diff --git a/.github/workflows/api-verification.yml b/.github/workflows/api-verification.yml
index de7e967b24f..443adb471f3 100644
--- a/.github/workflows/api-verification.yml
+++ b/.github/workflows/api-verification.yml
@@ -67,7 +67,7 @@ jobs:
 
     - name: "Verify API for libkeymancore*.so (${{ steps.environment_step.outputs.GIT_BRANCH }}, branch ${{ steps.environment_step.outputs.GIT_BASE_BRANCH }}, by ${{ steps.environment_step.outputs.GIT_USER }})"
       run: |
-        echo "Verify API for libkeymancore*.so (${{ steps.environment_step.outputs.GIT_BRANCH }}, branch ${{ steps.environment_step.outputs.GIT_BASE_BRANCH }}, by ${{ steps.environment_step.outputs.GIT_USER }})" >> $GITHUB_STEP_SUMMARY
+        echo "Verify API for libkeymancore*.so (${{ steps.environment_step.outputs.GIT_BRANCH }}, branch ${{ steps.environment_step.outputs.GIT_BASE_BRANCH }}, by ${{ steps.environment_step.outputs.GIT_USER }}):" >> $GITHUB_STEP_SUMMARY
 
         BIN_PACKAGE=$(ls "${GITHUB_WORKSPACE}/artifacts/" | grep "${PKG_NAME}[0-9]*_${{ steps.environment_step.outputs.VERSION }}-1${{ steps.environment_step.outputs.PRERELEASE_TAG }}+$(lsb_release -c -s)1_amd64.deb")
         cd ${{ github.workspace }}/keyman/linux
diff --git a/HISTORY.md b/HISTORY.md
index b442c74e502..e46274077fe 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,5 +1,18 @@
 # Keyman Version History
 
+## 18.0.128 alpha 2024-10-14
+
+* docs(developer): add refs to Keyman MIME types (#12540)
+
+## 18.0.127 alpha 2024-10-12
+
+* fix(developer): use TextDecoder to convert Uint8Array to string (#12537)
+
+## 18.0.126 alpha 2024-10-11
+
+* test(common): add markdown link check test for product documentation (#12472)
+* chore(linux): improve output if `dpkg-gensymbols` fails and run other tests (#12527)
+
 ## 18.0.125 alpha 2024-10-10
 
 * chore(common): allow to run `build.sh` scripts in `bashdb` debugger (#12518)
diff --git a/VERSION.md b/VERSION.md
index 689f7b264ea..494d2a8106d 100644
--- a/VERSION.md
+++ b/VERSION.md
@@ -1 +1 @@
-18.0.126
\ No newline at end of file
+18.0.129
\ No newline at end of file
diff --git a/android/build.sh b/android/build.sh
index d876d882d77..859fcc56ff6 100755
--- a/android/build.sh
+++ b/android/build.sh
@@ -14,6 +14,7 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 
 builder_describe \
   "Build Keyman Engine for Android, Keyman for Android, and FirstVoices Android app." \
+  "@/resources/tools/check-markdown  test:help" \
   clean \
   configure \
   build \
@@ -23,6 +24,7 @@ builder_describe \
   --upload-sentry+ \
   ":engine=KMEA                             Keyman Engine for Android" \
   ":app=KMAPro                              Keyman for Android" \
+  ":help                                    Online documentation" \
   ":sample1=Samples/KMSample1               Sample app: KMSample1" \
   ":sample2=Samples/KMSample2               Sample app: KMSample2" \
   ":keyboardharness=Tests/KeyboardHarness   Test app: KeyboardHarness" \
@@ -42,4 +44,7 @@ if builder_start_action clean; then
   builder_finish_action success clean
 fi
 
-builder_run_child_actions configure build test publish
+builder_run_child_actions configure build test
+builder_run_action        test:help    check-markdown  "$KEYMAN_ROOT/android/docs/help"
+
+builder_run_child_actions publish
\ No newline at end of file
diff --git a/developer/docs/help/reference/file-types/kmp.md b/developer/docs/help/reference/file-types/kmp.md
index b79bd663be4..034de23b4d5 100644
--- a/developer/docs/help/reference/file-types/kmp.md
+++ b/developer/docs/help/reference/file-types/kmp.md
@@ -21,6 +21,8 @@ Details:
     Developer will also include a [metadata](metadata) file in the
     package. Lexical model packages contain one lexical model instead of
     keyboards.
+:   .kmp file format has registered MIME type
+    [`application/vnd.keyman.kmp+zip`](https://www.iana.org/assignments/media-types/application/vnd.keyman.kmp+zip).
 
