diff --git a/.trellis/spec/backend/error-handling.md b/.trellis/spec/backend/error-handling.md
index fa5a9d4..4bbee31 100644
--- a/.trellis/spec/backend/error-handling.md
+++ b/.trellis/spec/backend/error-handling.md
@@ -37,8 +37,8 @@ subprocess.run(f"nssm.exe start {service_name}", shell=True)
 
 ## 服务状态错误
 
-- `sing start <name>` 在服务已运行时失败，并提示使用 `sing restart <name>`。
-- `sing restart <name>` 停止失败时不得继续启动。
+- `sing start <name>` 在服务已运行时失败，并提示使用 `sing restart`。
+- `sing restart` 停止失败时不得继续启动。
 - `sing stop` 在服务停止失败时返回失败。
 - `sing uninstall` 删除服务失败时返回失败。
 - 第一版不做隐式重试，不做自动修复服务状态。
@@ -46,7 +46,8 @@ subprocess.run(f"nssm.exe start {service_name}", shell=True)
 ## Profile 状态错误
 
 - profile 名不符合命名规则时失败。
-- `sing start <name>`、`sing restart <name>`、`sing update <name>` 找不到 profile 名时失败。
+- `sing start <name>`、`sing update <name>` 找不到 profile 名时失败。
+- `sing restart` 没有 active profile 或 active profile 不存在时失败。
 - `sing remove <name>` 删除 active profile 时失败。
 - 下载 profile URL 失败、HTTP 状态失败、写入本地文件失败时命令失败。
 - `sing add` 和 `sing update` 不主动调用 `sing-box check`；profile 有效性由 `sing start <name>` 启动时的 `sing-box` 行为暴露。
diff --git a/.trellis/spec/backend/index.md b/.trellis/spec/backend/index.md
index bc39297..d537ebd 100644
--- a/.trellis/spec/backend/index.md
+++ b/.trellis/spec/backend/index.md
@@ -40,7 +40,7 @@ sing install [--bin <path>]
 sing uninstall
 sing start <name>
 sing stop
-sing restart <name>
+sing restart
 sing add <name> <url>
 sing remove <name>
 sing update <name>
@@ -49,8 +49,8 @@ sing list
 
 - `sing install` 通过 NSSM 注册 `sing-box` Windows 服务并开启自启；默认使用 `PATH` 中的 `sing-box.exe`，`--bin` 可指定自定义路径。
 - `sing install` 不下载、不升级 `sing-box.exe` 或 `nssm.exe`，也不指定或写入业务 profile。
-- `sing start <name>` 使用 `<name>` 对应的本地 profile 启动服务；服务已运行时失败并提示使用 `sing restart <name>`。
-- `sing restart <name>` 停止当前服务后，用 `<name>` 对应 profile 重新启动。
+- `sing start <name>` 使用 `<name>` 对应的本地 profile 启动服务；服务已运行时失败并提示使用 `sing restart`。
+- `sing restart` 停止当前服务后，用 active profile 重新启动。
 - `sing stop` 停止服务，不需要 profile 名。
 - `sing add <name> <url>` 添加命名 profile；URL 返回完整 `sing-box` JSON profile。
 - `sing update <name>` 从已保存 URL 重新下载 profile。
@@ -59,13 +59,13 @@ sing list
 
 ## 服务命令行
 
-`sing start <name>` 和 `sing restart <name>` 启动前必须先更新 NSSM 服务参数：
+`sing start <name>` 和 `sing restart` 启动前必须先更新 NSSM 服务参数：
 
 ```text
 nssm.exe set sing-box Application <sing-box.exe>
 nssm.exe set sing-box AppParameters "run -c \"<profile-path>\""
 ```
 
-随后再启动 `sing-box` 服务。Windows 自启时沿用最后一次 `sing start <name>` 或 `sing restart <name>` 写入的 profile。
+随后再启动 `sing-box` 服务。Windows 自启时沿用最后一次 `sing start <name>` 或 `sing restart` 写入的 profile。
 
