diff --git a/Escape.php b/Escape.php
new file mode 100644
index 0000000..346e9d5
--- /dev/null
+++ b/Escape.php
@@ -0,0 +1,218 @@
+<?php declare(strict_types=1);
+
+/**
+ * A PHP implementation of OWASP Cross Site Scripting Prevention Cheat Sheet
+ *
+ * @package thisispiers\Xss
+ * @url https://github.com/thisispiers/xss-escape
+ * @see https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html
+ * Last retrieved: 2021-11-04
+ */
+
+namespace thisispiers\Xss;
+
+class Escape
+{
+    public static function encode(
+        mixed $untrusted_data,
+        string $format
+    ): string {
+        if (!is_string($untrusted_data)) {
+            $untrusted_data = strval($untrusted_data);
+        }
+        $encoded_data = '';
+        $untrusted_data_length = mb_strlen($untrusted_data, 'UTF-8');
+        for ($i = 0; $i < $untrusted_data_length; $i++) {
+            $char = mb_substr($untrusted_data, $i, 1, 'UTF-8');
+            $ord = mb_ord($char);
+            if (
+                $ord >= 256
+                || ($ord >= 48 && $ord <= 57)
+                || ($ord >= 65 && $ord <= 90)
+                || ($ord >= 97 && $ord <= 122)
+            ) {
+                $encoded_data .= $char;
+            } else {
+                $hex = mb_strtoupper(dechex($ord));
+                if ($format === 'html') {
+                    $encoded_data .= '&#x' . $hex . ';';
+                } else if ($format === 'unicode') {
+                    $encoded_data .= '\\u' . $ord;
+                } else if ($format === 'css') {
+                    $hex = str_pad($hex, 6, '0', \STR_PAD_LEFT);
+                    $encoded_data .= '\\' . $hex;
+                } else if ($format === 'url') {
+                    $encoded_data .= '%' . $hex;
+                }
+            }
+        }
+
+        return $encoded_data;
+    }
+
+    /**
+     * Context: Text in HTML body
+     * e.g. <span>UNTRUSTED DATA</span>
+     *
+     * Encode entities:
+     *     & to &amp;
+     *     < to &lt;
+     *     > to &gt;
+     *     " to &quot;
+     *     ' to &#x27;
+     */
+    public static function htmlBody(mixed $untrusted_data): string
+    {
+        if (!is_string($untrusted_data)) {
+            $untrusted_data = strval($untrusted_data);
+        }
+        $untrusted_data = str_replace('&', '&amp;',  $untrusted_data);
+        $untrusted_data = str_replace('<', '&lt;',   $untrusted_data);
+        $untrusted_data = str_replace('>', '&gt;',   $untrusted_data);
+        $untrusted_data = str_replace('"', '&quot;', $untrusted_data);
+        $untrusted_data = str_replace("'", '&#x27;', $untrusted_data);
+
+        return $untrusted_data;
+    }
+
+    /**
+     * Context: HTML in HTML body
+     * e.g. <div>UNTRUSTED HTML</div>
+     *
+     * HTML Validation (i.e. PHP HTML Purifier)
+     */
+    /*public static function validate_html($untrusted_html)
+    {
+
+    }*/
+
+    /**
+     * Context: Safe HTML attributes
+     * e.g. <input type="text" name="field_name" value="UNTRUSTED DATA">
+     *
+     * Limit to whitelisted attributes:
+     *     align, alink, alt, bgcolor, border, cellpadding, cellspacing, class,
+     *     color, cols, colspan, coords, dir, face, height, hspace, ismap, lang,
+     *     marginheight, marginwidth, multiple, nohref, noresize, noshade,
+     *     nowrap, ref, rel, rev, rows, rowspan, scrolling, shape, span, summary,
+     *     tabindex, title, usemap, valign, value, vlink, vspace, width.
