diff --git a/document-parser/infra/rate_limiter.py b/document-parser/infra/rate_limiter.py
new file mode 100644
index 0000000..bb82ee7
--- /dev/null
+++ b/document-parser/infra/rate_limiter.py
@@ -0,0 +1,89 @@
+"""Lightweight in-memory rate limiter middleware for FastAPI.
+
+Uses a sliding-window counter per client IP. No external dependency
+required — suitable for single-process deployments with SQLite.
+
+For multi-process or distributed setups, replace with a Redis-backed
+solution (e.g. slowapi).
+"""
+
+from __future__ import annotations
+
+import logging
+import time
+from collections import defaultdict
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING
+
+from starlette.middleware.base import BaseHTTPMiddleware, RequestResponseEndpoint
+from starlette.responses import JSONResponse, Response
+
+if TYPE_CHECKING:
+    from starlette.requests import Request
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class _ClientBucket:
+    """Sliding window of request timestamps for a single client."""
+
+    timestamps: list[float] = field(default_factory=list)
+
+    def count_recent(self, window: float, now: float) -> int:
+        """Remove expired entries and return the count of recent requests."""
+        cutoff = now - window
+        self.timestamps = [t for t in self.timestamps if t > cutoff]
+        return len(self.timestamps)
+
+    def add(self, now: float) -> None:
+        self.timestamps.append(now)
+
+
+class RateLimiterMiddleware(BaseHTTPMiddleware):
+    """Per-IP rate limiter using in-memory sliding windows.
+
+    Args:
+        app: The ASGI application.
+        requests_per_window: Max requests allowed per window.
+        window_seconds: Size of the sliding window in seconds.
+        exclude_paths: Paths exempt from rate limiting (e.g. health checks).
+    """
+
+    def __init__(
+        self,
+        app,
+        *,
+        requests_per_window: int = 60,
+        window_seconds: float = 60.0,
+        exclude_paths: tuple[str, ...] = ("/api/health",),
+    ):
+        super().__init__(app)
+        self._max_requests = requests_per_window
+        self._window = window_seconds
+        self._exclude = exclude_paths
+        self._buckets: dict[str, _ClientBucket] = defaultdict(_ClientBucket)
+
+    async def dispatch(self, request: Request, call_next: RequestResponseEndpoint) -> Response:
+        if request.url.path in self._exclude:
+            return await call_next(request)
+
+        client_ip = request.client.host if request.client else "unknown"
+        now = time.monotonic()
+
+        bucket = self._buckets[client_ip]
+        recent = bucket.count_recent(self._window, now)
+
+        if recent >= self._max_requests:
+            retry_after = int(self._window)
+            logger.warning(
+                "Rate limit exceeded for %s (%d/%d)", client_ip, recent, self._max_requests
+            )
+            return JSONResponse(
+                status_code=429,
+                content={"detail": "Too many requests"},
+                headers={"Retry-After": str(retry_after)},
+            )
+
+        bucket.add(now)
+        return await call_next(request)
diff --git a/document-parser/main.py b/document-parser/main.py
index 91955f6..654c88e 100644
--- a/document-parser/main.py
+++ b/document-parser/main.py
@@ -20,6 +20,7 @@ from fastapi.middleware.cors import CORSMiddleware
 
 from api.analyses import router as analyses_router
 from api.documents import router as documents_router
+from infra.rate_limiter import RateLimiterMiddleware
 from infra.settings import settings
 from persistence.database import get_connection, init_db
 from services.analysis_service import AnalysisService
@@ -94,6 +95,7 @@ app.add_middleware(
     allow_methods=["GET", "POST", "DELETE", "OPTIONS"],
     allow_headers=["Content-Type", "Authorization"],
 )
+app.add_middleware(RateLimiterMiddleware, requests_per_window=100, window_seconds=60)
 
 app.include_router(documents_router)
 app.include_router(analyses_router)
diff --git a/document-parser/tests/test_rate_limiter.py b/document-parser/tests/test_rate_limiter.py
new file mode 100644
index 0000000..82c7fc5
--- /dev/null
+++ b/document-parser/tests/test_rate_limiter.py
@@ -0,0 +1,93 @@
+"""Tests for the in-memory rate limiter middleware."""
+
+from __future__ import annotations
+
+from unittest.mock import patch
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+from infra.rate_limiter import RateLimiterMiddleware, _ClientBucket
+
+
+class TestClientBucket:
+    def test_count_recent_filters_old_entries(self):
+        bucket = _ClientBucket(timestamps=[1.0, 2.0, 3.0, 10.0])
+        count = bucket.count_recent(window=5.0, now=12.0)
+        assert count == 1  # only 10.0 is within [7.0, 12.0]
+
+    def test_count_recent_keeps_all_when_within_window(self):
+        bucket = _ClientBucket(timestamps=[10.0, 11.0, 12.0])
+        count = bucket.count_recent(window=60.0, now=15.0)
+        assert count == 3
+
+    def test_add(self):
+        bucket = _ClientBucket()
+        bucket.add(1.0)
+        bucket.add(2.0)
+        assert len(bucket.timestamps) == 2
+
+
+@pytest.fixture
+def limited_app():
+    """FastAPI app with a very low rate limit for testing."""
+    app = FastAPI()
+    app.add_middleware(
+        RateLimiterMiddleware,
+        requests_per_window=3,
+        window_seconds=60,
+        exclude_paths=("/health",),
+    )
+
+    @app.get("/test")
+    def test_endpoint():
+        return {"ok": True}
+
+    @app.get("/health")
+    def health():
+        return {"status": "ok"}
+
+    return app
+
+
+@pytest.fixture
+def client(limited_app):
+    return TestClient(limited_app)
+
+
+class TestRateLimiterMiddleware:
+    def test_allows_requests_under_limit(self, client):
+        for _ in range(3):
+            resp = client.get("/test")
+            assert resp.status_code == 200
+
+    def test_blocks_requests_over_limit(self, client):
+        for _ in range(3):
+            client.get("/test")
+
+        resp = client.get("/test")
+        assert resp.status_code == 429
+        assert resp.json()["detail"] == "Too many requests"
+        assert "Retry-After" in resp.headers
+
+    def test_health_excluded_from_limit(self, client):
+        # Exhaust the limit
+        for _ in range(3):
+            client.get("/test")
+
+        # Health should still work
+        resp = client.get("/health")
+        assert resp.status_code == 200
+
+    def test_window_resets(self, client):
+        """After the window expires, requests should be allowed again."""
+        for _ in range(3):
+            client.get("/test")
+
+        assert client.get("/test").status_code == 429
+
+        # Simulate time passing beyond the window
+        with patch("time.monotonic", return_value=1e12):
+            resp = client.get("/test")
+            assert resp.status_code == 200