diff --git a/README.md b/README.md
index a112396..f0f81fe 100644
--- a/README.md
+++ b/README.md
@@ -230,15 +230,17 @@ sh docs/standards/playbook/scripts/sync_standards.sh tsl cpp
 - `docs/standards/playbook/scripts/sync_standards.bat`（推荐，支持多语言参数）
 - 脚本会从快照目录同步到项目根目录，并先备份旧文件（`.bak.*`）。
 
-注：建议固定使用 `--prefix docs/standards/playbook`，因为同步后的 `.agents/*/`
-会引用该路径下的标准快照文档（`docs/standards/playbook/docs/...`）。注：默认同步到
-`.agents/tsl/`；如需同步 C++ 规则集，推荐直接运行：`sh docs/standards/playbook/scripts/sync_standards.sh tsl cpp`。
+建议固定使用 `--prefix docs/standards/playbook`，因为同步后的 `.agents/*/`
+会引用该路径下的标准快照文档（`docs/standards/playbook/docs/...`）。无参数时若已存在
+`.agents/<lang>/`，将按现有语言同步；否则默认 `.agents/tsl/`。如需同步 C++ 规则集，
+推荐直接运行：`sh docs/standards/playbook/scripts/sync_standards.sh tsl cpp`。
 
 这样 clone 任意项目时都能直接读取规范文件，不依赖外部访问权限。
 
 同步脚本行为（目标项目内的最终落地内容）：
 
 - 覆盖/更新：`.agents/<AGENTS_NS>/`（默认 `.agents/tsl/`）
+- 自动识别：未传语言参数且已存在 `.agents/<lang>/` 时，按现有语言同步
 - 更新 `.gitattributes`：默认追加缺失规则（可用
   `SYNC_GITATTR_MODE=append|block|overwrite|skip` 控制）
 - 缺省创建：`.agents/index.md`
diff --git a/scripts/sync_standards.bat b/scripts/sync_standards.bat
index 1c2a837..67b571c 100644
--- a/scripts/sync_standards.bat
+++ b/scripts/sync_standards.bat
@@ -21,27 +21,30 @@ for %%I in ("%SCRIPT_DIR%..") do set "SRC=%%~fI"
 set "AGENTS_SRC_ROOT=%SRC%\.agents"
 set "GITATTR_SRC=%SRC%\.gitattributes"
 set "AGENTS_NS=%AGENTS_NS%"
-if "%AGENTS_NS%"=="" set "AGENTS_NS=tsl"
-echo %AGENTS_NS%| findstr /r "[\\/]" >nul && (
-  echo ERROR: invalid AGENTS_NS=%AGENTS_NS%
-  exit /b 1
-)
-echo %AGENTS_NS%| findstr /c:".." >nul && (
-  echo ERROR: invalid AGENTS_NS=%AGENTS_NS%
-  exit /b 1
-)
-set "AGENTS_ROOT=%ROOT%\.agents"
-set "AGENTS_DST=%AGENTS_ROOT%\%AGENTS_NS%"
 set "GITATTR_DST=%ROOT%\.gitattributes"
 set "SYNC_GITATTR_MODE=%SYNC_GITATTR_MODE%"
 if "%SYNC_GITATTR_MODE%"=="" set "SYNC_GITATTR_MODE=append"
 
 rem Multi rulesets: only on outer invocation.
 if "%SYNC_STANDARDS_INNER%"=="" (
-  if not "%~1"=="" (
+  set "LANG_LIST="
+  if not "%~1"=="" set "LANG_LIST=%*"
+  if "%LANG_LIST%"=="" (
+    if "%AGENTS_NS%"=="" (
+      if exist "%ROOT%\.agents" (
+        for /d %%D in ("%ROOT%\.agents\*") do (
+          set "CAND=%%~nxD"
+          if exist "%AGENTS_SRC_ROOT%\!CAND!\" (
+            if defined LANG_LIST (set "LANG_LIST=!LANG_LIST! !CAND!") else set "LANG_LIST=!CAND!"
+          )
+        )
+      )
+    )
+  )
+  if not "%LANG_LIST%"=="" (
     set "FIRST=1"
     set "SYNC_FIRST=%SYNC_GITATTR_MODE%"
-    for %%L in (%*) do (
+    for %%L in (!LANG_LIST!) do (
       if "!FIRST!"=="1" (
         set "FIRST=0"
         set "SYNC_STANDARDS_INNER=1"
@@ -59,6 +62,18 @@ if "%SYNC_STANDARDS_INNER%"=="" (
   )
 )
 
