diff --git a/common/linux/build.sh b/common/linux/build.sh
index 756826cc2d..b52102313e 100755
--- a/common/linux/build.sh
+++ b/common/linux/build.sh
@@ -18,7 +18,7 @@ builder_describe "Keyman common Linux modules" \
 
 builder_parse "$@"
 
-if [[ $BUILDER_OS != linux ]]; then
+if ! builder_is_linux; then
   builder_echo grey "Platform is not linux; skipping common/linux"
   exit 0
 fi
diff --git a/common/mac/build.sh b/common/mac/build.sh
index 392966d84c..44a7064c83 100755
--- a/common/mac/build.sh
+++ b/common/mac/build.sh
@@ -18,7 +18,7 @@ builder_describe "Keyman common mac modules" \
 
 builder_parse "$@"
 
-if [[ $BUILDER_OS != mac ]]; then
+if ! builder_is_macos; then
   builder_echo grey "Platform is not macOS; skipping common/mac"
   exit 0
 fi
diff --git a/common/test/resources/test_kill_browserstack.sh b/common/test/resources/test_kill_browserstack.sh
index 82e40f85cd..f6ea16a36b 100755
--- a/common/test/resources/test_kill_browserstack.sh
+++ b/common/test/resources/test_kill_browserstack.sh
@@ -12,7 +12,7 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 ## END STANDARD BUILD SCRIPT INCLUDE
 
 
-if [[ $BUILDER_OS == win ]]; then
+if builder_is_windows; then
   # BrowserStackLocal may not exist, so always pass
   taskkill //f //im BrowserStackLocal.exe || true
 fi
diff --git a/common/windows/build.sh b/common/windows/build.sh
index 06f5dd0201..663a7f41c7 100755
--- a/common/windows/build.sh
+++ b/common/windows/build.sh
@@ -18,7 +18,7 @@ builder_describe "Keyman common Windows modules" \
 
 builder_parse "$@"
 
-if [[ $BUILDER_OS != win ]]; then
+if ! builder_is_windows; then
   builder_echo grey "Platform is not Windows; skipping common/windows"
   exit 0
 fi
diff --git a/core/commands.inc.sh b/core/commands.inc.sh
index 761be3db4d..73ad033a8e 100644
--- a/core/commands.inc.sh
+++ b/core/commands.inc.sh
@@ -91,7 +91,7 @@ do_test() {
   if [[ $target =~ ^(x86|x64)$ ]]; then
     cmd //C build.bat $target $BUILDER_CONFIGURATION test $testparams
   else
-    if [[ $target == wasm ]] && [[ $BUILDER_OS == mac ]]; then
+    if [[ $target == wasm ]] && builder_is_macos; then
       # 11794 -- parallel tests failing on some mac build agents; temporary
       # mitigation until we diagnose root cause
       meson test -j 1 -C "$MESON_PATH" $testparams
@@ -136,7 +136,7 @@ do_uninstall() {
 # ----------------------------------------------------------------------------
 
 build_meson_cross_file_for_wasm() {
-  if [ $BUILDER_OS == win ]; then
+  if builder_is_windows; then
     local R=$(cygpath -w $(echo $EMSCRIPTEN_BASE) | sed 's_\\_\\\\_g')
   else
     local R=$(echo $EMSCRIPTEN_BASE | sed 's_/_\\/_g')
diff --git a/developer/src/build.sh b/developer/src/build.sh
index d01c6caeb8..d81762aa2c 100755
--- a/developer/src/build.sh
+++ b/developer/src/build.sh
@@ -66,7 +66,7 @@ builder_parse "$@"
 
 #-------------------------------------------------------------------------------------------------------------------
 