+     *
+     * Except for alphanumeric characters, escape all characters with the
+     * &#xHH; HTML entity format, including spaces
+     *
+     * Apply additional validation to href and src attributes
+     */
+    public const HTML_ATTR_WHITELIST = [
+        'align', 'alink', 'alt', 'bgcolor', 'border', 'cellpadding',
+        'cellspacing', 'class', 'color', 'cols', 'colspan', 'coords', 'dir',
+        'face', 'height', 'hspace', 'ismap', 'lang', 'marginheight',
+        'marginwidth', 'multiple', 'nohref', 'noresize', 'noshade', 'nowrap',
+        'ref', 'rel', 'rev', 'rows', 'rowspan', 'scrolling', 'shape', 'span',
+        'summary', 'tabindex', 'title', 'usemap', 'valign', 'value', 'vlink',
+        'vspace', 'width',
+
+        'href', 'src',
+    ];
+    public static function htmlAttr(
+        string $attr,
+        mixed $untrusted_data,
+        bool $wrap = true
+    ): string {
+        $attr = mb_strtolower($attr);
+        if (!in_array($attr, static::HTML_ATTR_WHITELIST, true)) {
+            throw new \InvalidArgumentException('HTML attribute is not whitelisted');
+        }
+        if ($attr === 'href' || $attr === 'src') {
+            $validated = static::validateUrl($untrusted_data);
+        }
+
+        $encoded_data = static::encode($untrusted_data, 'html');
+        return $wrap ? ' ' . $attr . '="' . $encoded_data . '"' : $encoded_data;
+    }
+
+    /**
+     * Context: Untrusted URL in a `src` or `href` attribute
+     * e.g. <iframe src="UNTRUSTED URL" />
+     * e.g. <a href="UNTRUSTED URL">link</a>
+     *
+     * Whitelist https URLs only
+     *
+     * Apply additional whitelisting, canonicalization and anti-virus checks
+     * depending on the use-case
+     */
+    public static function validateUrl(mixed $untrusted_data): bool
+    {
+        if (!is_string($untrusted_data)) {
+            $untrusted_data = strval($untrusted_data);
+        }
+        $protocol = mb_substr($untrusted_data, 0, 8);
+        if ($protocol !== 'https://') {
+            throw new \InvalidArgumentException('URL is not HTTPS');
+        }
+
+        return true;
+    }
+
+    /**
+     * Context: JavaScript variable
+     * e.g. <script>var someValue='UNTRUSTED DATA';</script>
+     * e.g. <script>someFunction('UNTRUSTED DATA');</script>
+     *
+     * Do not use this when outputting JSON in HTML. Instead, use the dedicated
+     * jsonInHtml method
+     *
+     * Ensure JavaScript variables are quoted
+     *
+     * Except for alphanumeric characters, escape all characters with the
+     * \uXXXX unicode escaping format
+     *
+     * Avoid backslash encoding
+     */
+    public static function jsVar(mixed $untrusted_data): string
+    {
+        $encoded_data = static::encode($untrusted_data, 'unicode');
+        return $encoded_data;
+    }
+
+    /**
+     * Context: CSS value
+     * e.g. <div style="width: UNTRUSTED DATA;">
+     *
+     * CSS escaping supports \XX and \XXXXXX. Zero-pad to 6 characters
+     */
+    public static function cssValue(mixed $untrusted_data): string
+    {
+        $encoded_data = static::encode($untrusted_data, 'css');
+        return $encoded_data;
+    }
+
+    /**
+     * Context: URL parameter
+     * e.g. <a href="/site/search?value=UNTRUSTED DATA">link</a>
+     *
+     * Except for alphanumeric characters, escape all characters with the
+     * %HH escaping format
+     */
+    public static function urlParam(mixed $untrusted_data): string
+    {
+        $encoded_data = static::encode($untrusted_data, 'url');
+        return $encoded_data;
+    }
+
+    /**
+     * Context: JSON in HTML
+     * e.g. <div id="data" style="display:none"><?php echo \thisispiers\Xss\Escape::jsonInHtml($untrusted_data); ?></div>
+     * e.g. var data = JSON.parse(document.getElementById('data').textContent);
+     *
+     * Encode entities: & < > " '
+     *
+     * Output JSON inside a hidden element before calling JSON.parse(el.textContent)
+     *
+     * @param mixed $untrusted_data
+     */
+    public static function jsonInHtml(mixed $untrusted_data): string
+    {
+        $flags = \JSON_HEX_AMP|\JSON_HEX_TAG|\JSON_HEX_QUOT|\JSON_HEX_APOS|\JSON_THROW_ON_ERROR;
+        return json_encode($untrusted_data, $flags) ?: '[]';
+    }
+}
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..0a04128
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,165 @@
+                   GNU LESSER GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+
+  This version of the GNU Lesser General Public License incorporates
+the terms and conditions of version 3 of the GNU General Public
+License, supplemented by the additional permissions listed below.
