# WATCH

> Watch keys for changes.

Use `WATCH` to mark keys whose modification should cancel the next transaction, which gives you optimistic locking.

If any watched key is changed by another client between the `WATCH` and the [`EXEC`](/redis/commands/transactions/exec), the transaction is not executed and `EXEC` replies with null instead. Nothing is locked in the meantime: other clients keep working normally, and the conflict is detected rather than prevented.

The usual loop is: watch the keys, read them, decide what to write, open [`MULTI`](/redis/commands/transactions/multi), queue the writes, and call `EXEC`, retrying from the top when the reply is null. That is how a read-modify-write cycle stays correct without holding a lock. All watches are cleared by `EXEC` and [`DISCARD`](/redis/commands/transactions/discard).

The raw command is TCP-only. Over HTTP, use the transaction or pipeline API of an Upstash SDK instead of sending this command directly.

## Syntax

```redis
WATCH <key> [<key> ...]
```

## Arguments

| Argument | Required | Repeatable | Description |
| --- | --- | --- | --- |
| `<key>` | Yes | Yes | Redis key targeted by the command. |

## Important points

- The raw command is TCP-only. For HTTP, use an Upstash SDK transaction API rather than sending this command directly.

## 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 | Simple string `OK` |
| RESP3 | Simple string `OK` |

<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
WATCH balance
```

</Accordion>

<Accordion title="ioredis" icon="node-js" iconType="brands">

```ts
import Redis from "ioredis";

const client = new Redis(process.env.REDIS_URL!);
await client.watch("balance");
const result = await client.multi().set("balance", "100").exec();
```

</Accordion>

<Accordion title="node-redis" icon="node-js" iconType="brands">

```ts
import { createClient } from "redis";

const client = await createClient({ url: process.env.REDIS_URL }).connect();
await client.watch("balance");
const result = await client.multi().set("balance", "100").exec();
```

</Accordion>

<Accordion title="redis-py" icon="python" iconType="brands">

```python
import os
import redis

client = redis.from_url(os.environ["REDIS_URL"])
with client.pipeline() as pipe:
    pipe.watch("balance")
    pipe.multi()
    pipe.set("balance", "100")
    result = pipe.execute()
```

</Accordion>

<Accordion title="go-redis" icon="golang" iconType="brands">

```go
ctx := context.Background()
opts, err := redis.ParseURL(os.Getenv("REDIS_URL"))
if err != nil { panic(err) }
client := redis.NewClient(opts)

err = client.Watch(ctx, func(tx *redis.Tx) error {
    _, err := tx.TxPipelined(ctx, func(pipe redis.Pipeliner) error {
        pipe.Set(ctx, "balance", "100", 0)
        return nil
    })
    return err
}, "balance")
if err != nil { panic(err) }
```

</Accordion>

<Accordion title="jedis" icon="java" iconType="brands">

```java
import java.net.URI;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.Transaction;

try (Jedis jedis = new Jedis(new URI(System.getenv("REDIS_URL")))) {
  jedis.watch("balance");
  try (Transaction transaction = jedis.multi()) {
    transaction.set("balance", "100");
    Object result = transaction.exec();
  }
}
```

</Accordion>

<Accordion title="redis-rs" icon="rust" iconType="brands">

```rust
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 _: () = redis::transaction(&mut connection, &["balance"], |con, pipe| {
        pipe.set("balance", "100").ignore().query::<Option<()>>(con)
    })?;
    Ok(())
}
```

</Accordion>

</AccordionGroup>