-if [[ $BUILDER_OS == win ]]; then
+if builder_is_windows; then
   source "$KEYMAN_ROOT/resources/build/win/environment.inc.sh"
 fi
 
diff --git a/developer/src/kmcmplib/commands.inc.sh b/developer/src/kmcmplib/commands.inc.sh
index 280343853c..e2a5679ed6 100644
--- a/developer/src/kmcmplib/commands.inc.sh
+++ b/developer/src/kmcmplib/commands.inc.sh
@@ -126,7 +126,7 @@ do_command() {
 # ----------------------------------------------------------------------------
 
 build_meson_cross_file_for_wasm() {
-  if [ $BUILDER_OS == win ]; then
+  if builder_is_windows; then
     local R=$(cygpath -w $(echo $EMSCRIPTEN_BASE) | sed 's_\\_\\\\_g')
   else
     local R=$(echo $EMSCRIPTEN_BASE | sed 's_/_\\/_g')
@@ -140,4 +140,4 @@ should_do_full_test() {
   fi
 
   return 1
-}
\ No newline at end of file
+}
diff --git a/docs/builder.md b/docs/builder.md
index 360a15a550..18272accd0 100644
--- a/docs/builder.md
+++ b/docs/builder.md
@@ -123,6 +123,13 @@ package.json (`npm run <script>`).
   passed in, or `release` otherwise, which corresponds to the output folder
   names for many projects.
 
+* `BUILDER_OS` will be set to `linux`, `mac`, or `win`, depending on the platform
+  the builder script is currently running on.
+
+  **NOTE:** Only use `BUILDER_OS` in a `case` statement. Use one of the
+  `builder_is_macos`, `builder_is_windows`, or `builder_is_linux` functions
+  to check if the script is running on a particular platform.
+
 Other environment variables and paths will probably be added over time.
 
 ## Split
@@ -1241,6 +1248,20 @@ builder_run_action  test    builder_do_typescript_tests [coverage_threshold]
 
 --------------------------------------------------------------------------------
 
+## `builder_is_windows`, `builder_is_macos`, and `builder_is_linux` functions
+
+Returns 0 (true) if building on the particular platform.
+
+### Usage
+
+```bash
+if builder_is_windows; then
+  builder_echo "We're building on a Windows machine"
+fi
+```
+
+--------------------------------------------------------------------------------
+
 ## Formatting variables
 
 These helper variables define ANSI color escapes when running in color mode, and
diff --git a/mac/Keyman4MacIM/make-km-dmg.sh b/mac/Keyman4MacIM/make-km-dmg.sh
index 84d09312c1..21559b59ff 100755
--- a/mac/Keyman4MacIM/make-km-dmg.sh
+++ b/mac/Keyman4MacIM/make-km-dmg.sh
@@ -7,7 +7,7 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 ## END STANDARD BUILD SCRIPT INCLUDE
 
 # Please note that this build script (understandably) assumes that it is running on Mac OS X.
-if [[ "${OSTYPE}" != "darwin"* ]]; then
+if ! builder_is_macos; then
   echo "This build script will only run in a Mac environment."
   exit 1
 fi
diff --git a/mac/Keyman4MacIM/write-download_info.sh b/mac/Keyman4MacIM/write-download_info.sh
index 656d0ce385..7f064727af 100755
--- a/mac/Keyman4MacIM/write-download_info.sh
+++ b/mac/Keyman4MacIM/write-download_info.sh
@@ -7,7 +7,7 @@ THIS_SCRIPT="$(readlink -f "${BASH_SOURCE[0]}")"
 ## END STANDARD BUILD SCRIPT INCLUDE
 
 # Please note that this build script (understandably) assumes that it is running on Mac OS X.
-if [[ "${OSTYPE}" != "darwin"* ]]; then
+if ! builder_is_macos; then
   echo "This build script will only run in a Mac environment."
   exit 1
 fi
diff --git a/resources/build/build-utils-ci.inc.sh b/resources/build/build-utils-ci.inc.sh
index b4fc88c252..bd9fc7995b 100644
--- a/resources/build/build-utils-ci.inc.sh
+++ b/resources/build/build-utils-ci.inc.sh
@@ -179,7 +179,7 @@ function _builder_prepublish() {
 