 Distributed with keyboard:
 :   A Keyman keyboard Package file (.KMP) can include keyboard files
diff --git a/developer/docs/help/reference/file-types/kmx.md b/developer/docs/help/reference/file-types/kmx.md
index a4351688a52..062c18a2a9d 100644
--- a/developer/docs/help/reference/file-types/kmx.md
+++ b/developer/docs/help/reference/file-types/kmx.md
@@ -3,7 +3,7 @@ title: KMX files
 ---
 
 Used by:
-:   <span class="application">Keyman Desktop</span>,
+:   Keyman Core in <span class="application">Keyman for Windows</span>,
     <span class="application">Keyman for macOS</span>, and
     <span class="application">Keyman for Linux</span>.
 
@@ -16,6 +16,8 @@ Details:
     for the keyboard (.ICO/.BMP). Note that .KMX files are not used for
     <span class="application">Keyman for Android</span> and
     <span class="application">Keyman for iPhone and iPad</span>.
+:   .KMX file format has registered MIME type
+    [`application/vnd.keyman.kmx`](https://www.iana.org/assignments/media-types/application/vnd.keyman.kmx).
 
 Distributed with keyboard:
 :   This is the keyboard file. It must be distributed with your package
diff --git a/developer/src/build.sh b/developer/src/build.sh
index cde9b7fc233..bbae5f629ef 100755
--- a/developer/src/build.sh
+++ b/developer/src/build.sh
@@ -11,6 +11,7 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 
 builder_describe \
   "Keyman Developer" \
+  "@/resources/tools/check-markdown  test:help" \
   clean \
   configure \
   build \
@@ -20,6 +21,7 @@ builder_describe \
   "install                      Install built programs locally" \
   ":common                      Developer common files" \
   ":ext                         Third party components" \
+  ":help                        Online documentation" \
   ":kmcmplib                    Compiler - .kmn compiler" \
   ":kmc-analyze                 Compiler - Analysis Tools" \
   ":kmc-keyboard-info           Compiler - .keyboard_info Module" \
@@ -125,6 +127,7 @@ fi
 #-------------------------------------------------------------------------------------------------------------------
 
 builder_run_child_actions  clean configure build test
+builder_run_action         test:help    check-markdown  "$KEYMAN_ROOT/developer/docs/help"
 
 #-------------------------------------------------------------------------------------------------------------------
 
diff --git a/developer/src/common/web/utils/src/types/kpj/kpj-file-reader.ts b/developer/src/common/web/utils/src/types/kpj/kpj-file-reader.ts
index f86879b0068..8baeaef612b 100644
--- a/developer/src/common/web/utils/src/types/kpj/kpj-file-reader.ts
+++ b/developer/src/common/web/utils/src/types/kpj/kpj-file-reader.ts
@@ -14,7 +14,7 @@ export class KPJFileReader {
     let data: KPJFile;
 
     data = new KeymanXMLReader('kpj')
-      .parse(file.toString());
+      .parse(new TextDecoder().decode(file));
 
     data = this.boxArrays(data);
     if(data.KeymanDeveloperProject?.Files?.File?.length) {
diff --git a/developer/src/common/web/utils/src/types/kvks/kvks-file-reader.ts b/developer/src/common/web/utils/src/types/kvks/kvks-file-reader.ts
index 9f2ca18f887..1048d7dc888 100644
--- a/developer/src/common/web/utils/src/types/kvks/kvks-file-reader.ts
+++ b/developer/src/common/web/utils/src/types/kvks/kvks-file-reader.ts
@@ -22,7 +22,7 @@ export default class KVKSFileReader {
 
