diff --git a/README.md b/README.md
index e8212a5..0355fd4 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# FastAPI Throttle
+    # FastAPI Throttle
 
 [![PyPI](https://img.shields.io/pypi/v/fastapi-throttle?logo=pypi&label=PyPI)](https://pypi.org/project/fastapi-throttle/)
 [![CI](https://github.com/AliYmn/fastapi-throttle/actions/workflows/ci.yml/badge.svg)](https://github.com/AliYmn/fastapi-throttle/actions?query=workflow%3ACI)
@@ -64,6 +64,9 @@ async def root():
 - **Simple Configuration**: Just specify request count and time window
 - **Route-Level Control**: Apply different limits to different endpoints
 - **FastAPI Integration**: Works with FastAPI's dependency injection system
+- **Custom Keying (optional)**: Provide a `key_func(Request) -> str` to limit by user, API key, path, etc.
+- **Proxy-Aware (optional)**: `trust_proxy=True` to use `X-Forwarded-For` when behind proxies/CDNs
+- **Rate-Limit Headers (optional)**: Add `X-RateLimit-*` and `Retry-After` for clients
 
 ## Usage Examples
 
@@ -109,14 +112,67 @@ async def get_resource():
 app.include_router(router)
 ```
 
+### Custom Key Function (limit by user or path)
+
+```python
+from fastapi import FastAPI, Depends, Request
+from fastapi_throttle import RateLimiter
+
+app = FastAPI()
+
+def user_key(req: Request) -> str:
+    # Example: extract user-id from header or auth (for demo only)
+    return req.headers.get("x-user-id", req.client.host or "unknown")
+
+limiter = RateLimiter(times=10, seconds=60, key_func=user_key)
+
+@app.get("/data", dependencies=[Depends(limiter)])
+async def data():
+    return {"ok": True}
+```
+
+### Behind proxy/CDN (trust X-Forwarded-For)
+
+```python
+from fastapi import FastAPI, Depends
+from fastapi_throttle import RateLimiter
+
+app = FastAPI()
+
+proxy_limit = RateLimiter(times=5, seconds=30, trust_proxy=True)
+
+@app.get("/proxy", dependencies=[Depends(proxy_limit)])
+async def proxy_route():
+    return {"ok": True}
+```
+
+### Standard rate-limit headers
+
+```python
+from fastapi import FastAPI, Depends
+from fastapi_throttle import RateLimiter
+
+app = FastAPI()
+
+headers_limit = RateLimiter(times=5, seconds=60, add_headers=True)
+
+@app.get("/limited", dependencies=[Depends(headers_limit)])
+async def limited():
+    return {"message": "Check X-RateLimit-* headers"}
+```
+
 ## Configuration
 
-The `RateLimiter` class takes two parameters:
+The `RateLimiter` class parameters:
 
 | Parameter | Type | Description |
 |-----------|------|-------------|
 | `times`   | int  | Maximum number of requests allowed in the time window |
 | `seconds` | int  | Time window in seconds |
+| `detail`  | str  | Optional custom detail message for 429 responses |
+| `key_func` | `Callable[[Request], str]` | Optional custom function to compute the rate-limit key |
+| `trust_proxy` | bool | If True, tries `X-Forwarded-For` for client identification (default False) |
+| `add_headers` | bool | If True, adds `X-RateLimit-Limit`, `X-RateLimit-Remaining`, and `Retry-After` headers |
 
 ## How It Works
 
@@ -127,13 +183,17 @@ The rate limiter:
 4. Counts requests within the window
 5. Returns HTTP 429 when limit is exceeded
 
+## Notes
+
+- When `add_headers=True`, successful responses (2xx) include `X-RateLimit-Limit` and `X-RateLimit-Remaining`. On 429 responses, only `Retry-After` is included.
+- Use `trust_proxy=True` only when running behind a trusted proxy/load balancer that correctly sets `X-Forwarded-For`. The first IP is treated as the client.
+
 ## Limitations
 
 - **Memory Storage**: Data is lost when the application restarts
-- **Single-Server Only**: Not designed for distributed environments
-- **IP-Based Identification**: May not work well with shared IPs or proxies
+- **Single-Server Only**: Intended for monoliths/single-worker setups (in-memory, no cross-process sync)
+- **IP-Based Identification (default)**: With shared IPs/proxies, prefer `key_func` or `trust_proxy`
 - **Memory Usage**: Can grow with number of unique clients
-- **No Rate Limit Headers**: Doesn't include standard rate limit headers in responses
 
 ## When to Use
 
@@ -143,7 +203,7 @@ FastAPI Throttle is ideal for:
 - Projects where simplicity is valued over advanced features
 - Development and testing environments
 
-For high-traffic production applications or distributed systems, consider a Redis-based solution.
