diff --git a/ai-converter/Dockerfile b/ai-converter/Dockerfile
index 70b4c21..a009c29 100644
--- a/ai-converter/Dockerfile
+++ b/ai-converter/Dockerfile
@@ -4,13 +4,11 @@ FROM python:3.12-slim
 
 WORKDIR /app
 
-COPY requirements.txt ./
-RUN pip install --no-cache-dir -r requirements.txt \
-    && useradd --system --no-create-home converter
+RUN useradd --system --no-create-home converter
 
 COPY app.py ./
 USER converter
 
 EXPOSE 8090
 
-CMD ["uvicorn", "app:app", "--host", "0.0.0.0", "--port", "8090"]
+CMD ["python", "app.py"]
diff --git a/ai-converter/app.py b/ai-converter/app.py
index 0bd4ff6..05cf9bd 100644
--- a/ai-converter/app.py
+++ b/ai-converter/app.py
@@ -7,17 +7,15 @@ features that would otherwise produce a silently corrupted AI document.
 
 from __future__ import annotations
 
+import json
 import math
 import re
 from datetime import datetime, timezone
+from http import HTTPStatus
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 from typing import Iterable
 from xml.etree import ElementTree as ET
 
-from fastapi import FastAPI, HTTPException, Request
-from fastapi.responses import Response
-
-app = FastAPI(title="WordCloud AI Converter", version="0.1.0")
-
 MAX_SVG_BYTES = 25 * 1024 * 1024
 SVG_NS = "{http://www.w3.org/2000/svg}"
 NUMBER = r"[-+]?(?:\d*\.\d+|\d+\.?)(?:[eE][-+]?\d+)?"
@@ -25,36 +23,83 @@ PATH_TOKENS = re.compile(rf"[AaCcHhLlMmQqSsTtVvZz]|{NUMBER}")
 TRANSFORM = re.compile(rf"([A-Za-z]+)\s*\(([^)]*)\)")
 
 
-@app.get("/health")
-def health() -> dict[str, str]:
-    return {"status": "ok"}
-
-
-@app.post("/convert")
-async def convert(request: Request) -> Response:
-    raw = await request.body()
+def convert_svg(raw: bytes) -> bytes:
     if not raw:
-        raise HTTPException(status_code=400, detail="SVG 内容不能为空")
+        raise RequestError(HTTPStatus.BAD_REQUEST, "SVG 内容不能为空")
     if len(raw) > MAX_SVG_BYTES:
-        raise HTTPException(status_code=413, detail="SVG 文件超过 25 MB 限制")
+        raise RequestError(HTTPStatus.REQUEST_ENTITY_TOO_LARGE, "SVG 文件超过 25 MB 限制")
     if b"<!DOCTYPE" in raw.upper() or b"<!ENTITY" in raw.upper():
-        raise HTTPException(status_code=400, detail="不支持包含 DTD 或实体的 SVG")
+        raise RequestError(HTTPStatus.BAD_REQUEST, "不支持包含 DTD 或实体的 SVG")
 
     try:
         root = ET.fromstring(raw)
         ai = svg_to_ai(root)
     except UnsupportedSvg as exc:
-        raise HTTPException(status_code=422, detail=str(exc)) from exc
+        raise RequestError(HTTPStatus.UNPROCESSABLE_ENTITY, str(exc)) from exc
     except (ET.ParseError, ValueError) as exc:
-        raise HTTPException(status_code=400, detail=f"SVG 解析失败: {exc}") from exc
-
-    return Response(
-        content=ai.encode("ascii"),
-        media_type="application/postscript",
-        headers={"Content-Disposition": 'attachment; filename="wordcloud.ai"'},
-    )
+        raise RequestError(HTTPStatus.BAD_REQUEST, f"SVG 解析失败: {exc}") from exc
+    return ai.encode("ascii")
 
 
+class RequestError(ValueError):
+    def __init__(self, status: HTTPStatus, detail: str):
+        self.status = status
+        self.detail = detail
+        super().__init__(detail)
+
+
+class ConverterHandler(BaseHTTPRequestHandler):
+    server_version = "WordCloudAIConverter/0.1"
+
+    def do_GET(self) -> None:
+        if self.path == "/health":
+            self.send_bytes(HTTPStatus.OK, b'{"status":"ok"}', "application/json")
+            return
+        self.send_error(HTTPStatus.NOT_FOUND)
+
+    def do_POST(self) -> None:
+        if self.path != "/convert":
+            self.send_error(HTTPStatus.NOT_FOUND)
+            return
+        try:
+            length = int(self.headers.get("Content-Length", ""))
+            if length < 0:
+                raise ValueError
+        except ValueError:
+            self.send_json_error(HTTPStatus.BAD_REQUEST, "缺少或无效 Content-Length")
+            return
+        if length > MAX_SVG_BYTES:
+            self.send_json_error(HTTPStatus.REQUEST_ENTITY_TOO_LARGE, "SVG 文件超过 25 MB 限制")
+            return
+        raw = self.rfile.read(length)
+        try:
+            ai = convert_svg(raw)
+        except RequestError as exc:
+            self.send_json_error(exc.status, exc.detail)
+            return
+        self.send_bytes(
+            HTTPStatus.OK,
+            ai,
+            "application/postscript",
+            {"Content-Disposition": 'attachment; filename="wordcloud.ai"'},
+        )
+
+    def send_json_error(self, status: HTTPStatus, detail: str) -> None:
+        body = json.dumps({"detail": detail}, ensure_ascii=False).encode("utf-8")
+        self.send_bytes(status, body, "application/json; charset=utf-8")
+
+    def send_bytes(self, status: HTTPStatus, body: bytes, content_type: str, headers: dict[str, str] | None = None) -> None:
+        self.send_response(status)
+        self.send_header("Content-Type", content_type)
+        self.send_header("Content-Length", str(len(body)))
+        for key, value in (headers or {}).items():
+            self.send_header(key, value)
+        self.end_headers()
+        self.wfile.write(body)
+
+    def log_message(self, _format: str, *_args: object) -> None:
+        # The reverse proxy already logs requests; avoid echoing SVG payloads.
+        return
 class UnsupportedSvg(ValueError):
     pass
 
@@ -410,3 +455,7 @@ def format_number(value: float) -> str:
 
 def n(value: float) -> str:
     return format_number(value)
+
+
+if __name__ == "__main__":
+    ThreadingHTTPServer(("0.0.0.0", 8090), ConverterHandler).serve_forever()
diff --git a/ai-converter/requirements.txt b/ai-converter/requirements.txt
deleted file mode 100644
index a4c245d..0000000
--- a/ai-converter/requirements.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-fastapi>=0.115,<1
-uvicorn[standard]>=0.30,<1