     try {
       source = new KeymanXMLReader('kvks')
-        .parse(file.toString()) as KVKSourceFile;
+        .parse(new TextDecoder().decode(file)) as KVKSourceFile;
     } catch(e) {
       if(file.byteLength > 4 && file.subarray(0,3).every((v,i) => v == KVK_HEADER_IDENTIFIER_BYTES[i])) {
         throw new Error('File appears to be a binary .kvk file', {cause: e});
diff --git a/developer/src/common/web/utils/src/types/ldml-keyboard/ldml-keyboard-xml-reader.ts b/developer/src/common/web/utils/src/types/ldml-keyboard/ldml-keyboard-xml-reader.ts
index 17ade173931..92669716ea1 100644
--- a/developer/src/common/web/utils/src/types/ldml-keyboard/ldml-keyboard-xml-reader.ts
+++ b/developer/src/common/web/utils/src/types/ldml-keyboard/ldml-keyboard-xml-reader.ts
@@ -302,7 +302,7 @@ export class LDMLKeyboardXMLSourceFileReader {
 
   loadTestDataUnboxed(file: Uint8Array): any {
     const source = new KeymanXMLReader('keyboardTest3')
-      .parse(file.toString()) as any;
+      .parse(new TextDecoder().decode(file)) as any;
     return source;
   }
 
diff --git a/developer/src/kmc-package/src/compiler/kmp-compiler.ts b/developer/src/kmc-package/src/compiler/kmp-compiler.ts
index 1708d69704c..e256c37b88d 100644
--- a/developer/src/kmc-package/src/compiler/kmp-compiler.ts
+++ b/developer/src/kmc-package/src/compiler/kmp-compiler.ts
@@ -183,7 +183,7 @@ export class KmpCompiler implements KeymanCompiler {
 
         try {
           a = new KeymanXMLReader('kps')
-            .parse(data.toString()) as KpsFile.KpsPackage;
+            .parse(data) as KpsFile.KpsPackage;
         } catch(e) {
           this.callbacks.reportMessage(PackageCompilerMessages.Error_InvalidPackageFile({e}));
         }
diff --git a/ios/build.sh b/ios/build.sh
index 21a0be28277..fe007760369 100755
--- a/ios/build.sh
+++ b/ios/build.sh
@@ -1,23 +1,21 @@
 #!/usr/bin/env bash
-
 ## START STANDARD BUILD SCRIPT INCLUDE
 # adjust relative paths as necessary
 THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 . "${THIS_SCRIPT%/*}/../resources/build/builder.inc.sh"
 ## END STANDARD BUILD SCRIPT INCLUDE
 
-# Include our resource functions; they're pretty useful!
 . "$KEYMAN_ROOT/resources/shellHelperFunctions.sh"
 
-# Please note that this build script (understandably) assumes that it is running on Mac OS X.
-verify_on_mac
-
 builder_describe "Builds Keyman Engine and the Keyman app for use on iOS devices - iPhone and iPad." \
+  "@/resources/tools/check-markdown  test:help" \
   "clean" \
   "configure" \
   "build" \
+  "test" \
   ":engine                      Builds KeymanEngine.xcframework, usable by our main app and by third-party apps" \
   ":app=keyman                  Builds the Keyman app for iOS platforms" \
+  ":help                        Online documentation" \
   ":sample1=Samples/KMSample1   Builds the first KeymanEngine sample app" \
   ":sample2=Samples/KMSample2   Builds the second KeymanEngine sample app" \
   ":fv=../oem/firstvoices/ios   Builds OEM FirstVoices for iOS platforms" \
@@ -25,4 +23,5 @@ builder_describe "Builds Keyman Engine and the Keyman app for use on iOS devices
 
 builder_parse "$@"
 
-builder_run_child_actions clean configure build
\ No newline at end of file
+builder_run_child_actions clean configure build test
+builder_run_action        test:help    check-markdown  "$KEYMAN_ROOT/ios/docs/help"
diff --git a/linux/build.sh b/linux/build.sh
index 1012b7eb1f0..6b97c287f5a 100755
--- a/linux/build.sh
+++ b/linux/build.sh
@@ -6,12 +6,16 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 . "${THIS_SCRIPT%/*}/../resources/build/builder.inc.sh"
 ## END STANDARD BUILD SCRIPT INCLUDE
 
