diff --git a/common/web/types/src/consts/modifier-key-constants.ts b/common/web/types/src/consts/modifier-key-constants.ts
index 1f09c183f1..cfa8f03b01 100644
--- a/common/web/types/src/consts/modifier-key-constants.ts
+++ b/common/web/types/src/consts/modifier-key-constants.ts
@@ -189,3 +189,42 @@ export function visualKeyboardShiftToLayerName(shift: VisualKeyboardShiftState):
   }
   return result.substring(0, result.length - 1);
 }
+
+/**
+ * Get modifier key state from a hyphen-separated modifier string, such as
+ * found in layer ids or key "layer" properties. Ignores unrecognized
+ * components. Order of components is not significant.
+ *
+ * @param   modifierString     a modifier string such as 'ctrl-shift'
+ * @return  Keyman modifier state bitmask
+ */
+export function modifierStringToState(modifierString: string): ModifierKeyConstant {
+  const map = new Map<string,ModifierKeyConstant>([
+    ['shift',     ModifierKeyConstant.K_SHIFTFLAG],
+    ['leftctrl',  ModifierKeyConstant.LCTRLFLAG],
+    ['rightctrl', ModifierKeyConstant.RCTRLFLAG],
+    ['ctrl',      ModifierKeyConstant.K_CTRLFLAG],
+    ['leftalt',   ModifierKeyConstant.LALTFLAG],
+    ['rightalt',  ModifierKeyConstant.RALTFLAG],
+    ['alt',       ModifierKeyConstant.K_ALTFLAG],
+    ['caps',      ModifierKeyConstant.CAPITALFLAG],
+    // legacy mappings: these were deprecated when we introduced chiral
+    // modifiers in KeymanWeb in ~v14.0; typically these would have been used
+    // without other components, but for the purposes of this function, we can
+    // treat them as components without harm
+    ['altshift',     ModifierKeyConstant.K_ALTFLAG | ModifierKeyConstant.K_SHIFTFLAG],
+    ['ctrlalt',      ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_ALTFLAG],
+    ['ctrlaltshift', ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_ALTFLAG | ModifierKeyConstant.K_SHIFTFLAG],
+    ['ctrlshift',    ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_SHIFTFLAG],
+  ]);
+
+  let modifier = 0;
+  const components = modifierString.split('-');
+  for(const component of components) {
+    if(map.has(component)) {
+      modifier |= map.get(component);
+    }
+  }
+
+  return modifier;
+}
diff --git a/common/web/types/src/main.ts b/common/web/types/src/main.ts
index 3b5664279d..06cff791c4 100644
--- a/common/web/types/src/main.ts
+++ b/common/web/types/src/main.ts
@@ -20,6 +20,7 @@ export {
   ModifierKeyConstant, ModifierKeyConstants, LDML_MODIFIER_TO_KVK_MODIFIER, KVK_MODIFIER_TO_LDML_MODIFIER,
   translateLdmlModifiersToVisualKeyboardShift, translateVisualKeyboardShiftToLdmlModifiers,
   visualKeyboardShiftToLayerName,
+  modifierStringToState,
 } from './consts/modifier-key-constants.js';
 
 export * as TouchLayout from './keyman-touch-layout/keyman-touch-layout-file.js';
diff --git a/common/web/types/tests/consts/modifier-key-constants.tests.ts b/common/web/types/tests/consts/modifier-key-constants.tests.ts
new file mode 100644
index 0000000000..87ce5c062d
--- /dev/null
+++ b/common/web/types/tests/consts/modifier-key-constants.tests.ts
@@ -0,0 +1,31 @@
+/*
+ * Keyman is copyright (C) SIL Global. MIT License.
+ */
+
+import 'mocha';
+import { assert } from 'chai';
+import { ModifierKeyConstant, modifierStringToState } from '../../src/consts/modifier-key-constants.js';
+
+describe('modifierStringToState', function() {
+  it('should map modifiers correctly', function() {
+    assert.equal(modifierStringToState(''), 0);
+    assert.equal(modifierStringToState('shift'), ModifierKeyConstant.K_SHIFTFLAG);
+    assert.equal(modifierStringToState('ctrl'), ModifierKeyConstant.K_CTRLFLAG);
+    assert.equal(modifierStringToState('rightctrl'), ModifierKeyConstant.RCTRLFLAG);
+    assert.equal(modifierStringToState('ctrl-shift'), ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_SHIFTFLAG);
+    assert.equal(modifierStringToState('ctrl-shift-alt'), ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_SHIFTFLAG | ModifierKeyConstant.K_ALTFLAG);
+    assert.equal(modifierStringToState('ctrl-shift-alt-caps'), ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_SHIFTFLAG | ModifierKeyConstant.K_ALTFLAG | ModifierKeyConstant.CAPITALFLAG);
+    assert.equal(modifierStringToState('caps-alt-ctrl-shift'), ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_SHIFTFLAG | ModifierKeyConstant.K_ALTFLAG | ModifierKeyConstant.CAPITALFLAG);
+  });
+
+  it('should map legacy modifiers correctly', function() {
+    assert.equal(modifierStringToState('altshift'), ModifierKeyConstant.K_ALTFLAG | ModifierKeyConstant.K_SHIFTFLAG);
+    assert.equal(modifierStringToState('ctrlaltshift'), ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_SHIFTFLAG | ModifierKeyConstant.K_ALTFLAG);
+  });
+
+  it('should ignore unknown modifiers', function() {
+    assert.equal(modifierStringToState('ctrl-shift-none'), ModifierKeyConstant.K_CTRLFLAG | ModifierKeyConstant.K_SHIFTFLAG);
+    assert.equal(modifierStringToState('ctrlraltshift'), 0);
+    assert.equal(modifierStringToState('ncaps'), 0);
+  });
+});
diff --git a/web/src/engine/keyboard/src/codes.ts b/web/src/engine/keyboard/src/codes.ts
index c94d5b7152..4a8c9f2622 100644
--- a/web/src/engine/keyboard/src/codes.ts
+++ b/web/src/engine/keyboard/src/codes.ts
@@ -86,6 +86,7 @@ const Codes = {
   /**
    * Get modifier key state from layer id
    *
+   * @deprecated Use `modifierStringToState` from `@keymanapp/common-types`; note that 'caps' is also matched
    * @param       {string}      layerId       layer id (e.g. ctrlshift)
    * @return      {number}                    modifier key state (desktop keyboards)
    */
@@ -128,6 +129,7 @@ const Codes = {
   /**
    * Get state key state from layer id
    *
+   * @deprecated Use `modifierStringToState` from `@keymanapp/common-types`; note that modifiers are also matched
    * @param       {string}      layerId       layer id (e.g. caps)
    * @return      {number}                    modifier key state (desktop keyboards)
    */