 调用 `nssm.exe` 必须使用参数列表，不使用 shell 字符串拼接。
diff --git a/.trellis/spec/backend/quality-guidelines.md b/.trellis/spec/backend/quality-guidelines.md
index b677f89..6311807 100644
--- a/.trellis/spec/backend/quality-guidelines.md
+++ b/.trellis/spec/backend/quality-guidelines.md
@@ -24,7 +24,7 @@ sing install [--bin <path>]
 sing uninstall
 sing start <name>
 sing stop
-sing restart <name>
+sing restart
 sing add <name> <url>
 sing remove <name>
 sing update <name>
@@ -33,7 +33,7 @@ sing list
 
 - `sing install` 通过 NSSM 注册服务并开启自启；不处理业务配置。
 - `sing start <name>` 负责把 NSSM 服务参数更新到 `<name>` 对应配置，再启动服务。
-- `sing restart <name>` 先停止服务，再更新 NSSM 服务参数并启动服务。
+- `sing restart` 先停止服务，再用 active 配置更新 NSSM 服务参数并启动服务。
 - `sing stop` 不需要配置名。
 - `sing list` 必须标出 active 配置。
 
@@ -60,7 +60,7 @@ nssm.exe remove sing-box confirm
 
 - `sing install [--bin <path>]` 解析 `sing-box.exe` 后调用 `nssm.exe install`，再设置 `Start` 为 `SERVICE_AUTO_START`。
 - `sing start <name>` 启动前设置 `Application` 为已安装的 `sing-box.exe` 路径，设置 `AppParameters` 为 `run -c "<profile-path>"`。
-- `sing restart <name>` 必须先停止服务，停止成功后再写入 NSSM 参数并启动服务。
+- `sing restart` 必须先停止服务，停止成功后再用 active 配置写入 NSSM 参数并启动服务。
 - `nssm.exe` 必须从 `PATH` 解析；项目不下载、不内置 NSSM。
 - 外部命令必须用参数列表调用，不通过 shell 字符串执行。
 - 捕获外部命令输出时必须显式使用 `encoding="utf-8"` 和 `errors="replace"`，避免 Windows locale 默认编码导致 reader thread 抛出 `UnicodeDecodeError`。
@@ -73,7 +73,9 @@ nssm.exe remove sing-box confirm
 | `nssm.exe` 返回非零退出码 | 命令失败并暴露 stderr 或 stdout 摘要 |
 | `nssm.exe` 输出包含当前系统编码无法解码的字节 | 命令不因解码崩溃，输出中的非法字节以替换字符呈现 |
 | `nssm.exe status sing-box` 输出 `SERVICE_RUNNING` | `service_is_running()` 返回 `True` |
-| `sing start <name>` 发现服务已运行 | 命令失败并提示使用 `sing restart <name>` |
+| `sing start <name>` 发现服务已运行 | 命令失败并提示使用 `sing restart` |
+| `sing restart` 没有 active 配置 | 命令失败并提示先运行 `sing start <name>` |
+| `sing restart` 的 active 配置不存在 | 命令失败并提示 profile 不存在 |
 