+. "$KEYMAN_ROOT/resources/shellHelperFunctions.sh"
+
 ################################ Main script ################################
 
 builder_describe \
   "Build Keyman for Linux." \
+  "@/resources/tools/check-markdown  test:help" \
   ":config=keyman-config             keyman-config" \
   ":engine=ibus-keyman               ibus-keyman" \
+  ":help                             Online documentation" \
   ":service=keyman-system-service    keyman-system-service" \
   "clean" \
   "configure" \
@@ -36,3 +40,4 @@ test_action() {
 }
 
 builder_run_action test test_action
+builder_run_action        test:help    check-markdown  "$KEYMAN_ROOT/linux/docs/help"
diff --git a/linux/scripts/verify_api.inc.sh b/linux/scripts/verify_api.inc.sh
index adaa9187c27..8334bc84b89 100644
--- a/linux/scripts/verify_api.inc.sh
+++ b/linux/scripts/verify_api.inc.sh
@@ -32,8 +32,12 @@ check_api_not_changed() {
   trap "rm -rf \"${tmpDir}\"" ERR
   dpkg -x "${BIN_PKG}" "${tmpDir}"
   mkdir -p debian/tmp/DEBIAN
-  dpkg-gensymbols -v"${VERSION}" -p"${PKG_NAME}" -e"${tmpDir}"/usr/lib/x86_64-linux-gnu/"${LIB_NAME}".so* -c4
-  output_ok "${LIB_NAME} API didn't change"
+  if dpkg-gensymbols -v"${VERSION}" -p"${PKG_NAME}" -e"${tmpDir}"/usr/lib/x86_64-linux-gnu/"${LIB_NAME}".so* -c4; then
+    output_ok "${LIB_NAME} API didn't change"
+  else
+    output_error "${LIB_NAME} API changed"
+    EXIT_CODE=4
+  fi
   cd "${REPO_ROOT}/linux"
   rm -rf "${tmpDir}"
   trap ERR
diff --git a/mac/build.sh b/mac/build.sh
index fbca48bd05f..8f17ba868d2 100755
--- a/mac/build.sh
+++ b/mac/build.sh
@@ -5,13 +5,13 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 . "${THIS_SCRIPT%/*}/../resources/build/builder.inc.sh"
 ## END STANDARD BUILD SCRIPT INCLUDE
 
-# Include our resource functions; they're pretty useful!
 . "$KEYMAN_ROOT/resources/shellHelperFunctions.sh"
 . "$KEYMAN_ROOT/resources/build/build-help.inc.sh"
 . "$KEYMAN_ROOT/mac/mac-utils.inc.sh"
 
 builder_describe "Builds Keyman for macOS." \
   "@/core:mac" \
+  "@/resources/tools/check-markdown  test:help" \
   "clean" \
   "configure" \
   "build" \
@@ -20,12 +20,10 @@ builder_describe "Builds Keyman for macOS." \
   "install     Installs result of Keyman4MacIM locally." \
   ":engine     KeymanEngine4Mac" \
   ":app        Keyman4MacIM" \
+  ":help       Online documentation" \
   ":testapp    Keyman4Mac (test harness)" \
   "--quick,-q  Bypasses notarization for $(builder_term install)"
 
-# Please note that this build script (understandably) assumes that it is running on Mac OS X.
-verify_on_mac
-
 builder_parse "$@"
 
 # Default is release build of Engine and (code-signed) Input Method
@@ -89,8 +87,8 @@ UPLOAD_SENTRY=false
 
 # Import local environment variables for build
 #
-# /mac/localenv.sh can be used to define CERTIFICATE_ID, 
-# APPSTORECONNECT_PROVIDER, APPSTORECONNECT_USERNAME, 
+# /mac/localenv.sh can be used to define CERTIFICATE_ID,
+# APPSTORECONNECT_PROVIDER, APPSTORECONNECT_USERNAME,
 # APPSTORECONNECT_PASSWORD, DEVELOPMENT_TEAM variables;
 # see /mac/README.md for details.
 #
@@ -304,6 +302,7 @@ builder_run_action build:testapp  do_build_testapp
 
 builder_run_action test:engine    execBuildCommand $ENGINE_NAME "xcodebuild -project \"$KME4M_PROJECT_PATH\" $BUILD_OPTIONS test -scheme $ENGINE_NAME"
 builder_run_action test:app       execBuildCommand "$IM_NAME-tests" "xcodebuild test -workspace \"$KMIM_WORKSPACE_PATH\" $CODESIGNING_SUPPRESSION $BUILD_OPTIONS -scheme Keyman SYMROOT=\"$KM4MIM_BASE_PATH/build\""
+builder_run_action test:help      check-markdown  "$KEYMAN_ROOT/mac/docs/help"
 
