diff --git a/.github/workflows/export_game_modes.yml b/.github/workflows/export_game_modes.yml
new file mode 100644
index 00000000000..913da8fbaf6
--- /dev/null
+++ b/.github/workflows/export_game_modes.yml
@@ -0,0 +1,143 @@
+name: Export Game Modes JSON
+
+on:
+  push:
+    branches:
+      - stable
+      - master
+  workflow_dispatch:
+
+env:
+  EXPORT_DIR: /tmp/bar-export
+  MAP_NAME: quicksilver_remake_1.24.sd7
+  MAP_URL: https://springfiles.springrts.com/files/maps/quicksilver_remake_1.24.sd7
+
+jobs:
+  export:
+    name: Export Game Modes
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    if: github.repository == 'beyond-all-reason/Beyond-All-Reason'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Resolve engine version
+        id: engine
+        run: |
+          CONFIG=$(curl -fsSL https://launcher-config.beyondallreason.dev/config.json)
+          ENGINE_URL=$(echo "$CONFIG" | jq -r '
+            .setups[]
+            | select(.package.id == "manual-linux-test-engine")
+            | .downloads.resources[]
+            | select(.destination | contains("engine"))
+            | .url
+          ')
+          ENGINE_DEST=$(echo "$CONFIG" | jq -r '
+            .setups[]
+            | select(.package.id == "manual-linux-test-engine")
+            | .downloads.resources[]
+            | select(.destination | contains("engine"))
+            | .destination
+          ')
+          ENGINE_VERSION=$(basename "$ENGINE_DEST")
+          echo "url=$ENGINE_URL" >> "$GITHUB_OUTPUT"
+          echo "dest=$ENGINE_DEST" >> "$GITHUB_OUTPUT"
+          echo "version=$ENGINE_VERSION" >> "$GITHUB_OUTPUT"
+          echo "Resolved engine: $ENGINE_VERSION"
+
+      - name: Cache engine and map
+        id: cache
+        uses: actions/cache@v4
+        with:
+          path: |
+            ${{ env.EXPORT_DIR }}/engine
+            ${{ env.EXPORT_DIR }}/maps
+          key: modes-export-${{ steps.engine.outputs.version }}-quicksilver-1.24
+
+      - name: Download engine
+        if: steps.cache.outputs.cache-hit != 'true'
+        run: |
+          mkdir -p "$EXPORT_DIR/${{ steps.engine.outputs.dest }}"
+          curl -fsSL "${{ steps.engine.outputs.url }}" -o /tmp/engine.7z
+          7z x /tmp/engine.7z -o"$EXPORT_DIR/${{ steps.engine.outputs.dest }}"
+          rm /tmp/engine.7z
+
+      - name: Download map
+        if: steps.cache.outputs.cache-hit != 'true'
+        run: |
+          mkdir -p "$EXPORT_DIR/maps"
+          curl -fsSL "$MAP_URL" -o "$EXPORT_DIR/maps/$MAP_NAME"
+
+      - name: Set up workspace
+        run: |
+          mkdir -p "$EXPORT_DIR/games"
+          ln -sf "$GITHUB_WORKSPACE" "$EXPORT_DIR/games/BAR.sdd"
+          cp tools/headless_testing/springsettings.cfg "$EXPORT_DIR/"
+          cp tools/headless_testing/startscript_modes_export.txt "$EXPORT_DIR/"
+
+      - name: Run headless export
+        run: |
+          cd "$EXPORT_DIR"
+          rm -rf LuaUI/Config
+          engine/*/spring-headless \
+            --isolation \
+            --write-dir "$(pwd)" \
+            startscript_modes_export.txt
+        timeout-minutes: 15
+
+      - name: Validate export
+        run: |
+          OUT="$EXPORT_DIR/game_modes.json"
+          if [ ! -f "$OUT" ]; then
+            echo "::error::Export produced no game_modes.json"
+            exit 1
+          fi
+          # Must be valid JSON with the expected schema and at least one category.