         builder_echo "Manually linking $link_source -> $link_target (see https://github.com/npm/cli/issues/3466)"
         rm -rf $link_source
-        if [[ $BUILDER_OS == win ]]; then
+        if builder_is_windows; then
           link_source="$(cygpath -w "$link_source")"
           link_target="$(cygpath -w "$link_target")"
           cmd //c mklink //j "$link_source" "$link_target"
diff --git a/resources/build/build-utils.sh b/resources/build/build-utils.sh
index 4996845c5a..003129aaad 100755
--- a/resources/build/build-utils.sh
+++ b/resources/build/build-utils.sh
@@ -205,26 +205,6 @@ printBuildNumberForTeamCity
 
 findShouldSentryRelease
 
-# Sets the BUILDER_OS environment variable to linux|mac|win
-#
-_builder_get_operating_system() {
-  declare -g BUILDER_OS
-  # Default value, since it's the most general case/configuration to detect.
-  BUILDER_OS=linux
-
-  # Subject to change with future improvements.
-  if [[ $OSTYPE == darwin* ]]; then
-    BUILDER_OS=mac
-  elif [[ $OSTYPE == msys ]]; then
-    BUILDER_OS=win
-  elif [[ $OSTYPE == cygwin ]]; then
-    BUILDER_OS=win
-  fi
-  readonly BUILDER_OS
-}
-
-_builder_get_operating_system
-
 # Intended for use with macOS-based builds, as Xcode build phase "run script"s do not have access to important
 # environment variables.  Doesn't hurt to run it at other times as well.  The output file is .gitignore'd.
 function exportEnvironmentDefinitionScript() {
@@ -259,7 +239,8 @@ function exportEnvironmentDefinitionScript() {
 # someone else to intentionally use, so this check seems reasonable.
 #
 # https://gist.github.com/gdavis/6670468 has a representative copy of a standard Xcode environment variable setup.
-if [ "$BUILDER_OS" == "mac" ] && [[ -z "${XCODE_VERSION_ACTUAL:-}" ]] && [[ -z "${XCODE_PRODUCT_BUILD_VERSION:-}" ]]; then
+# shellcheck disable=2310
+if builder_is_macos && [[ -z "${XCODE_VERSION_ACTUAL:-}" ]] && [[ -z "${XCODE_PRODUCT_BUILD_VERSION:-}" ]]; then
     exportEnvironmentDefinitionScript
 fi
 
diff --git a/resources/build/jq.inc.sh b/resources/build/jq.inc.sh
index d1d7c32c23..ebe460475b 100644
--- a/resources/build/jq.inc.sh
+++ b/resources/build/jq.inc.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 #
 # Setup JQ environment variable according to the user's system
 #
@@ -13,22 +13,17 @@ if [[ -z "${JQ+x}" ]]; then
   # . "${THIS_SCRIPT%/*}/build-utils.sh"
   ## END STANDARD BUILD SCRIPT INCLUDE
 
-  case "${OSTYPE}" in
-    "cygwin")
-      JQ=$(dirname "$JQ_THIS_SCRIPT")/jq-win64.exe
-      ;;
-    "msys")
-      JQ=$(dirname "$JQ_THIS_SCRIPT")/jq-win64.exe
-      ;;
-    *)
-      JQ=jq
-      ;;
-  esac
+  if builder_is_windows; then
+    JQ=$(dirname "${JQ_THIS_SCRIPT}")/jq-win64.exe
+  else
+    JQ=jq
+  fi
 