+
+  0. Additional Definitions.
+
+  As used herein, "this License" refers to version 3 of the GNU Lesser
+General Public License, and the "GNU GPL" refers to version 3 of the GNU
+General Public License.
+
+  "The Library" refers to a covered work governed by this License,
+other than an Application or a Combined Work as defined below.
+
+  An "Application" is any work that makes use of an interface provided
+by the Library, but which is not otherwise based on the Library.
+Defining a subclass of a class defined by the Library is deemed a mode
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+
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+Application with the Library.  The particular version of the Library
+with which the Combined Work was made is also called the "Linked
+Version".
+
+  The "Minimal Corresponding Source" for a Combined Work means the
+Corresponding Source for the Combined Work, excluding any source code
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+based on the Application, and not on the Linked Version.
+
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+and utility programs needed for reproducing the Combined Work from the
+Application, but excluding the System Libraries of the Combined Work.
+
+  1. Exception to Section 3 of the GNU GPL.
+
+  You may convey a covered work under sections 3 and 4 of this License
+without being bound by section 3 of the GNU GPL.
+
+  2. Conveying Modified Versions.
+
+  If you modify a copy of the Library, and, in your modifications, a
+facility refers to a function or data to be supplied by an Application
+that uses the facility (other than as an argument passed when the
+facility is invoked), then you may convey a copy of the modified
+version:
+
+   a) under this License, provided that you make a good faith effort to
+   ensure that, in the event an Application does not supply the
+   function or data, the facility still operates, and performs
+   whatever part of its purpose remains meaningful, or
+
+   b) under the GNU GPL, with none of the additional permissions of
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+
+  3. Object Code Incorporating Material from Library Header Files.
+
+  The object code form of an Application may incorporate material from
+a header file that is part of the Library.  You may convey such object
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+layouts and accessors, or small macros, inline functions and templates
+(ten or fewer lines in length), you do both of the following:
+
+   a) Give prominent notice with each copy of the object code that the
+   Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the object code with a copy of the GNU GPL and this license
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+  4. Combined Works.
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+  You may convey a Combined Work under terms of your choice that,
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+portions of the Library contained in the Combined Work and reverse
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+   a) Give prominent notice with each copy of the Combined Work that
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+   b) Accompany the Combined Work with a copy of the GNU GPL and this license
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+   c) For a Combined Work that displays copyright notices during
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+
+   e) Provide Installation Information, but only if you would otherwise
+   be required to provide such information under section 6 of the
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+   Combined Work produced by recombining or relinking the
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+facilities that are not Applications and are not covered by this
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diff --git a/README.md b/README.md
new file mode 100644
index 0000000..9900874
--- /dev/null
+++ b/README.md
@@ -0,0 +1,150 @@
+# \thisispiers\Xss\Escape
+
+A PHP implementation of [OWASP's Cross Site Scripting Prevention Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html)
+
+Released under LGPL v3.0. Requires PHP >= 7.1 and mbstring extension
+
+Install with Composer `composer require thisispiers/xss-escape`
+
+## Usage
+
+Untrusted data should be encoded differently depending on context. This library provides a static method for each context.