 builder_run_action install do_install
 
diff --git a/package-lock.json b/package-lock.json
index 8cf9c5d5d83..38d3d0ae136 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -7,6 +7,7 @@
       "name": "root",
       "workspaces": [
         "resources/gosh",
+        "resources/tools/check-markdown",
         "resources/tools/strip-emoji",
         "resources/build/version",
         "core/include/ldml",
@@ -6476,6 +6477,10 @@
         "url": "https://github.com/chalk/chalk-template?sponsor=1"
       }
     },
+    "node_modules/check-markdown": {
+      "resolved": "resources/tools/check-markdown",
+      "link": true
+    },
     "node_modules/chokidar": {
       "version": "3.5.1",
       "dev": true,
@@ -15310,6 +15315,95 @@
         "gosh": "gosh.js"
       }
     },
+    "resources/tools/check-markdown": {
+      "version": "1.0.0",
+      "license": "MIT",
+      "devDependencies": {
+        "chalk": "^2.4.2",
+        "marked": "^14.1.2"
+      }
+    },
+    "resources/tools/check-markdown/node_modules/ansi-styles": {
+      "version": "3.2.1",
+      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-3.2.1.tgz",
+      "integrity": "sha512-VT0ZI6kZRdTh8YyJw3SMbYm/u+NqfsAxEpWO0Pf9sq8/e94WxxOpPKx9FR1FlyCtOVDNOQ+8ntlqFxiRc+r5qA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "color-convert": "^1.9.0"
+      },
+      "engines": {
+        "node": ">=4"
+      }
+    },
+    "resources/tools/check-markdown/node_modules/chalk": {
+      "version": "2.4.2",
+      "resolved": "https://registry.npmjs.org/chalk/-/chalk-2.4.2.tgz",
+      "integrity": "sha512-Mti+f9lpJNcwF4tWV8/OrTTtF1gZi+f8FqlyAdouralcFWFQWF2+NgCHShjkCb+IFBLq9buZwE1xckQU4peSuQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "ansi-styles": "^3.2.1",
+        "escape-string-regexp": "^1.0.5",
+        "supports-color": "^5.3.0"
+      },
+      "engines": {
+        "node": ">=4"
+      }
+    },
+    "resources/tools/check-markdown/node_modules/color-convert": {
+      "version": "1.9.3",
+      "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-1.9.3.tgz",
+      "integrity": "sha512-QfAUtd+vFdAtFQcC8CCyYt1fYWxSqAiK2cSD6zDB8N3cpsEBAvRxp9zOGg6G/SHHJYAT88/az/IuDGALsNVbGg==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "color-name": "1.1.3"
+      }
+    },
+    "resources/tools/check-markdown/node_modules/color-name": {
+      "version": "1.1.3",
+      "resolved": "https://registry.npmjs.org/color-name/-/color-name-1.1.3.tgz",
+      "integrity": "sha512-72fSenhMw2HZMTVHeCA9KCmpEIbzWiQsjN+BHcBbS9vr1mtt+vJjPdksIBNUmKAW8TFUDPJK5SUU3QhE9NEXDw==",
+      "dev": true,
+      "license": "MIT"
+    },
+    "resources/tools/check-markdown/node_modules/has-flag": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-3.0.0.tgz",
+      "integrity": "sha512-sKJf1+ceQBr4SMkvQnBDNDtf4TXpVhVGateu0t918bl30FnbE2m4vNLX+VWe/dpjlb+HugGYzW7uQXH98HPEYw==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=4"
+      }
+    },
+    "resources/tools/check-markdown/node_modules/marked": {
+      "version": "14.1.2",
+      "resolved": "https://registry.npmjs.org/marked/-/marked-14.1.2.tgz",
+      "integrity": "sha512-f3r0yqpz31VXiDB/wj9GaOB0a2PRLQl6vJmXiFrniNwjkKdvakqJRULhjFKJpxOchlCRiG5fcacoUZY5Xa6PEQ==",
+      "dev": true,
+      "license": "MIT",
+      "bin": {
+        "marked": "bin/marked.js"
+      },
+      "engines": {
+        "node": ">= 18"
+      }
+    },
+    "resources/tools/check-markdown/node_modules/supports-color": {
+      "version": "5.5.0",
+      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-5.5.0.tgz",
+      "integrity": "sha512-QjVjwdXIt408MIiAqCX4oUKsgU2EqAGzs2Ppkm4aQYbjm+ZEWEcW4SfFNTr4uMNZma0ey4f5lgLrkB0aX0QMow==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "has-flag": "^3.0.0"
+      },
+      "engines": {
+        "node": ">=4"