   readonly JQ
 
   # JQ with inplace file replacement
   function jqi() {
-    cat <<< "$($JQ -c "$1" < "$2")" > "$2"
+    # shellcheck disable=2312
+    cat <<< "$("${JQ}" -c "$1" < "$2")" > "$2"
   }
-fi
\ No newline at end of file
+fi
diff --git a/resources/build/zip.inc.sh b/resources/build/zip.inc.sh
index 1f80a71edb..14253660b9 100644
--- a/resources/build/zip.inc.sh
+++ b/resources/build/zip.inc.sh
@@ -51,14 +51,14 @@ function add_zip_files() {
         shift
         ;;
       -[0123456789])
-        # Compression level where 
+        # Compression level where
         # -0 indicates no compression
         # -1 indicates low compression (fastest)
         # -9 indicates ultra compression (slowest)
         ZIP_FLAGS+=($1)
         if [[ $1 =~ -([0-9]) ]]; then
           SEVENZ_FLAGS+=("-mx${BASH_REMATCH[1]}")
-        fi  
+        fi
         shift;
         ;;
 
@@ -80,14 +80,12 @@ function add_zip_files() {
   if ! command -v zip 2>&1 > /dev/null; then
     # Fallback to 7z
     if [[ -z "${SEVENZ+x}" ]]; then
-      case "${OSTYPE}" in
-        "cygwin"|"msys")
-          SEVENZ="${SEVENZ_HOME}"/7z.exe
-          ;;
-        *)
-          SEVENZ=7z
-          ;;
-      esac
+      if builder_is_windows; then
+        # shellcheck disable=2154
+        SEVENZ="${SEVENZ_HOME}/7z.exe"
+      else
+        SEVENZ=7z
+      fi
     fi
 
     # 7z command to add files so clear zip flags
diff --git a/resources/builder.inc.sh b/resources/builder.inc.sh
index a445509f95..a3422348d8 100755
--- a/resources/builder.inc.sh
+++ b/resources/builder.inc.sh
@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+# shellcheck shell=bash
 # shellcheck disable=SC2310
 
 # Note: these two lines can be uncommented for debugging and profiling build
@@ -33,6 +33,7 @@ SHLVL=0
 # _builder_init is called internally at the bottom of this file after we have
 # all function declarations in place.
 function _builder_init() {
+  _builder_get_operating_system
   _builder_findRepoRoot
   _builder_setBuildScriptIdentifiers
 
@@ -2090,27 +2091,14 @@ builder_describe_platform() {
 
   local builder_platforms=(linux mac win)
   local builder_tools=(android-studio delphi)
-
-  # --- Detect platform ---
-
-  # Default value, since it's the most general case/configuration to detect.
-  local builder_platform=linux
-
-  # This is copied from build-utils.sh to avoid creating a dependency on it
-  if [[ $OSTYPE == darwin* ]]; then
-    builder_platform=mac
-  elif [[ $OSTYPE == msys ]]; then
-    builder_platform=win
-  elif [[ $OSTYPE == cygwin ]]; then
-    builder_platform=win
-  fi
+  local builder_platform="${BUILDER_OS}"
 
   # --- Detect tools ---
 
   local builder_installed_tools=()
 
   # Detect delphi compiler (see also delphi_environment.inc.sh)
-  if [[ $builder_platform == win ]]; then
+  if builder_is_windows; then
     local ProgramFilesx86="$(cygpath -w -F 42)"
     if [[ -x "$(cygpath -u "$ProgramFilesx86\\Embarcadero\\Studio\\20.0\\bin\\dcc32.exe")" ]]; then
       builder_installed_tools+=(delphi)
@@ -2278,6 +2266,50 @@ builder_if_release_build_level() {
   "$@"
 }
 