+
+### Text in HTML Body
+
+i.e. `<span>UNTRUSTED DATA</span>`
+
+```
+htmlBody(mixed $untrusted_data): string
+```
+
+`$untrusted_data` is cast to string
+
+### HTML in HTML body
+
+i.e. `<div>UNTRUSTED HTML</div>`
+
+Use a full HTML validator in this context, such as [HTML Purifier](https://github.com/ezyang/htmlpurifier) or [DOMPurify](https://github.com/cure53/DOMPurify)
+
+### Safe HTML attributes
+
+i.e. `<input type="text" name="field_name" value="UNTRUSTED DATA">`
+
+```
+htmlAttr(string $attr, mixed $untrusted_data, bool $wrap = true): string
+```
+
+`$attr` must be one of
+- align
+- alink
+- alt
+- bgcolor
+- border
+- cellpadding
+- cellspacing
+- class
+- color
+- cols
+- colspan
+- coords
+- dir
+- face
+- height
+- href (see [URLs](#URLs))
+- hspace
+- ismap
+- lang
+- marginheight
+- marginwidth
+- multiple
+- nohref
+- noresize
+- noshade
+- nowrap
+- ref
+- rel
+- rev
+- rows
+- rowspan
+- scrolling
+- shape
+- span
+- src (see [URLs](#URLs))
+- summary
+- tabindex
+- title
+- usemap
+- valign
+- value
+- vlink
+- vspace
+- width
+
+`$untrusted_data` is cast to string
+
+If `$wrap` is `true`, the returned string is prefixed by a space, the attribute name, an equal sign and wrapped in double quote marks i.e. `` value="ENCODED DATA"``.
+
+### URLs
+
+URLs in `src` or `href` HTML attributes i.e. `<iframe src="UNTRUSTED URL" />` or `<a href="UNTRUSTED URL">link</a>`
+
+```
+validateUrl(mixed $untrusted_data): bool
+```
+
+`$untrusted_data` is cast to string
+
+Untrusted URLs are currently only checked to be HTTPS. This is a crude check to avoid becoming a full URL parsing library. It is highly recommended that you run more sophisticated validation on your untrusted URLs, such as rejecting URLs by hostname.
+
+### JavaScript variables
+
+i.e. `<script>var someValue='UNTRUSTED DATA';</script>` or `<script>someFunction('UNTRUSTED DATA');</script>`
+
+```
+jsVar(mixed $untrusted_data): string
+```
+
+`$untrusted_data` is cast to string
+
+### CSS values
+
+i.e. `<div style="width: UNTRUSTED DATA;">`
+
+```
+cssValue(mixed $untrusted_data): string
+```
+
+`$untrusted_data` is cast to string
+
+### URL parameters
+
+i.e. `<a href="/site/search?value=UNTRUSTED DATA">link</a>`
+
+```
+urlParam(mixed $untrusted_data): string
+```
+
+`$untrusted_data` is cast to string
+
+### JSON in HTML
+
+```
+jsonInHtml(mixed $untrusted_data): string
+```
+
+`$untrusted_data` is cast to string
+
+Output JSON inside a hidden element before calling `JSON.parse` e.g.
+```
+<div id="data" style="display:none"><?php echo \thisispiers\Xss\Escape::jsonInHtml($untrusted_data); ?></div>
+<script>var data = JSON.parse(document.getElementById('data').textContent);</script>
+```
+
+## Contributing & Help
+
+Don't expect frequent updates, but pull requests for security and performance improvements are welcome!
+
+There is no guarantee this library complies with the latest OWASP cheat sheet recommendations. Create an issue if you think it's out of date, or start a pull request.
+
+To save keystrokes, you might want to create an alias for this class
+e.g. `class_alias('\\thisispiers\Xss\\Escape', '\\esc');`
\ No newline at end of file
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..3d37014
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,14 @@
+{
+    "name": "thisispiers/xss-escape",
+    "description": "A PHP implementation of OWASP Cross Site Scripting Prevention Cheat Sheet",
+    "license": "LGPL-3.0-only",
+    "require": {
+        "php": ">=7.1",
+        "ext-mbstring": "*"
+    },
+    "autoload": {
+        "psr-4": {
+            "thisispiers\\Xss\\": ""
+        }
+    }
+}
\ No newline at end of file