+if "%AGENTS_NS%"=="" set "AGENTS_NS=tsl"
+echo %AGENTS_NS%| findstr /r "[\\/]" >nul && (
+  echo ERROR: invalid AGENTS_NS=%AGENTS_NS%
+  exit /b 1
+)
+echo %AGENTS_NS%| findstr /c:".." >nul && (
+  echo ERROR: invalid AGENTS_NS=%AGENTS_NS%
+  exit /b 1
+)
+set "AGENTS_ROOT=%ROOT%\.agents"
+set "AGENTS_DST=%AGENTS_ROOT%\%AGENTS_NS%"
+
 set "AGENTS_SRC=%AGENTS_SRC_ROOT%\%AGENTS_NS%"
 if not exist "%AGENTS_SRC%" (
   rem Backward-compatible fallback: older snapshots used ^<snapshot^>\.agents\* directly.
diff --git a/scripts/sync_standards.ps1 b/scripts/sync_standards.ps1
index 0a2aba7..6f13791 100644
--- a/scripts/sync_standards.ps1
+++ b/scripts/sync_standards.ps1
@@ -31,6 +31,17 @@ if (-not (Test-Path $AgentsSrcRoot)) {
 
 $timestamp = Get-Date -Format "yyyyMMddHHmmss"
 
+# Auto-detect languages from existing .agents when no args are provided.
+if (-not $env:SYNC_STANDARDS_INNER -and (-not $Langs -or $Langs.Count -eq 0) -and -not $env:AGENTS_NS) {
+  $agentsRoot = Join-Path $Root ".agents"
+  if (Test-Path $agentsRoot) {
+    $autoLangs = @(Get-ChildItem -Path $agentsRoot -Directory | ForEach-Object { $_.Name } | Where-Object { Test-Path (Join-Path $AgentsSrcRoot $_) })
+    if ($autoLangs.Count -gt 0) {
+      $Langs = $autoLangs
+    }
+  }
+}
+
 # Multi rulesets: only on the outer invocation.
 if (-not $env:SYNC_STANDARDS_INNER -and $Langs -and $Langs.Count -gt 0) {
   $oldInner = $env:SYNC_STANDARDS_INNER
diff --git a/scripts/sync_standards.sh b/scripts/sync_standards.sh
index 6c3dd8f..7639dbd 100644
--- a/scripts/sync_standards.sh
+++ b/scripts/sync_standards.sh
@@ -47,6 +47,21 @@ if [ "${SYNC_STANDARDS_INNER:-}" != "1" ]; then
   if [ -z "${langs:-}" ] && [ "$#" -gt 0 ]; then
     langs="$*"
   fi
+  if [ -z "${langs:-}" ] && [ "$#" -eq 0 ] && [ -z "${AGENTS_NS:-}" ]; then
+    auto_langs=""
+    if [ -d "$ROOT/.agents" ]; then
+      for dir in "$ROOT/.agents"/*; do
+        [ -d "$dir" ] || continue
+        ns="$(basename "$dir")"
+        if [ -d "$AGENTS_SRC_ROOT/$ns" ]; then
+          auto_langs="${auto_langs:+$auto_langs }$ns"
+        fi
+      done
+    fi
+    if [ -n "$auto_langs" ]; then
+      langs="$auto_langs"
+    fi
+  fi
   if [ -n "${langs:-}" ]; then
     sync_mode_first="${SYNC_GITATTR_MODE:-append}"
 