+# Returns 0 if we're running on Windows, i.e. if the environment variable
+# `OSTYPE` is set to "msys" or "cygwin".
+builder_is_windows() {
+  if [[ "${OSTYPE:-}" == "msys" ]] || [[ "${OSTYPE:-}" == "cygwin" ]]; then
+    return 0
+  else
+    return 1
+  fi
+}
+
+# Returns 0 if we're running on macOS.
+builder_is_macos() {
+  if [[ "${OSTYPE:-}" == darwin* ]]; then
+    return 0
+  else
+    return 1
+  fi
+}
+
+# Returns 0 if we're running on Linux.
+builder_is_linux() {
+  if [[ "${OSTYPE:-}" == "linux-gnu" ]]; then
+    return 0
+  else
+    return 1
+  fi
+}
+
+# Sets the BUILDER_OS environment variable to linux|mac|win
+#
+_builder_get_operating_system() {
+  declare -g BUILDER_OS
+
+  if builder_is_macos; then
+    BUILDER_OS=mac
+  elif builder_is_windows; then
+    BUILDER_OS=win
+  else
+    BUILDER_OS=linux
+  fi
+
+  readonly BUILDER_OS
+}
+
 ################################################################################
 # Final initialization
 ################################################################################
diff --git a/resources/docker-images/docker-build.inc.sh b/resources/docker-images/docker-build.inc.sh
index 855ba6e641..9685116955 100644
--- a/resources/docker-images/docker-build.inc.sh
+++ b/resources/docker-images/docker-build.inc.sh
@@ -63,8 +63,8 @@ is_default_values() {
 # Check that `docker buildx` is available
 check_buildx_available() {
   if ! docker --help | grep -q buildx; then
-    if [[ "${OSTYPE:-}" == "linux-gnu" ]]; then
-      builder_echo error "Docker buildx is not available. Please install Docker buildx to use this script. e.g. 'sudo apt install docker-buildx'"
+    if builder_is_linux; then
+      builder_echo error "Docker buildx is not available. Please install Docker buildx to use this script. E.g. 'sudo apt install docker-buildx'"
     else
       builder_echo error "Docker buildx is not available. Please install Docker buildx to use this script."
     fi
diff --git a/resources/locate_emscripten.inc.sh b/resources/locate_emscripten.inc.sh
index d390e83bd2..43d0d39a70 100644
--- a/resources/locate_emscripten.inc.sh
+++ b/resources/locate_emscripten.inc.sh
@@ -20,7 +20,7 @@
 #
 locate_emscripten() {
   local EMCC_EXECUTABLE
-  if [[ "${BUILDER_OS}" == "win" ]]; then
+  if builder_is_windows; then
     EMCC_EXECUTABLE="emcc.py"
   else
     EMCC_EXECUTABLE="emcc"
diff --git a/resources/shellHelperFunctions.sh b/resources/shellHelperFunctions.sh
index 6b30918cb7..40cd40e0e3 100755
--- a/resources/shellHelperFunctions.sh
+++ b/resources/shellHelperFunctions.sh
@@ -6,7 +6,7 @@
 
 # Allows for a quick macOS check for those scripts requiring a macOS environment.
 verify_on_mac() {
-  if [[ "${OSTYPE}" != "darwin"* ]]; then
+  if ! builder_is_macos; then
     builder_die "This build script will only run in a Mac environment."
     exit 1
   fi
@@ -111,7 +111,7 @@ write_download_info() {
   _verify_project "${PLATFORM}"
 
   # shellcheck disable=SC2312
-  if [[ "${BUILDER_OS}" == "mac" ]] && [[ $(command -v stat) == /usr/bin/stat ]]; then
+  if builder_is_macos && [[ $(command -v stat) == /usr/bin/stat ]]; then
     # /usr/bin/stat on mac is BSD
     STAT_FLAGS="-f%z"
   else
@@ -271,24 +271,25 @@ verify_npm_setup() {
 }
 
 _print_expected_node_version() {
-"$JQ" -r '.engines.node' "$KEYMAN_ROOT/package.json"
+  "$JQ" -r '.engines.node' "$KEYMAN_ROOT/package.json"
 }
 
 # Use nvm to select a node version according to package.json
 # see /docs/build/node.md
 _select_node_version_with_nvm() {
-  local REQUIRED_NODE_VERSION="$(_print_expected_node_version)"
-  local CURRENT_NODE_VERSION
+  local REQUIRED_NODE_VERSION  CURRENT_NODE_VERSION
 
