diff --git a/src/core/operations/XMLBeautify.mjs b/src/core/operations/XMLBeautify.mjs
index 2cabb9b2..db2c6b64 100644
--- a/src/core/operations/XMLBeautify.mjs
+++ b/src/core/operations/XMLBeautify.mjs
@@ -4,9 +4,110 @@
  * @license Apache-2.0
  */
 
-import vkbeautify from "vkbeautify";
 import Operation from "../Operation.mjs";
 
+/**
+ * Adapted from vkBeautify (c) 2012 Vadim Kiryukhin, MIT/GPL dual licence.
+ */
+function createShiftArr(step) {
+    let space = "    ";
+
+    if (isNaN(parseInt(step, 10))) {
+        space = step;
+    } else {
+        switch (step) {
+            case 1: space = " "; break;
+            case 2: space = "  "; break;
+            case 3: space = "   "; break;
+            case 4: space = "    "; break;
+            case 5: space = "     "; break;
+            case 6: space = "      "; break;
+            case 7: space = "       "; break;
+            case 8: space = "        "; break;
+            case 9: space = "         "; break;
+            case 10: space = "          "; break;
+            case 11: space = "           "; break;
+            case 12: space = "            "; break;
+        }
+    }
+
+    const shift = ["\n"];
+    for (let ix = 0; ix < 100; ix++) {
+        shift.push(shift[ix] + space);
+    }
+    return shift;
+}
+
+/**
+ * Adapted from vkBeautify (c) 2012 Vadim Kiryukhin, MIT/GPL dual licence.
+ *
+ * Fix for issue #2501: the xmlns check is moved before the generic self-close
+ * check so that a fragment like `xmlns="foo" />` is caught here rather than
+ * by the `/>` branch. When such a fragment ends with `/>` the element is
+ * self-closing, so we decrement deep to undo the increment that fired when
+ * the preceding `<tagName` fragment was classified as an opening element.
+ */
+function xmlBeautify(text, step) {
+    const ar = text
+        .replace(/>\s{0,}</g, "><")
+        .replace(/</g, "~::~<")
+        .replace(/\s*xmlns:/g, "~::~xmlns:")
+        .replace(/\s*xmlns=/g, "~::~xmlns=")
+        .split("~::~");
+
+    const len = ar.length;
+    const shift = createShiftArr(step);
+    let inComment = false;
+    let deep = 0;
+    let str = "";
+
+    for (let ix = 0; ix < len; ix++) {
+        // start comment or <![CDATA[...]]> or <!DOCTYPE
+        if (ar[ix].search(/<!/) > -1) {
+            str += shift[deep] + ar[ix];
+            inComment = true;
+            if (ar[ix].search(/-->/) > -1 || ar[ix].search(/\]>/) > -1 || ar[ix].search(/!DOCTYPE/) > -1) {
+                inComment = false;
+            }
+        // end comment or <![CDATA[...]]>
+        } else if (ar[ix].search(/-->/) > -1 || ar[ix].search(/\]>/) > -1) {
+            str += ar[ix];
+            inComment = false;
+        // <elm></elm>
+        } else if (
+            /^<\w/.exec(ar[ix - 1]) && /^<\/\w/.exec(ar[ix]) &&
+            /^<[\w:\-.,]+/.exec(ar[ix - 1])?.[0] === /^<\/[\w:\-.,]+/.exec(ar[ix])?.[0].replace("/", "")
+        ) {
+            str += ar[ix];
+            if (!inComment) deep--;
+        // <elm>
+        } else if (ar[ix].search(/<\w/) > -1 && ar[ix].search(/<\//) === -1 && ar[ix].search(/\/>/) === -1) {
+            str = !inComment ? str + shift[deep++] + ar[ix] : str + ar[ix];
+        // <elm>...</elm>
+        } else if (ar[ix].search(/<\w/) > -1 && ar[ix].search(/<\//) > -1) {
+            str = !inComment ? str + shift[deep] + ar[ix] : str + ar[ix];
+        // </elm>
+        } else if (ar[ix].search(/<\//) > -1) {
+            str = !inComment ? str + shift[--deep] + ar[ix] : str + ar[ix];
+        // <? xml ... ?>
+        } else if (ar[ix].search(/<\?/) > -1) {
+            str += shift[deep] + ar[ix];
+        // xmlns: or xmlns= — must be checked before the generic /> branch so that a self-closing
+        // element with a namespace attribute (e.g. <b xmlns="foo" />) is handled here.
+        } else if (ar[ix].search(/xmlns:/) > -1 || ar[ix].search(/xmlns=/) > -1) {
+            str = !inComment ? str + shift[deep] + ar[ix] : str + ar[ix];
+            if (ar[ix].search(/\/>/) > -1) deep--;
+        // <elm/>
+        } else if (ar[ix].search(/\/>/) > -1) {
+            str = !inComment ? str + shift[deep] + ar[ix] : str + ar[ix];
+        } else {
+            str += ar[ix];
+        }
+    }
+
+    return str[0] === "\n" ? str.slice(1) : str;
+}
+
 /**
  * XML Beautify operation
  */
@@ -39,7 +140,7 @@ class XMLBeautify extends Operation {
      */
     run(input, args) {
         const indentStr = args[0];
-        return vkbeautify.xml(input, indentStr);
+        return xmlBeautify(input, indentStr);
     }
 