 ### 5. Good/Base/Bad Cases
 
@@ -505,7 +507,10 @@ updates:
 - `sing install` 的 PATH 解析、`--bin` 覆盖、找不到二进制失败。
 - `nssm.exe` 参数列表构造，不通过 shell 字符串执行。
 - `sing start <name>` 服务已运行时失败。
-- `sing restart <name>` 停止失败时不继续启动。
+- `sing restart` 停止失败时不继续启动。
+- `sing restart` 不接受 profile 名参数。
+- `sing restart` 使用 active 配置重启。
+- `sing restart` 没有 active 配置或 active 配置不存在时失败。
 - `state.json` 读写、active 更新和删除 active 配置失败。
 - 配置名称校验。
 - HTTP 下载失败、写入失败和更新成功路径。
diff --git a/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/check.jsonl b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/check.jsonl
new file mode 100644
index 0000000..e4911a1
--- /dev/null
+++ b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/check.jsonl
@@ -0,0 +1,4 @@
+{"file": ".trellis/spec/backend/index.md", "reason": "Verify backend command contract and docs remain consistent."}
+{"file": ".trellis/spec/backend/error-handling.md", "reason": "Verify restart errors remain explicit and user-facing failures are not swallowed."}
+{"file": ".trellis/spec/backend/quality-guidelines.md", "reason": "Verify test coverage and required quality commands."}
+{"file": ".trellis/spec/backend/logging-guidelines.md", "reason": "Verify CLI output remains concise and separated by success/error path."}
diff --git a/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/implement.jsonl b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/implement.jsonl
new file mode 100644
index 0000000..fc152bf
--- /dev/null
+++ b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/implement.jsonl
@@ -0,0 +1,4 @@
+{"file": ".trellis/spec/backend/index.md", "reason": "Backend command contract and project facts for CLI behavior changes."}
+{"file": ".trellis/spec/backend/error-handling.md", "reason": "CLI error behavior for service and profile state failures."}
+{"file": ".trellis/spec/backend/quality-guidelines.md", "reason": "Required tests and quality commands for Python CLI changes."}
+{"file": ".trellis/spec/backend/logging-guidelines.md", "reason": "stdout/stderr output expectations for CLI commands."}
diff --git a/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/prd.md b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/prd.md
new file mode 100644
index 0000000..397cff6
--- /dev/null
+++ b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/prd.md
@@ -0,0 +1,58 @@
+# Fix restart active config behavior
+
+## Goal
+
+`sing restart` must restart the Windows service with the currently active profile and must not accept a profile name argument.
+
+## What I already know
+
+- User requirement: `sing restart` does not need parameters.
+- User requirement: restart should use the current active configuration.
+- Current implementation defines `restart(name: str)` and reconfigures the service with the provided profile.
+- `README.md` and backend SPEC currently document `sing restart <name>`.
+- Current tests cover service and state helpers but do not cover the Typer command-level restart argument contract.
+
+## Requirements
+
+- Change the CLI command contract from `sing restart <name>` to `sing restart`.
+- `sing restart` must load the current state and require `state.active` to be set.
+- `sing restart` must require the active profile to still exist.
+- `sing restart` must require an installed `sing-box.exe` path.
+- `sing restart` must stop the service, configure NSSM with the active profile path, start the service, and keep `state.active` unchanged.
+- `sing start <name>` service-running error must point users to `sing restart`.
+- Update tests for the no-argument restart behavior.
+- Update README and SPEC command descriptions to match the corrected contract.
+
+## Acceptance Criteria
+
+- [x] `sing restart` succeeds with the current active profile.
+- [x] `sing restart <name>` is rejected by Typer as an unexpected argument.
+- [x] `sing restart` fails clearly when no active profile is recorded.
+- [x] `sing restart` fails clearly when the active profile is missing.
+- [x] Python lint, type-check, and tests pass.
+
+## Definition of Done
+
+- Tests added or updated for the command behavior.
+- `uv run ruff check src` passes.
+- `uv run ty check src` passes.
+- `uv run pytest` passes.
+- Docs and SPEC reflect the finished behavior without extra notes or process commentary.
+
+## Out of Scope
+
+- Backward compatibility for `sing restart <name>`.
+- Selecting or switching profiles during restart.
+- Changing `sing start`, `sing stop`, `sing update`, `sing remove`, or profile storage beyond the required help/error text updates.
+
+## Technical Notes
+
+- Relevant files inspected:
+  - `src/sing_cli/cli.py`
+  - `tests/test_service.py`
+  - `tests/test_state.py`
+  - `README.md`
+  - `.trellis/spec/backend/index.md`
+  - `.trellis/spec/backend/error-handling.md`
+  - `.trellis/spec/backend/quality-guidelines.md`
+  - `.trellis/spec/backend/logging-guidelines.md`
diff --git a/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/task.json b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/task.json
new file mode 100644
index 0000000..1d98715
--- /dev/null
+++ b/.trellis/tasks/archive/2026-05/05-12-fix-restart-active-config/task.json
@@ -0,0 +1,26 @@
+{
+  "id": "fix-restart-active-config",
+  "name": "fix-restart-active-config",
+  "title": "Fix restart active config behavior",
+  "description": "",
+  "status": "completed",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "pixelcola",
+  "assignee": "pixelcola",
+  "createdAt": "2026-05-12",
+  "completedAt": "2026-05-12",
+  "branch": null,
+  "base_branch": "main",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}
\ No newline at end of file
diff --git a/.trellis/workspace/pixelcola/index.md b/.trellis/workspace/pixelcola/index.md
index 6ac7de0..4108048 100644
--- a/.trellis/workspace/pixelcola/index.md
+++ b/.trellis/workspace/pixelcola/index.md
@@ -8,7 +8,7 @@
 