+          CATEGORIES=$(jq -e '.schemaVersion as $v
+            | if $v != 1 then error("unexpected schemaVersion \($v)") else . end
+            | .categories | length' "$OUT")
+          echo "Exported $CATEGORIES mode categories (schemaVersion 1)"
+          if [ "$CATEGORIES" -lt 1 ]; then
+            echo "::error::Export has no mode categories"
+            exit 1
+          fi
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: game-modes-${{ github.sha }}
+          path: ${{ env.EXPORT_DIR }}/game_modes.json
+
+      # push -> rolling per-channel asset (stable/test); workflow_dispatch -> commit-pinned
+      # asset only (off-master test builds), pruned to newest 50. Both feed the SPADS plugin.
+      - name: Publish to release
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh release view game-modes >/dev/null 2>&1 \
+            || gh release create game-modes \
+                 --prerelease \
+                 --title "Game Modes Export" \
+                 --notes "Game mode presets, regenerated by export_game_modes.yml and self-fetched by the SPADS ModeCommand plugin. Not a code release." \
+                 --target "${{ github.sha }}" \
+            || true
+          if [ "${{ github.event_name }}" = "workflow_dispatch" ]; then
+            ASSET="game_modes-${GITHUB_SHA:0:7}.json"
+            cp "$EXPORT_DIR/game_modes.json" "$EXPORT_DIR/$ASSET"
+            gh release upload game-modes "$EXPORT_DIR/$ASSET" --clobber
+            echo "Published commit-pinned $ASSET"
+            gh release view game-modes --json assets \
+              -q '.assets[] | select(.name | test("^game_modes-[0-9a-f]{7}\\.json$")) | [.createdAt, .name] | @tsv' \
+              | sort -r | tail -n +51 | cut -f2 | while read -r OLD; do
+                  gh release delete-asset game-modes "$OLD" -y && echo "Pruned $OLD"
+                done
+          else
+            CHANNEL=stable
+            [ "${{ github.ref_name }}" = "stable" ] || CHANNEL=test
+            ASSET="game_modes-${CHANNEL}.json"
+            cp "$EXPORT_DIR/game_modes.json" "$EXPORT_DIR/$ASSET"
+            gh release upload game-modes "$EXPORT_DIR/$ASSET" --clobber
+            echo "Published channel $ASSET"
+          fi
diff --git a/luaui/Widgets/export_game_modes.lua b/luaui/Widgets/export_game_modes.lua
new file mode 100644
index 00000000000..a0a671d7f59
--- /dev/null
+++ b/luaui/Widgets/export_game_modes.lua
@@ -0,0 +1,116 @@
+local widget = widget ---@type Widget
+
+function widget:GetInfo()
+	return {
+		name = "Game Modes JSON Export",
+		desc = "Exports all game mode presets (modes/<category>/*.lua) to structured JSON.\nCommand: /exportgamemodes",
+		author = "Daniel Harvey",
+		date = "June 2026",
+		license = "GNU GPL, v2 or later",
+		layer = 0,
+		enabled = false,
+	}
+end
+
+-- Emit the Lua mode presets overlaid on modoptions.lua defaults as JSON so out-of-engine
+-- consumers (SPADS ModeCommand plugin) can expand a mode selection into its full option set.
+
+local spEcho = Spring.Echo
+
+local SCHEMA_VERSION = 1
+local OUTPUT_PATH = "game_modes.json"
+
+-- modoptions are strings; booleans -> "1"/"0", numbers rounded at float32 precision to avoid noise.
+local function toModOptionValue(v)
+	if type(v) == "boolean" then
+		return v and "1" or "0"
+	end
+	if type(v) == "number" then
+		local s = string.format("%.7f", v):gsub("0+$", ""):gsub("%.$", "")
+		return s
+	end
+	return tostring(v)
+end
+
+-- Each modoption section becomes a mode category's default base: section name == category.