 }
diff --git a/tests/operations/tests/XMLBeautify.mjs b/tests/operations/tests/XMLBeautify.mjs
new file mode 100644
index 00000000..31624ba4
--- /dev/null
+++ b/tests/operations/tests/XMLBeautify.mjs
@@ -0,0 +1,59 @@
+/**
+ * XML Beautify tests.
+ *
+ * @author Allan Leary
+ * @copyright Crown Copyright 2026
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "XML Beautify: basic nested elements",
+        input: "<root><parent><child/></parent></root>",
+        expectedOutput: "<root>\n\t<parent>\n\t\t<child/>\n\t</parent>\n</root>",
+        recipeConfig: [{ op: "XML Beautify", args: ["\t"] }],
+    },
+    {
+        name: "XML Beautify: self-closing element without xmlns",
+        input: "<a><b/></a>",
+        expectedOutput: "<a>\n\t<b/>\n</a>",
+        recipeConfig: [{ op: "XML Beautify", args: ["\t"] }],
+    },
+    {
+        name: "XML Beautify: self-closing element with xmlns (issue #2501)",
+        input: "<a><b xmlns=\"foo\" /></a>",
+        expectedOutput: "<a>\n\t<b\n\t\txmlns=\"foo\" />\n</a>",
+        recipeConfig: [{ op: "XML Beautify", args: ["\t"] }],
+    },
+    {
+        name: "XML Beautify: self-closing element with multiple xmlns attributes (issue #2501)",
+        input: "<a><b xmlns:foo=\"a\" xmlns:bar=\"b\" /></a>",
+        expectedOutput: "<a>\n\t<b\n\t\txmlns:foo=\"a\"\n\t\txmlns:bar=\"b\" />\n</a>",
+        recipeConfig: [{ op: "XML Beautify", args: ["\t"] }],
+    },
+    {
+        name: "XML Beautify: xmlns on opening (non-self-closing) tag",
+        input: "<a><b xmlns=\"foo\">text</b></a>",
+        expectedOutput: "<a>\n\t<b\n\t\txmlns=\"foo\">text\n\t</b>\n</a>",
+        recipeConfig: [{ op: "XML Beautify", args: ["\t"] }],
+    },
+    {
+        name: "XML Beautify: siblings after xmlns self-closing are correctly indented",
+        input: "<root><a xmlns=\"foo\" /><b/><c/></root>",
+        expectedOutput: "<root>\n\t<a\n\t\txmlns=\"foo\" />\n\t<b/>\n\t<c/>\n</root>",
+        recipeConfig: [{ op: "XML Beautify", args: ["\t"] }],
+    },
+    {
+        name: "XML Beautify: xml declaration preserved",
+        input: "<?xml version=\"1.0\"?><root><child/></root>",
+        expectedOutput: "<?xml version=\"1.0\"?>\n<root>\n\t<child/>\n</root>",
+        recipeConfig: [{ op: "XML Beautify", args: ["\t"] }],
+    },
+    {
+        name: "XML Beautify: 4-space indent",
+        input: "<root><child/></root>",
+        expectedOutput: "<root>\n    <child/>\n</root>",
+        recipeConfig: [{ op: "XML Beautify", args: ["    "] }],
+    },
+]);