved vs reserved characters

• Unreserved characters: A–Z a–z 0–9 - _ . ~ – these do not need encoding.
• Reserved characters: ! * ′ ( ) ; : @ & = + $ , / ? # [ ] – may require encoding depending on context.

Common pitfalls

• Using + to represent space vs %20: Some tools/frameworks treat them differently (e.g., HTML forms vs URLs) so it′s important to pick the correct encoding style. See the Java example.
• Failing to encode non-ASCII characters → broken links or mis-interpreted URLs.
• Double-encoding (encoding an already encoded string) → %25 showing up in URLs.

Best practices

• Always encode query parameter values and path segments when they contain spaces, special characters or non-ASCII characters.
• For static parts of a URL (known safe characters) you don′t need to encode, but if in doubt encode.
• Use UTF-8 encoding consistently across your application and tools.
• Avoid manual concatenation of URL strings without encoding – use libraries or built-in functions where possible.
• When decoding strings (e.g., from logs or analytics) always verify that the original string was correctly encoded, to avoid incorrect interpretation.

QA checklist

• Does the URL contain spaces or special characters (&, = etc.) in parameters? If yes, they should be encoded.
• After encoding, does the resulting URL still behave correctly in browsers, CLI tools or API clients?
• Reverse-decode the encoded output and confirm it yields the original string (round-trip test).
• Confirm that path segments and query parameters are treated correctly by your backend systems (e.g., escaped characters don′t break routing).
• Check performance: large batches of strings should encode/decode in an acceptable time.
• In analytics (link tracking, UTM parameters): verify that encoded links don′t inadvertently appear as broken in reports/logs.

Common mistakes to avoid

• Treating + as space in contexts where %20 is expected (these can differ across languages).
• Failing to decode when processing incoming parameter values – expect encoded strings from user input or URLs.
• Assuming encoding isn′t necessary because ′′my link works in browser′′ – sometimes it works now but fails on certain devices or international locales.

For developers

• Use language-specific libraries or functions (e.g., Java′s URLEncoder, Python′s urllib.parse.quote) rather than hand-coding your own logic. Example: Java: URLEncoder.encode(′′string′′, ′′UTF-8′′).
• When building APIs, ensure path and query parameter values are encoded before embedding them in the URL.
• In front-end JavaScript, use encodeURIComponent() for dynamic parameter values.

For QA/test engineers

• Use our Testsigma tool to validate that URLs generated by your app don′t contain unencoded characters that might break under load or internationalisation.
• Automate tests: for links you expect your app to generate, run encode → link usage → decode → verify the original value matches.
• Monitor analytics: track whether you have malformed links (404s or parameter drop-outs) and inspect whether improper encoding is the cause.

For marketers/UTM tracking

• When constructing UTM or affiliate links, encode any parameter value that contains spaces, special characters or user data (e.g., campaign=Summer Sale & Promo → campaign = Summer%20Sale%20%26%20Promo).
• Use encoded links in email templates or social posts to avoid truncation or broken links due to special characters.
• In reports and dashboards, recognise that encoded links will appear differently; decode when you′re reviewing raw data to get human-readable values.