 <!-- @@@auto:current-status -->
 - **Active File**: `journal-1.md`
-- **Total Sessions**: 4
+- **Total Sessions**: 5
 - **Last Active**: 2026-05-12
 <!-- @@@/auto:current-status -->
 
@@ -19,7 +19,7 @@
 <!-- @@@auto:active-documents -->
 | File | Lines | Status |
 |------|-------|--------|
-| `journal-1.md` | ~139 | Active |
+| `journal-1.md` | ~172 | Active |
 <!-- @@@/auto:active-documents -->
 
 ---
@@ -29,6 +29,7 @@
 <!-- @@@auto:session-history -->
 | # | Date | Title | Commits | Branch |
 |---|------|-------|---------|--------|
+| 5 | 2026-05-12 | Fix restart active profile | `010e59e` | `fix/restart-active-config` |
 | 4 | 2026-05-12 | Fix Windows subprocess output decoding | `e90a676` | `fix/windows-subprocess-output-decoding` |
 | 3 | 2026-05-12 | Use NSSM for Windows service | `72c1b0d` | `fix/use-nssm-service` |
 | 2 | 2026-05-12 | Windows sing-box CLI | `2f18462` | `feature/windows-sing-box-cli` |
diff --git a/.trellis/workspace/pixelcola/journal-1.md b/.trellis/workspace/pixelcola/journal-1.md
index 6265149..c232414 100644
--- a/.trellis/workspace/pixelcola/journal-1.md
+++ b/.trellis/workspace/pixelcola/journal-1.md
@@ -137,3 +137,36 @@ Created PR #4 for the Windows subprocess decoding fix. Updated NSSM subprocess o
 ### Next Steps
 
 - None - task complete
+
+
+## Session 5: Fix restart active profile
+
+**Date**: 2026-05-12
+**Task**: Fix restart active profile
+**Branch**: `fix/restart-active-config`
+
+### Summary
+
+Changed sing restart to use the active profile without accepting a profile argument, updated docs/specs, added CLI regression tests, and opened PR #5.
+
+### Main Changes
+
+(Add details)
+
+### Git Commits
+
+| Hash | Message |
+|------|---------|
+| `010e59e` | (see git log) |
+
+### Testing
+
+- [OK] (Add test results)
+
+### Status
+
+[OK] **Completed**
+
+### Next Steps
+
+- None - task complete
diff --git a/README.md b/README.md
index 01d9510..bd9c6f0 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ Windows CLI for installing and controlling the `sing-box` Windows service.
 | `sing uninstall` | Delete the `sing-box` Windows service. |
 | `sing start <name>` | Start the service with a saved profile. |
 | `sing stop` | Stop the service. |
-| `sing restart <name>` | Stop, reconfigure, and start the service with a saved profile. |
+| `sing restart` | Stop, reconfigure, and start the service with the active profile. |
 | `sing add <name> <url>` | Download a complete `sing-box` JSON profile and save it under a name. |
 | `sing remove <name>` | Remove a saved non-active profile. |
 | `sing update <name>` | Redownload a saved profile from its URL. |
diff --git a/src/sing_cli/cli.py b/src/sing_cli/cli.py
index 545b9fa..abcfe6c 100644
--- a/src/sing_cli/cli.py
+++ b/src/sing_cli/cli.py
@@ -90,7 +90,7 @@ def start(name: str) -> None:
         entry = require_profile(state, name)
         bin_path = require_installed_bin(state)
         if service_is_running():
-            raise SingCliError(f"sing-box service is already running. Use 'sing restart {name}'.")
+            raise SingCliError("sing-box service is already running. Use 'sing restart'.")
         configure_service(bin_path, entry.path)
         start_service()
         state.active = name
@@ -110,19 +110,19 @@ def stop() -> None:
 