+local function collectDefaultsBySection()
+	local bySection = {}
+	for _, o in ipairs(VFS.Include("modoptions.lua")) do
+		if o.key and o.section and o.def ~= nil and o.type ~= "section" and o.type ~= "subheader" and o.type ~= "separator" then
+			bySection[o.section] = bySection[o.section] or {}
+			bySection[o.section][o.key] = toModOptionValue(o.def)
+		end
+	end
+	return bySection
+end
+
+-- Discover every mode under modes/<category>/*.lua (root helpers and key/category-less returns skipped).
+local function collectModesByCategory()
+	local byCategory = {}
+	for _, dir in ipairs(VFS.SubDirs("modes/") or {}) do
+		for _, modeFile in ipairs(VFS.DirList(dir, "*.lua") or {}) do
+			local ok, mode = pcall(VFS.Include, modeFile)
+			if ok and type(mode) == "table" and mode.key and mode.category then
+				byCategory[mode.category] = byCategory[mode.category] or {}
+				byCategory[mode.category][mode.key] = mode
+			end
+		end
+	end
+	return byCategory
+end
+
+-- Full effective option set (defaults then overrides), so applying a mode resets the previous one.
+local function buildEffectiveModOptions(defaults, mode, selector)
+	local effective = {}
+	for key, value in pairs(defaults) do
+		if key ~= selector then
+			effective[key] = { value = value, locked = false }
+		end
+	end
+	for key, rule in pairs(mode.modOptions or {}) do
+		if key ~= selector and rule.value ~= nil then
+			effective[key] = { value = toModOptionValue(rule.value), locked = rule.locked == true }
+		end
+	end
+	return effective
+end
+
+local function buildExport()
+	local defaultsBySection = collectDefaultsBySection()
+	local modesByCategory = collectModesByCategory()
+
+	local categories = {}
+	for category, modes in pairs(modesByCategory) do
+		local selector = category .. "_mode"
+		local defaults = defaultsBySection[category] or {}
+		local presets = {}
+		for modeKey, mode in pairs(modes) do
+			presets[modeKey] = {
+				name = mode.name,
+				desc = mode.desc,
+				allowRanked = mode.allowRanked,
+				modOptions = buildEffectiveModOptions(defaults, mode, selector),
+			}
+		end
+		categories[category] = { selector = selector, presets = presets }
+	end
+
+	return { schemaVersion = SCHEMA_VERSION, categories = categories }
+end
+
+local function ExportGameModes()
+	local file, err = io.open(OUTPUT_PATH, "w")
+	if not file then
+		spEcho("Game Modes JSON Export: could not open " .. OUTPUT_PATH .. ": " .. tostring(err))
+		return
+	end
+	file:write(Json.encode(buildExport()))
+	file:close()
+	spEcho("Game Modes JSON Export: wrote " .. OUTPUT_PATH)
+end
+
+function widget:TextCommand(command)
+	if command == "exportgamemodes" then
+		ExportGameModes()
+	end
+end
diff --git a/tools/headless_testing/startscript_modes_export.txt b/tools/headless_testing/startscript_modes_export.txt
new file mode 100644
index 00000000000..14ca66834d3
--- /dev/null
+++ b/tools/headless_testing/startscript_modes_export.txt
@@ -0,0 +1,28 @@
+[GAME]
+{
+	MapName=Quicksilver Remake 1.24;
+	GameType=Beyond All Reason $VERSION;
+	GameStartDelay=0;
+	StartPosType=0;
+	RecordDemo=0;
+	MyPlayerName=TestRunner;
+	IsHost=1;
+	FixedRNGSeed = 1;
+  [MODOPTIONS]
+  {
+    debugcommands=1:luaui enablewidget Game Modes JSON Export|2:exportgamemodes|3:quitforce;
+		deathmode=neverend;
+  }
+  [ALLYTEAM0]
+  {
+  }
+  [TEAM0]
+  {
+    allyteam=0;
+    teamleader=0;
+  }
+  [PLAYER0]
+  {
+    team=0;
+  }
+}