+For high-traffic production applications or distributed systems, prefer a distributed rate limiter (e.g., Redis-backed). This package intentionally avoids Redis and focuses on simplicity.
 
 ## Testing
 
@@ -160,9 +220,8 @@ pytest --cov=fastapi_throttle -q
 
 ## Roadmap
 
-- Add optional Redis backend for distributed environments
-- Optional standard rate-limit headers in responses
 - Middleware variant in addition to dependency-based limiter
+- (Maybe) Pluggable storage interface if a second backend is introduced later
 
 ## License
 
diff --git a/fastapi_throttle/limiter.py b/fastapi_throttle/limiter.py
index a382158..5d607ee 100644
--- a/fastapi_throttle/limiter.py
+++ b/fastapi_throttle/limiter.py
@@ -1,6 +1,6 @@
 import time
-from fastapi import Request, HTTPException
-from typing import Dict, List, Optional
+from fastapi import Request, HTTPException, Response
+from typing import Callable, Dict, List, Optional
 
 
 class RateLimiter:
@@ -13,11 +13,14 @@ class RateLimiter:
     Attributes:
         times (int): The maximum number of requests allowed per client within the specified period.
         seconds (int): The time window in seconds during which requests are counted.
-        requests (Dict[str, List[float]]): A dictionary storing request timestamps for each client IP.
+        requests (Dict[str, List[float]]): A dictionary storing request timestamps for each computed key.
         detail (str): The detail message to be returned to the client if the requests exceed the limit within the specified period.
+        key_func (Optional[Callable[[Request], str]]): Optional function to compute a custom rate-limit key.
+        trust_proxy (bool): When True, uses X-Forwarded-For to determine client IP (first hop).
+        add_headers (bool): When True, adds rate-limit headers to the response.
     """
 
-    def __init__(self, times: int, seconds: int, detail : Optional[str] = None) -> None:
+    def __init__(self, times: int, seconds: int, detail: Optional[str] = None, *, key_func: Optional[Callable[[Request], str]] = None, trust_proxy: bool = False, add_headers: bool = False) -> None:
         """
         Initializes the RateLimiter instance with the specified request limit and time period.
 
@@ -25,15 +28,20 @@ def __init__(self, times: int, seconds: int, detail : Optional[str] = None) -> N
             times (int): The maximum number of requests allowed per client.
             seconds (int): The time period in seconds for rate limiting.
             detail (str): The detail message to be returned to the client if rate limit is exceeded.
+            key_func (Callable[[Request], str], optional): Custom key function. Defaults to None (client IP based).
+            trust_proxy (bool): If True, attempts to use X-Forwarded-For header for client identification.
+            add_headers (bool): If True, attaches standard rate limit headers to the response.
         """
         self.times: int = times
         self.seconds: int = seconds
         self.requests: Dict[str, List[float]] = {}
-        self.detail: str = detail
-        if self.detail is None:
-            self.detail: str = "Too Many Requests"            
+        # Ensure non-None detail without violating typing
+        self.detail: str = detail or "Too Many Requests"
+        self.key_func: Optional[Callable[[Request], str]] = key_func
+        self.trust_proxy: bool = trust_proxy
+        self.add_headers: bool = add_headers
 
-    async def __call__(self, request: Request) -> None:
+    async def __call__(self, request: Request, response: Response) -> None:
         """
         Checks if the incoming request exceeds the allowed rate limit.
 
@@ -43,27 +51,60 @@ async def __call__(self, request: Request) -> None:
 
         Args:
             request (Request): The incoming HTTP request object.
+            response (Response): The outgoing HTTP response object.
 
         Raises:
             HTTPException: If the request rate limit is exceeded, a 429 status code is returned.