+      }
+    },
     "resources/tools/strip-emoji": {
       "name": "stripemoji",
       "version": "1.0.0",
diff --git a/package.json b/package.json
index 2c06c1652c8..51228544692 100644
--- a/package.json
+++ b/package.json
@@ -32,6 +32,7 @@
   "scripts": {},
   "workspaces": [
     "resources/gosh",
+    "resources/tools/check-markdown",
     "resources/tools/strip-emoji",
     "resources/build/version",
     "core/include/ldml",
diff --git a/resources/shellHelperFunctions.sh b/resources/shellHelperFunctions.sh
index a3f419382e9..6f8e1b52681 100755
--- a/resources/shellHelperFunctions.sh
+++ b/resources/shellHelperFunctions.sh
@@ -301,3 +301,7 @@ _select_node_version_with_nvm() {
     builder_die "Attempted to select node.js version $REQUIRED_NODE_VERSION but found $CURRENT_NODE_VERSION instead"
   fi
 }
+
+check-markdown() {
+  node "$KEYMAN_ROOT/resources/tools/check-markdown" --root "$1"
+}
\ No newline at end of file
diff --git a/resources/tools/check-markdown/.gitignore b/resources/tools/check-markdown/.gitignore
new file mode 100644
index 00000000000..d16386367f7
--- /dev/null
+++ b/resources/tools/check-markdown/.gitignore
@@ -0,0 +1 @@
+build/
\ No newline at end of file
diff --git a/resources/tools/check-markdown/README.md b/resources/tools/check-markdown/README.md
new file mode 100644
index 00000000000..0f01787c105
--- /dev/null
+++ b/resources/tools/check-markdown/README.md
@@ -0,0 +1,20 @@
+# check-markdown
+
+This tool is used to test the validity of internal links within product
+documentation, e.g. `/android/docs/help/**/*.md`.
+
+It currently tests that:
+
+1. Markdown can be parsed
+2. Links to other files in the same section exist (with or without .md extension)
+3. Images exist
+
+It will also optionally report on:
+
+1. External absolute links (starting with http/https)
+2. Relative links outside the root of the help documentation
+3. Unnecessary use of .md extension in links
+
+We could extend it to include:
+
+1. Checks for anchor validity
diff --git a/resources/tools/check-markdown/build.sh b/resources/tools/check-markdown/build.sh
new file mode 100755
index 00000000000..607be1dea63
--- /dev/null
+++ b/resources/tools/check-markdown/build.sh
@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+## START STANDARD BUILD SCRIPT INCLUDE
+# adjust relative paths as necessary
+THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
+. "${THIS_SCRIPT%/*}/../../../resources/build/builder.inc.sh"
+## END STANDARD BUILD SCRIPT INCLUDE
+
+. "$KEYMAN_ROOT/resources/shellHelperFunctions.sh"
+
+################################ Main script ################################
+
+builder_describe "Check markdown internal links" \
+  "clean" \
+  "configure" \
+  "build"
+
+builder_describe_outputs \
+  configure          /node_modules \
+  build              build/index.js
+
+builder_parse "$@"
+
+builder_run_action clean      rm -rf build/ tsconfig.tsbuildinfo
+builder_run_action configure  verify_npm_setup
+builder_run_action build      tsc --build
+# builder_run_action test       mocha
diff --git a/resources/tools/check-markdown/package.json b/resources/tools/check-markdown/package.json
new file mode 100644
index 00000000000..16c85f65a49
--- /dev/null
+++ b/resources/tools/check-markdown/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "check-markdown",
+  "version": "1.0.0",
+  "type": "module",
+  "main": "build/index.js",
+  "license": "MIT",
+  "devDependencies": {
+    "marked": "^14.1.2",
+    "chalk": "^2.4.2"
+  }
+}
diff --git a/resources/tools/check-markdown/src/check-link.ts b/resources/tools/check-markdown/src/check-link.ts
new file mode 100644
index 00000000000..08df0b001d2
--- /dev/null
+++ b/resources/tools/check-markdown/src/check-link.ts
@@ -0,0 +1,60 @@
+import * as fs from 'node:fs';
+import { posix as path } from 'node:path';
