> ## Documentation Index
> Fetch the complete documentation index at: https://docs.throttlr.yashjejurkar.me/llms.txt
> Use this file to discover all available pages before exploring further.

# Algorithms

> Understand the difference between Fixed Window and Sliding Window rate limiting.

## Fixed Window

The simplest algorithm. The time axis is split into fixed intervals (windows). Each window has its own counter that resets when the window expires.

```
Window 1 (0s–60s)        Window 2 (60s–120s)
│ req req req req req │   │ req req ...
│ count = 5           │   │ count = 1
└─────────────────────┘   └─────────────────
```

### Pros

* Simple to understand and implement
* Very fast — just `INCR` and `EXPIRE` in Redis
* Predictable — users know their quota resets every N seconds

### Cons

* **Boundary burst problem:** A user can make `2× limit` requests by hitting `limit` just before the window ends, then `limit` again at the start of the next window.

### When to use

* Login rate limiting (e.g. 5 attempts per minute)
* Email sending limits (e.g. 100 emails per hour)
* Simple API quotas

***

## Sliding Window

A more accurate approach. Instead of a fixed reset interval, the window slides continuously relative to the current time.

```
Now = T
Window = last 60 seconds = [T-60 ... T]

Only requests within this rolling window count.
```

### Pros

* No boundary burst problem
* Smooth, accurate limiting
* Better user experience for high-frequency APIs

### Cons

* Slightly more complex to implement
* Uses more Redis memory (stores request timestamps)

### When to use

* API endpoints where burst attacks matter
* Real-time systems (e.g. webhook deliveries, AI completions)
* High-traffic endpoints

***

## Comparison

|                     |  Fixed Window |  Sliding Window |
| ------------------- | :-----------: | :-------------: |
| Reset behavior      |   Hard reset  |     Rolling     |
| Burst vulnerability |      Yes      |        No       |
| Redis complexity    |      Low      |      Medium     |
| Best for            | Simple limits | Accurate limits |

***

## Choosing in the Dashboard

When creating a rule, select the algorithm from the dropdown:

* **FIXED\_WINDOW** — Simple, fast, good default
* **SLIDING\_WINDOW** — More accurate, better for security-sensitive routes