@@ -162,29 +177,38 @@ if [ -f "$GITATTR_SRC" ]; then
       if [ "$(CDPATH= cd -- "$(dirname -- "$GITATTR_SRC")" && pwd -P)/$(basename -- "$GITATTR_SRC")" = "$GITATTR_DST" ]; then
         echo "Skip: .gitattributes source equals destination."
       else
-        if [ -f "$GITATTR_DST" ]; then
-          dst_file="$GITATTR_DST"
-        else
-          dst_file="/dev/null"
-        fi
         missing_tmp="$(mktemp 2>/dev/null || echo "$ROOT/.gitattributes.missing.$timestamp")"
-        awk '
-          function norm(line) {
-            gsub(/^[ \t]+|[ \t]+$/, "", line)
-            return line
-          }
-          FNR==NR {
-            line=norm($0)
-            if (line == "" || line ~ /^#/) next
-            seen[line]=1
-            next
-          }
-          {
-            line=norm($0)
-            if (line == "" || line ~ /^#/) next
-            if (!seen[line] && !out[line]++) print line
-          }
-        ' "$dst_file" "$GITATTR_SRC" >"$missing_tmp"
+        if [ -f "$GITATTR_DST" ]; then
+          awk '
+            function norm(line) {
+              gsub(/^[ \t]+|[ \t]+$/, "", line)
+              return line
+            }
+            FNR==NR {
+              line=norm($0)
+              if (line == "" || line ~ /^#/) next
+              seen[line]=1
+              next
+            }
+            {
+              line=norm($0)
+              if (line == "" || line ~ /^#/) next
+              if (!seen[line] && !out[line]++) print line
+            }
+          ' "$GITATTR_DST" "$GITATTR_SRC" >"$missing_tmp"
+        else
+          awk '
+            function norm(line) {
+              gsub(/^[ \t]+|[ \t]+$/, "", line)
+              return line
+            }
+            {
+              line=norm($0)
+              if (line == "" || line ~ /^#/) next
+              if (!out[line]++) print line
+            }
+          ' "$GITATTR_SRC" >"$missing_tmp"
+        fi
 
         if [ ! -s "$missing_tmp" ]; then
           rm -f "$missing_tmp"
diff --git a/tests/README.md b/tests/README.md
index 64a6b80..ea0ac56 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -68,7 +68,7 @@ sh check_doc_links.sh
 
 - **基础功能**：
   - 脚本存在且可执行
-  - 无参数时默认同步 tsl 规则集
+  - 无参数时默认同步 tsl（已有 `.agents/<lang>/` 则自动识别）
   - 单语言同步（tsl/cpp）
   - 多语言同步（tsl cpp）
 - **.gitattributes 同步**：
diff --git a/tests/scripts/test_sync_standards.bats b/tests/scripts/test_sync_standards.bats
index 988f657..20f1884 100644
--- a/tests/scripts/test_sync_standards.bats
+++ b/tests/scripts/test_sync_standards.bats
@@ -22,6 +22,7 @@ setup() {
 teardown() {
     # 清理测试目录
     if [ -n "$TEST_DIR" ] && [ -d "$TEST_DIR" ]; then
+        chmod -R u+rwX "$TEST_DIR" 2>/dev/null || true
         rm -rf "$TEST_DIR"
     fi
 }
@@ -43,6 +44,18 @@ teardown() {
     [ -f ".agents/tsl/index.md" ]
 }
 
+@test "sync_standards.sh 无参数时自动识别已有语言" {
+    cd "$TEST_DIR"
+    mkdir -p .agents/cpp
+    echo "# placeholder" > .agents/cpp/index.md
+
+    sh "$SCRIPT_PATH"
+
+    [ -d ".agents/cpp" ]
+    [ -f ".agents/cpp/index.md" ]
+    [ ! -d ".agents/tsl" ]
+}
+
 @test "sync_standards.sh tsl - 同步 TSL 规则集" {
     cd "$TEST_DIR"
     sh "$SCRIPT_PATH" tsl