+
+import { Tokens } from 'marked';
+
+import { LinkRef, LinkRefMessage } from './types.js';
+
+export function checkLinks(root: string, links: LinkRef[]) {
+  let result = true;
+  for(const file of links) {
+    for(const link of file.links) {
+      // verify that the file exists in filesystem at expected location
+      result = checkLink(root, file.file, <Tokens.Link>link, file.messages) && result;
+    }
+  }
+  return result;
+}
+
+function checkLink(root: string, file: string, token: Tokens.Link | Tokens.Image, messages: LinkRefMessage[]) {
+  const parsed = token.href.split('#');
+  const href = parsed[0];
+  // const anchor = parsed.length > 1 ? parsed[1] : '';
+
+  if(href.startsWith('https:') || href.startsWith('http:')) {
+    messages.push({token, type:'info', message: 'External link'});
+    return true;
+  }
+
+  if(href.startsWith('/')) {
+    messages.push({token, type:'info', message: 'Absolute path'});
+    return true;
+  }
+
+  const p = path.normalize(path.join(path.dirname(file), href));
+  if(p.startsWith('../') || p == '..') {
+    messages.push({token, type:'info', message: 'Relative path outside root'});
+    return true;
+  }
+
+  let fullPath = path.join(root, p);
+  if(token.type == 'link') {
+    if(fs.existsSync(fullPath) && fs.statSync(fullPath).isDirectory()) {
+      fullPath = path.join(fullPath, 'index.md');
+    } else if(fullPath.endsWith('.md')) {
+      messages.push({token, type:'warning', message: 'Link should not have a .md extension'});
+    } else if(!fs.existsSync(fullPath)) {
+      // TODO: consider testing other file extensions in future?
+      fullPath = fullPath + '.md';
+    }
+  }
+
+  if(!fs.existsSync(fullPath)) {
+    fullPath = path.relative(root, fullPath);
+    messages.push({token, type:'error', message: `Link target '${fullPath}' does not exist`});
+    return false;
+  }
+
+  // TODO: check anchor
+  return true;
+}
diff --git a/resources/tools/check-markdown/src/find-files.ts b/resources/tools/check-markdown/src/find-files.ts
new file mode 100644
index 00000000000..76c7f1b5775
--- /dev/null
+++ b/resources/tools/check-markdown/src/find-files.ts
@@ -0,0 +1,9 @@
+import * as fs from 'node:fs';
+
+export function findFiles(root: string) {
+  const files: string[] = fs.readdirSync(root, {
+    recursive: true, encoding: 'utf-8'
+  }).map(file => file.replace(/\\/g, '/'));
+
+  return files;
+}
diff --git a/resources/tools/check-markdown/src/index.ts b/resources/tools/check-markdown/src/index.ts
new file mode 100644
index 00000000000..0ca8f25320c
--- /dev/null
+++ b/resources/tools/check-markdown/src/index.ts
@@ -0,0 +1,52 @@
+import { posix as path } from 'node:path';
+
+import chalk from 'chalk';
+import { Command } from 'commander';
+
+import { severityColors, type LinkRef } from './types.js';
+import { checkLinks } from './check-link.js';
+import { findFiles } from './find-files.js';
+import { parseFiles } from './parse-files.js';
+
+const color = chalk.default;
+
+const program = new Command();
+const command = program
+  .description('Markdown link and sanity checker')
+  .requiredOption('-r, --root <path>', 'Root path to check')
+  .option('-v, --verbose', 'Report on external links and warnings')
+  .action(run);
+
+program.parse(process.argv);
+
+function run() {
+  const root = command.opts().root;
+  const verbose = program.opts().verbose;
+
+  const files = findFiles(root);
+  const links = parseFiles(root, files);
+  const checkLinksSucceeded = checkLinks(root, links);
+
+  for(const file of links) {
+    if(file.messages.length) {
+      reportMessages(root, checkLinksSucceeded && verbose /* only give verbose output if no errors */, file);
+    }
+  }
+
+  process.exit(checkLinksSucceeded ? 0 : 1);
+}{
+
+}
+function reportMessages(root: string, verbose: boolean, file: LinkRef) {
