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

# PFADD

> Add elements to HyperLogLog.

Use `PFADD` to add elements to a HyperLogLog.

A HyperLogLog estimates how many distinct items it has seen while using a small, fixed amount of memory (at most about 12 KB) no matter how many elements pass through it. That is the trade it makes: individual elements are not stored, so they cannot be listed, checked for membership, or removed, and the cardinality that comes back from [`PFCOUNT`](/docs/redis/commands/hyperloglog/pfcount) is an approximation with a standard error of about 0.81%.

The key is created on first use, and the reply is `1` when the internal registers changed as a result of the call, which is a hint that at least one element was new, and `0` when they did not. Calling `PFADD` with no elements creates an empty HyperLogLog if the key does not exist yet. Use it for counts where the exact number does not matter, such as unique visitors per page or per day, and a set for cases where you must be able to look elements up.

## Syntax

```redis theme={"system"}
PFADD <key> [<element> [<element> ...]]
```

## Arguments

| Argument    | Required | Repeatable | Description                        |
| ----------- | -------- | ---------- | ---------------------------------- |
| `<key>`     | Yes      | No         | Redis key targeted by the command. |
| `<element>` | No       | Yes        | Element to add to the HyperLogLog. |

## Response

The reply reports the result of the operation. Error replies have the same shape in RESP2 and RESP3 and are surfaced as exceptions by the SDKs below.

| Protocol | Reply                                                                     |
| -------- | ------------------------------------------------------------------------- |
| RESP2    | Integer: `1` if at least one internal register was altered, `0` otherwise |
| RESP3    | Integer: `1` if at least one internal register was altered, `0` otherwise |

<Note>
  Client libraries often decode bulk strings, maps, sets, and numeric strings into language-native values. The table describes the Redis wire reply.
</Note>

## Examples

TCP examples use the TLS `REDIS_URL` from the Upstash console. REST examples use `UPSTASH_REDIS_REST_URL` and `UPSTASH_REDIS_REST_TOKEN`.

<AccordionGroup>
  <Accordion title="Redis CLI" icon="terminal">
    ```bash theme={"system"}
    PFADD my-key element
    ```
  </Accordion>

  <Accordion title="@upstash/redis" icon="node-js" iconType="brands">
    ```ts theme={"system"}
    import { Redis } from "@upstash/redis";

    const redis = Redis.fromEnv();
    const result = await redis.pfadd("my-key", "element");
    console.log(result);
    ```
  </Accordion>

  <Accordion title="upstash_redis" icon="python" iconType="brands">
    ```python theme={"system"}
    from upstash_redis import Redis

    redis = Redis.from_env()
    result = redis.pfadd("my-key", "member")
    print(result)
    ```
  </Accordion>

  <Accordion title="ioredis" icon="node-js" iconType="brands">
    ```ts theme={"system"}
    import Redis from "ioredis";

    const redis = new Redis(process.env.REDIS_URL!);
    const result = await redis.pfadd("my-key", "element");
    console.log(result);
    ```
  </Accordion>

  <Accordion title="node-redis" icon="node-js" iconType="brands">
    ```ts theme={"system"}
    import { createClient } from "redis";

    const client = await createClient({ url: process.env.REDIS_URL })
      .on("error", console.error)
      .connect();
    const result = await client.pfAdd("my-key", "element");
    console.log(result);
    ```
  </Accordion>

  <Accordion title="redis-py" icon="python" iconType="brands">
    ```python theme={"system"}
    import os
    import redis

    client = redis.from_url(os.environ["REDIS_URL"])
    result = client.pfadd("my-key", "member")
    print(result)
    ```
  </Accordion>

  <Accordion title="go-redis" icon="golang" iconType="brands">
    ```go theme={"system"}
    package main

    import (
        "context"
        "fmt"
        "os"

        "github.com/redis/go-redis/v9"
    )

    func main() {
        opts, err := redis.ParseURL(os.Getenv("REDIS_URL"))
        if err != nil {
            panic(err)
        }
        client := redis.NewClient(opts)
        result, err := client.PFAdd(context.Background(), "my-key").Result()
        if err != nil {
            panic(err)
        }
        fmt.Println(result)
    }
    ```
  </Accordion>

  <Accordion title="jedis" icon="java" iconType="brands">
    ```java theme={"system"}
    import java.net.URI;

    import redis.clients.jedis.Jedis;

    try (Jedis jedis = new Jedis(new URI(System.getenv("REDIS_URL")))) {
      Object result = jedis.pfadd("my-key");
      System.out.println(result);
    }
    ```
  </Accordion>

  <Accordion title="redis-rs" icon="rust" iconType="brands">
    ```rust theme={"system"}
    use redis::TypedCommands;

    fn main() -> redis::RedisResult<()> {
        let url = std::env::var("REDIS_URL").expect("REDIS_URL is not set");
        let client = redis::Client::open(url)?;
        let mut connection = client.get_connection()?;

        let result = connection.pfadd("my-key", &["member"])?;
        println!("{result:?}");
        Ok(())
    }
    ```
  </Accordion>
</AccordionGroup>