         """
-        client_ip: str = request.client.host
-        current_time: float = time.time()
+        client = request.client
+        # Compute key: custom key_func takes precedence
+        if self.key_func is not None:
+            try:
+                key: str = self.key_func(request)
+            except Exception:
+                # Fail-safe: do not break request handling if custom key function errors out
+                key = "unknown"
+        else:
+            # Default behavior: determine client IP, optionally trusting proxy headers
+            key = "unknown"
+            if self.trust_proxy:
+                xff = request.headers.get("x-forwarded-for")
+                if xff:
+                    # First IP in X-Forwarded-For is the original client
+                    key = xff.split(",")[0].strip() or key
+            if key == "unknown":
+                key = client.host if (client and getattr(client, "host", None)) else "unknown"
+        current_time: float = time.monotonic()
+        window_start: float = current_time - self.seconds
 
-        # Initialize the client's request history if not already present
-        if client_ip not in self.requests:
-            self.requests[client_ip] = []
+        # Get and prune timestamps inside the window
+        existing = self.requests.get(key, [])
+        filtered: List[float] = [ts for ts in existing if ts > window_start]
+        if not filtered:
+            # Small hygiene: if list becomes empty, drop the key to avoid empty buckets
+            if key in self.requests:
+                del self.requests[key]
+            current_count = 0
+        else:
+            self.requests[key] = filtered
+            current_count = len(filtered)
 
-        # Filter out timestamps that are outside of the rate limit period
-        self.requests[client_ip] = [
-            timestamp
-            for timestamp in self.requests[client_ip]
-            if timestamp > current_time - self.seconds
-        ]
-
-        # Check if the number of requests exceeds the allowed limit
-        if len(self.requests[client_ip]) >= self.times:
-            raise HTTPException(status_code=429, detail=self.detail)
+        if current_count >= self.times:
+            # Compute Retry-After: time until the oldest timestamp leaves the window
+            oldest = min(filtered) if filtered else current_time
+            retry_after = int(max(0.0, self.seconds - (current_time - oldest)))
+            headers = {"Retry-After": str(retry_after)} if retry_after > 0 else None
+            raise HTTPException(status_code=429, detail=self.detail, headers=headers)
 
         # Record the current request timestamp
-        self.requests[client_ip].append(current_time)
+        if filtered:
+            # Append to existing filtered list
+            self.requests[key].append(current_time)
+        else:
+            # Create a fresh list for this key
+            self.requests[key] = [current_time]
+
+        # Optionally attach standard rate limit headers
+        if self.add_headers:
+            response.headers["X-RateLimit-Limit"] = str(self.times)
+            response.headers["X-RateLimit-Remaining"] = str(max(0, self.times - len(self.requests[key])))
diff --git a/index.rst b/index.rst
index 03d324d..b195fdc 100644
--- a/index.rst
+++ b/index.rst
@@ -6,10 +6,13 @@
 `fastapi-throttle` is a simple in-memory rate limiter for FastAPI applications. This package allows you to control the number of requests a client can make to your API within a specified time window without relying on external dependencies like Redis. It is ideal for lightweight applications where simplicity and speed are paramount.
 
 ## Features
-- **Without Redis** : You don’t need to install or configure Redis.
+- **Without Redis** : You don’t need to install or configure Redis (monolith/single-worker focus).
 - **In-Memory Rate Limiting**: No external dependencies required. Keeps everything in memory for fast and simple rate limiting.
 - **Flexible Configuration**: Easily configure rate limits per route or globally.
 - **Python Version Support**: Compatible with Python 3.8 up to 3.12.
+- **Custom Keying (optional)**: Provide a key function to limit by user, API key, path, etc.
+- **Proxy-Aware (optional)**: `trust_proxy=True` to read `X-Forwarded-For` behind proxies/CDNs.
+- **Rate-Limit Headers (optional)**: Add `X-RateLimit-*` and `Retry-After` headers for clients.
 
 ## Installation
 
@@ -57,6 +60,14 @@ async def route2():
 ## Configuration
 - times: The maximum number of requests allowed per client within the specified period.
 - seconds: The time window in seconds within which the requests are counted.
+- detail: Optional custom detail message for 429 responses.
+- key_func: Optional callable `key_func(Request) -> str` to compute a custom key (e.g., user id).
+- trust_proxy: If True, use the first IP from `X-Forwarded-For` when present (default False).
+- add_headers: If True, add `X-RateLimit-Limit`, `X-RateLimit-Remaining`, and `Retry-After`.
+
+## Notes
+- When `add_headers=True`, successful responses (200 range) include `X-RateLimit-Limit` and `X-RateLimit-Remaining`. On 429, only `Retry-After` is added.
+- Use `trust_proxy=True` only when your app is behind a trusted proxy/load balancer that correctly sets `X-Forwarded-For`. The first IP is treated as the client.