-  if [[ $BUILDER_OS != win ]]; then
-    # launch nvm in a sub process, see _builder_nvm.sh for details
-    "$KEYMAN_ROOT/resources/build/_builder_nvm.sh" "$REQUIRED_NODE_VERSION"
-  else
+  REQUIRED_NODE_VERSION="$(_print_expected_node_version)"
+
+  if builder_is_windows; then
     CURRENT_NODE_VERSION="$(node --version)"
-    if [[ "$CURRENT_NODE_VERSION" != "v$REQUIRED_NODE_VERSION" ]]; then
-      start //wait //b nvm install "$REQUIRED_NODE_VERSION"
-      start //wait //b nvm use "$REQUIRED_NODE_VERSION"
+    if [[ "${CURRENT_NODE_VERSION}" != "v${REQUIRED_NODE_VERSION}" ]]; then
+      start //wait //b nvm install "${REQUIRED_NODE_VERSION}"
+      start //wait //b nvm use "${REQUIRED_NODE_VERSION}"
     fi
+  else
+    # launch nvm in a sub process, see _builder_nvm.sh for details
+    "${KEYMAN_ROOT}/resources/build/_builder_nvm.sh" "${REQUIRED_NODE_VERSION}"
   fi
 
   # Now, check that the node version is correct, on all systems
diff --git a/resources/teamcity/android/keyman-android-release.sh b/resources/teamcity/android/keyman-android-release.sh
index 856a86424e..ce10a61d01 100755
--- a/resources/teamcity/android/keyman-android-release.sh
+++ b/resources/teamcity/android/keyman-android-release.sh
@@ -92,7 +92,7 @@ function _publish_to_playstore() {
 }
 
 function do_publish() {
-  if ! is_windows; then
+  if ! builder_is_windows; then
     # currently only tested on Windows, TODO: test cross-platform
     builder_echo error "This script is intended to be run on Windows only."
     return 1
diff --git a/resources/teamcity/common/common-test-core.sh b/resources/teamcity/common/common-test-core.sh
index 9ea781697a..6801967c67 100755
--- a/resources/teamcity/common/common-test-core.sh
+++ b/resources/teamcity/common/common-test-core.sh
@@ -22,11 +22,11 @@ builder_describe \
 
 builder_parse "$@"
 
-if is_ubuntu; then
+if builder_is_linux; then
   ARCH=arch
-elif is_windows; then
+elif builder_is_windows; then
   ARCH=win
-elif is_macos; then
+elif builder_is_macos; then
   ARCH=mac
 else
   builder_echo error "Unknown architecture"
diff --git a/resources/teamcity/developer/developer-actions.inc.sh b/resources/teamcity/developer/developer-actions.inc.sh
index c7fef7a5f4..cca98fc26f 100644
--- a/resources/teamcity/developer/developer-actions.inc.sh
+++ b/resources/teamcity/developer/developer-actions.inc.sh
@@ -2,7 +2,7 @@
 # Keyman is copyright (C) SIL Global. MIT License.
 
 developer_install_dependencies_on_linux_action() {
-  if ! is_ubuntu; then
+  if ! builder_is_linux; then
     return 0
   fi
 
diff --git a/resources/teamcity/developer/keyman-developer-release.sh b/resources/teamcity/developer/keyman-developer-release.sh
index 3977fe931f..ccec2b58ba 100755
--- a/resources/teamcity/developer/keyman-developer-release.sh
+++ b/resources/teamcity/developer/keyman-developer-release.sh
@@ -142,7 +142,7 @@ function build_developer_action() {
 }
 
 function publish_action() {
-  if ! is_windows; then
+  if ! builder_is_windows; then
     # requires Powershell, so currently only supported on Windows
     builder_echo error "This script is intended to be run on Windows only."
     return 1
diff --git a/resources/teamcity/developer/keyman-developer-test-linux-macos.sh b/resources/teamcity/developer/keyman-developer-test-linux-macos.sh
index c273873fe0..5b75299600 100755
--- a/resources/teamcity/developer/keyman-developer-test-linux-macos.sh
+++ b/resources/teamcity/developer/keyman-developer-test-linux-macos.sh
@@ -38,7 +38,7 @@ function build_developer_action() {
   builder_echo end "build developer" success "Finished building Keyman Developer"
 }
 