 
 @app.command()
-def restart(name: str) -> None:
+def restart() -> None:
     try:
         state = load_cli_state()
-        entry = require_profile(state, name)
+        if state.active is None:
+            raise SingCliError("No active profile. Run 'sing start <name>' first.")
+        entry = require_profile(state, state.active)
         bin_path = require_installed_bin(state)
         stop_service()
         configure_service(bin_path, entry.path)
         start_service()
-        state.active = name
-        save_cli_state(state)
     except SingCliError as error:
         fail(error)
-    typer.echo(f"Restarted {name}")
+    typer.echo(f"Restarted {state.active}")
 
 
 @app.command()
diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..c9bdb54
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,97 @@
+from pathlib import Path
+
+import pytest
+from typer.testing import CliRunner
+
+from sing_cli import cli
+from sing_cli.state import ProfileEntry, State, load_state, save_state
+
+
+def write_state(tmp_path: Path, state: State) -> None:
+    save_state(tmp_path / "state.json", state)
+
+
+def test_restart_uses_active_profile(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    runner = CliRunner()
+    calls: list[tuple[str, str | None, str | None]] = []
+    state = State(
+        bin="C:/tools/sing-box.exe",
+        active="home",
+        profiles={
+            "home": ProfileEntry(
+                url="https://example.com/home.json",
+                path="C:/profiles/home.json",
+                updated_at="2026-05-12T00:00:00Z",
+            )
+        },
+    )
+    write_state(tmp_path, state)
+    monkeypatch.setattr(cli, "app_dir", lambda: tmp_path)
+    monkeypatch.setattr(cli, "stop_service", lambda: calls.append(("stop", None, None)))
+    monkeypatch.setattr(
+        cli,
+        "configure_service",
+        lambda bin_path, profile_path: calls.append(("configure", bin_path, profile_path)),
+    )
+    monkeypatch.setattr(cli, "start_service", lambda: calls.append(("start", None, None)))
+
+    result = runner.invoke(cli.app, ["restart"])
+
+    assert result.exit_code == 0
+    assert result.stdout == "Restarted home\n"
+    assert calls == [
+        ("stop", None, None),
+        ("configure", "C:/tools/sing-box.exe", "C:/profiles/home.json"),
+        ("start", None, None),
+    ]
+    assert load_state(tmp_path / "state.json") == state
+
+
+def test_restart_rejects_profile_argument() -> None:
+    result = CliRunner().invoke(cli.app, ["restart", "home"])
+
+    assert result.exit_code != 0
+    assert "Got unexpected extra argument" in result.output
+
+
+def test_restart_requires_active_profile(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    write_state(tmp_path, State(bin="C:/tools/sing-box.exe"))
+    monkeypatch.setattr(cli, "app_dir", lambda: tmp_path)
+
+    result = CliRunner().invoke(cli.app, ["restart"])
+
+    assert result.exit_code == 1
+    assert result.stderr == "Error: No active profile. Run 'sing start <name>' first.\n"
+
+
+def test_restart_requires_existing_active_profile(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    write_state(tmp_path, State(bin="C:/tools/sing-box.exe", active="missing"))
+    monkeypatch.setattr(cli, "app_dir", lambda: tmp_path)
+
+    result = CliRunner().invoke(cli.app, ["restart"])
+
+    assert result.exit_code == 1
+    assert result.stderr == "Error: Profile does not exist: missing\n"
+
+
+def test_start_running_service_mentions_restart_without_name(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    write_state(
+        tmp_path,
+        State(
+            bin="C:/tools/sing-box.exe",
+            profiles={
+                "home": ProfileEntry(
+                    url="https://example.com/home.json",
+                    path="C:/profiles/home.json",
+                    updated_at="2026-05-12T00:00:00Z",
+                )
+            },
+        ),
+    )
+    monkeypatch.setattr(cli, "app_dir", lambda: tmp_path)
+    monkeypatch.setattr(cli, "service_is_running", lambda: True)
+
+    result = CliRunner().invoke(cli.app, ["start", "home"])
+
+    assert result.exit_code == 1
+    assert result.stderr == "Error: sing-box service is already running. Use 'sing restart'.\n"