+  for(const message of file.messages) {
+    if(message.type == 'error' || verbose) {
+      process.stdout.write(
+          color.cyan(path.join(root, file.file)) + ' - ' +
+          severityColors[message.type](message.type) + ': ' +
+          message.message +
+          color.grey(' [' + message.token.text + '](' + message.token.href + ')') +
+          '\n'
+      );
+    }
+  }
+}
diff --git a/resources/tools/check-markdown/src/parse-files.ts b/resources/tools/check-markdown/src/parse-files.ts
new file mode 100644
index 00000000000..ea98db1bab9
--- /dev/null
+++ b/resources/tools/check-markdown/src/parse-files.ts
@@ -0,0 +1,30 @@
+import * as fs from 'node:fs';
+import { posix as path } from 'node:path';
+
+import { marked, Token } from 'marked';
+
+import { type LinkRef } from './types.js';
+
+let refLinks: any[] = [];
+
+const walkTokens = (token: Token) => {
+  if (token.type === 'link' || token.type === 'image') {
+    refLinks.push(token);
+  }
+};
+
+marked.use( { walkTokens });
+
+export function parseFiles(root: string, files: string[]): LinkRef[] {
+  const links: LinkRef[] = [];
+  for (const file of files) {
+    const fullPath = path.join(root, file);
+    if (fs.statSync(fullPath).isFile() && fullPath.endsWith('.md')) {
+      refLinks = [];
+      marked.parse(fs.readFileSync(fullPath, 'utf-8'));
+      links.push({ file, links: refLinks, messages: [] });
+    }
+  }
+
+  return links;
+}
diff --git a/resources/tools/check-markdown/src/types.ts b/resources/tools/check-markdown/src/types.ts
new file mode 100644
index 00000000000..7f310674cc7
--- /dev/null
+++ b/resources/tools/check-markdown/src/types.ts
@@ -0,0 +1,20 @@
+import chalk from 'chalk';
+import { Token, Tokens } from 'marked';
+
+const color = chalk.default;
+
+export type MessageType = 'info' | 'warning' | 'error';
+
+export const severityColors: {[value in MessageType]: chalk.Chalk} = {
+  'info': color.reset,
+  'warning': color.hex('FFA500'), // orange
+  'error': color.redBright,
+};
+
+export interface LinkRefMessage {
+  type: MessageType;
+  message: string;
+  token: Tokens.Link | Tokens.Image;
+};
+
+export interface LinkRef {file: string, links: Token[], messages: LinkRefMessage[]};
diff --git a/resources/tools/check-markdown/tsconfig.json b/resources/tools/check-markdown/tsconfig.json
new file mode 100644
index 00000000000..74778aad7c3
--- /dev/null
+++ b/resources/tools/check-markdown/tsconfig.json
@@ -0,0 +1,9 @@
+{
+  "extends": "../../../tsconfig.base.json",
+
+	"compilerOptions": {
+    "baseUrl": "./",
+		"outDir": "./build/",
+		"rootDir": "src/",
+  },
+}
diff --git a/windows/src/build.sh b/windows/src/build.sh
index 4ef6da65b86..c6768a6d92c 100755
--- a/windows/src/build.sh
+++ b/windows/src/build.sh
@@ -5,9 +5,13 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 . "${THIS_SCRIPT%/*}/../../resources/build/builder.inc.sh"
 ## END STANDARD BUILD SCRIPT INCLUDE
 
+. "$KEYMAN_ROOT/resources/shellHelperFunctions.sh"
+
 builder_describe \
   "Keyman for Windows" \
   \
+  "@/resources/tools/check-markdown  test:help" \
+  \
   clean \
   configure \
   build \
@@ -17,6 +21,7 @@ builder_describe \
   \
   ":engine                 Keyman Engine for Windows" \
   ":desktop                Keyman for Windows" \
+  ":help                   Online documentation" \
   ":components=global/delphi   Delphi components" \
   ":support                Support tools" \
   ":test=test/unit-tests   Shared unit tests" \
@@ -24,4 +29,6 @@ builder_describe \
 
 builder_parse "$@"
 
-builder_run_child_actions  clean configure build test publish install
+builder_run_child_actions  clean configure build test
+builder_run_action         test:help      check-markdown  "$KEYMAN_ROOT/windows/docs/help"
+builder_run_child_actions  publish install