-if is_windows; then
+if builder_is_windows; then
   builder_echo error "This script is intended to be run on Linux or macOS only."
   exit 1
 fi
diff --git a/resources/teamcity/developer/keyman-developer-test-windows.sh b/resources/teamcity/developer/keyman-developer-test-windows.sh
index 604acb86b6..b0643f54bd 100755
--- a/resources/teamcity/developer/keyman-developer-test-windows.sh
+++ b/resources/teamcity/developer/keyman-developer-test-windows.sh
@@ -25,7 +25,7 @@ builder_describe \
 
 builder_parse "$@"
 
-if ! is_windows; then
+if ! builder_is_windows; then
   builder_echo error "This script is intended to be run on Windows only."
   exit 1
 fi
diff --git a/resources/teamcity/includes/tc-helpers.inc.sh b/resources/teamcity/includes/tc-helpers.inc.sh
index 05bac1b746..43ad9c1ba9 100644
--- a/resources/teamcity/includes/tc-helpers.inc.sh
+++ b/resources/teamcity/includes/tc-helpers.inc.sh
@@ -1,36 +1,8 @@
 # shellcheck shell=bash
 # Keyman is copyright (C) SIL Global. MIT License.
 
-# Returns 0 if we're running on Ubuntu.
-is_ubuntu() {
-  if [[ "${OSTYPE:-}" == "linux-gnu" ]]; then
-    return 0
-  else
-    return 1
-  fi
-}
-
-# Returns 0 if we're running on Windows, i.e. if the environment variable
-# `OSTYPE` is set to "msys" or "cygwin".
-is_windows() {
-  if [[ "${OSTYPE:-}" == "msys" ]] || [[ "${OSTYPE:-}" == "cygwin" ]]; then
-    return 0
-  else
-    return 1
-  fi
-}
-
-# Returns 0 if we're running on macOS.
-is_macos() {
-  if [[ "${OSTYPE:-}" == darwin* ]]; then
-    return 0
-  else
-    return 1
-  fi
-}
-
 install_nvm() {
-  if ! is_ubuntu; then
+  if ! builder_is_linux; then
     # on Windows and macOS build agents are configured manually
     return 0
   fi
@@ -55,7 +27,7 @@ set_variables_for_nvm() {
 }
 
 install_emscripten() {
-  if ! is_ubuntu; then
+  if ! builder_is_linux; then
     # on Windows and macOS build agents are configured manually
     return 0
   fi
@@ -92,7 +64,7 @@ _tc_rsync() {
     "--rsync-path=${RSYNC_PATH}"             # path on remote server
   )
 
-  if is_windows; then
+  if builder_is_windows; then
     rsync_args+=(
       '--chmod=Dug=rwx,Do=rx,Fug=rw,Fo=r'      # map Windows security to host security
       "--rsh=${RSYNC_HOME}\ssh -i ${USERPROFILE}\.ssh\id_rsa -o UserKnownHostsFile=${USERPROFILE}\.ssh\known_hosts"                  # use ssh
@@ -108,13 +80,13 @@ _tc_rsync() {
       "${DESTINATION}"
   )
 