 
 ## Example with Custom Configuration
 Here is an example where you use custom rate limiting per endpoint:
@@ -71,3 +82,50 @@ app = FastAPI()
 async def custom():
     return {"message": "This is a custom route with its own rate limit."}
 ```
+
+## Advanced Examples
+
+### Custom key function (limit by user or path)
+```python
+from fastapi import FastAPI, Depends, Request
+from fastapi_throttle import RateLimiter
+
+app = FastAPI()
+
+def user_key(req: Request) -> str:
+    return req.headers.get("x-user-id", req.client.host or "unknown")
+
+limiter = RateLimiter(times=10, seconds=60, key_func=user_key)
+
+@app.get("/data", dependencies=[Depends(limiter)])
+async def data():
+    return {"ok": True}
+```
+
+### Behind proxy/CDN (trust X-Forwarded-For)
+```python
+from fastapi import FastAPI, Depends
+from fastapi_throttle import RateLimiter
+
+app = FastAPI()
+
+proxy_limit = RateLimiter(times=5, seconds=30, trust_proxy=True)
+
+@app.get("/proxy", dependencies=[Depends(proxy_limit)])
+async def proxy_route():
+    return {"ok": True}
+```
+
+### Standard rate-limit headers
+```python
+from fastapi import FastAPI, Depends
+from fastapi_throttle import RateLimiter
+
+app = FastAPI()
+
+headers_limit = RateLimiter(times=5, seconds=60, add_headers=True)
+
+@app.get("/limited", dependencies=[Depends(headers_limit)])
+async def limited():
+    return {"message": "Check X-RateLimit-* headers"}
+```
diff --git a/requirements.txt b/requirements.txt
index 9f2525e..014e672 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,5 +1,5 @@
 fastapi==0.116.1
 uvicorn==0.33.0
 pytest==8.3.5
-pytest-cov==6.2.1
+pytest-cov==5.0.0
 httpx==0.28.1
diff --git a/setup.py b/setup.py
index 845dc8c..92f992a 100644
--- a/setup.py
+++ b/setup.py
@@ -10,7 +10,7 @@
 
 setup(
     name="fastapi-throttle",
-    version="0.1.7",
+    version="0.1.8",
     packages=find_packages(),
     install_requires=[
         "fastapi",
diff --git a/tests/test_limiter.py b/tests/test_limiter.py
index a53c28d..4ca79b0 100644
--- a/tests/test_limiter.py
+++ b/tests/test_limiter.py
@@ -43,3 +43,94 @@ async def route2():
 
     response = client.get("/route2")
     assert response.status_code == 200  # Limit should be reset
+
+
+def test_add_headers_and_retry_after():
+    app = FastAPI()
+
+    limiter = RateLimiter(times=2, seconds=5, add_headers=True)
+
+    @app.get("/limited", dependencies=[Depends(limiter)])
+    async def limited():
+        return {"ok": True}
+
+    client = TestClient(app)
+
+    # First request should include X-RateLimit headers
+    r1 = client.get("/limited")
+    assert r1.status_code == 200
+    assert r1.headers.get("X-RateLimit-Limit") == "2"
+    assert r1.headers.get("X-RateLimit-Remaining") == "1"
+
+    # Second request still 200, remaining becomes 0
+    r2 = client.get("/limited")
+    assert r2.status_code == 200
+    assert r2.headers.get("X-RateLimit-Limit") == "2"
+    assert r2.headers.get("X-RateLimit-Remaining") == "0"
+
+    # Third request should hit 429 and include Retry-After
+    r3 = client.get("/limited")
+    assert r3.status_code == 429
+    assert r3.headers.get("Retry-After") is not None
+    assert r3.headers["Retry-After"].isdigit()
+
+
+def test_retry_after_without_add_headers():
+    app = FastAPI()
+
+    limiter = RateLimiter(times=1, seconds=5, add_headers=False)
+
+    @app.get("/rl", dependencies=[Depends(limiter)])
+    async def rl():
+        return {"ok": True}
+
+    client = TestClient(app)
+    assert client.get("/rl").status_code == 200
+    r2 = client.get("/rl")
+    assert r2.status_code == 429
+    assert r2.headers.get("Retry-After") is not None
+
+
+def test_trust_proxy_uses_x_forwarded_for():
+    app = FastAPI()
+
+    limiter = RateLimiter(times=1, seconds=10, trust_proxy=True)
+
+    @app.get("/p", dependencies=[Depends(limiter)])
+    async def p():
+        return {"ok": True}
+
+    client = TestClient(app)
+
+    # Same client but with same first IP should hit the limit on second call
+    headers_a = {"X-Forwarded-For": "1.1.1.1, 2.2.2.2"}
+    assert client.get("/p", headers=headers_a).status_code == 200
+    assert client.get("/p", headers=headers_a).status_code == 429
+
+    # Different first IP should be treated as a different key
+    headers_b = {"X-Forwarded-For": "3.3.3.3, 4.4.4.4"}
+    assert client.get("/p", headers=headers_b).status_code == 200
+
+
+def test_custom_key_func_by_user():
+    app = FastAPI()
+
+    def user_key(req):
+        return req.headers.get("x-user-id", "anon")
+
+    limiter = RateLimiter(times=1, seconds=10, key_func=user_key)
+
+    @app.get("/u", dependencies=[Depends(limiter)])
+    async def u():
+        return {"ok": True}
+
+    client = TestClient(app)
+
+    # user A limited on second call
+    headers_a = {"x-user-id": "A"}
+    assert client.get("/u", headers=headers_a).status_code == 200
+    assert client.get("/u", headers=headers_a).status_code == 429
+
+    # user B is a different key, first call is allowed
+    headers_b = {"x-user-id": "B"}
+    assert client.get("/u", headers=headers_b).status_code == 200