-  if is_windows; then
+  if builder_is_windows; then
     local CYGPATH_RSYNC_HOME
     CYGPATH_RSYNC_HOME=$(cygpath -w "${RSYNC_HOME}")
     MSYS_NO_PATHCONV=1 "${CYGPATH_RSYNC_HOME}\\rsync.exe" "${rsync_args[@]}"
   else
     local RSYNC=rsync
-    if is_macos; then
+    if builder_is_macos; then
       RSYNC=/usr/local/bin/rsync
       [[ -f /opt/homebrew/bin/rsync ]] && RSYNC=/opt/homebrew/bin/rsync
     fi
diff --git a/resources/teamcity/includes/tc-linux.inc.sh b/resources/teamcity/includes/tc-linux.inc.sh
index 8e8db447a0..7f5f3ce4c4 100644
--- a/resources/teamcity/includes/tc-linux.inc.sh
+++ b/resources/teamcity/includes/tc-linux.inc.sh
@@ -25,7 +25,7 @@ _is_package_installed() {
 # Parameters:
 #   $* - List of package names to check and install (e.g., "lcov jq")
 ba_linux_check_and_install_packages() {
-  if ! is_ubuntu; then
+  if ! builder_is_linux; then
     return 0
   fi
 
diff --git a/resources/teamcity/web/keyman-web-release.sh b/resources/teamcity/web/keyman-web-release.sh
index 1c5cf0d88f..88fada4947 100755
--- a/resources/teamcity/web/keyman-web-release.sh
+++ b/resources/teamcity/web/keyman-web-release.sh
@@ -73,7 +73,7 @@ function publish_web_action() {
   builder_echo start publish "Publishing KeymanWeb release"
 
   # TODO: refactor to allow to run on Linux/macOS as well
-  if ! is_windows; then
+  if ! builder_is_windows; then
     builder_echo end publish error "Publishing KeymanWeb is only supported on Windows"
     return 1
   fi
diff --git a/resources/teamcity/web/web-actions.inc.sh b/resources/teamcity/web/web-actions.inc.sh
index e464c78940..bb54f38cb5 100644
--- a/resources/teamcity/web/web-actions.inc.sh
+++ b/resources/teamcity/web/web-actions.inc.sh
@@ -2,7 +2,7 @@
 # Keyman is copyright (C) SIL Global. MIT License.
 
 web_install_dependencies_on_linux_action() {
-  if ! is_ubuntu; then
+  if ! builder_is_linux; then
     return 0
   fi
 
@@ -18,7 +18,7 @@ web_install_dependencies_on_linux_action() {
 }
 
 _install_playwright_dependencies() {
-  if ! is_ubuntu || ! is_os_version_or_higher 24.04; then
+  if ! builder_is_linux || ! is_os_version_or_higher 24.04; then
     return 0
   fi
 
@@ -40,14 +40,14 @@ web_build_action() {
 
 web_test_action() {
   builder_echo start web_test "Running tests for native KeymanWeb"
-  if is_ubuntu; then
+  if builder_is_linux; then
     ba_linux_start_xvfb
     trap "ba_linux_stop_xvfb" ERR
   fi
 
   "${KEYMAN_ROOT}/web/ci.sh" test
 
-  if is_ubuntu; then
+  if builder_is_linux; then
     ba_linux_stop_xvfb
     trap ERR
   fi
diff --git a/resources/teamcity/windows/keyman-windows-release.sh b/resources/teamcity/windows/keyman-windows-release.sh
index 8e972f7b57..f82e31494f 100755
--- a/resources/teamcity/windows/keyman-windows-release.sh
+++ b/resources/teamcity/windows/keyman-windows-release.sh
@@ -36,7 +36,7 @@ builder_parse "$@"
 
 cd "${KEYMAN_ROOT}/windows/src"
 
-if ! is_windows; then
+if ! builder_is_windows; then
   builder_echo error "This script is intended to be run on Windows only."
   exit 1
 fi
diff --git a/resources/teamcity/windows/keyman-windows-test.sh b/resources/teamcity/windows/keyman-windows-test.sh
index 67705f20e1..8685fff4e3 100755
--- a/resources/teamcity/windows/keyman-windows-test.sh
+++ b/resources/teamcity/windows/keyman-windows-test.sh
@@ -30,7 +30,7 @@ builder_parse "$@"
 
 cd "${KEYMAN_ROOT}/windows/src"
 
-if ! is_windows; then
+if ! builder_is_windows; then
   builder_echo error "This script is intended to be run on Windows only."
   exit 1
 fi