# CF.ADDNX

```json metadata
{
  "title": "CF.ADDNX",
  "description": "Adds an item to a Cuckoo Filter if the item did not exist previously.",
  "categories": ["docs","develop","stack","oss","rs","rc","oss","kubernetes","clients"],
  "arguments": [{"name":"key","type":"key"},{"name":"item","type":"string"}],
  "syntax_fmt": "CF.ADDNX key item",
  "complexity": "O(k + i), where k is the number of sub-filters and i is maxIterations",
  "group": "cf",
  "acl_categories": ["@cuckoo","@write","@slow"],
  "since": "1.0.0",
  "tableOfContents": {"sections":[{"id":"required-arguments","title":"Required arguments"},{"id":"examples","title":"Examples"},{"id":"redis-enterprise-and-redis-cloud-compatibility","title":"Redis Enterprise and Redis Cloud compatibility"},{"id":"return-information","title":"Return information"}]}
}
```













Adds an item to a cuckoo filter if the item does not exist.

This command is similar to the combination of [`CF.EXISTS`](https://redis.io/docs/latestcommands/cf.exists/) and [`CF.ADD`](https://redis.io/docs/latestcommands/cf.add/). It does not add an item into the filter if its fingerprint already exists.

<note><b>Notes:</b>

- This command is slower than [`CF.ADD`](https://redis.io/docs/latestcommands/cf.add/) because it first checks whether the item exists.
- Since [`CF.EXISTS`](https://redis.io/docs/latestcommands/cf.exists/) can result in false positive, `CF.ADDNX` may not add an item because it is supposedly already exist, which may be wrong.

</note>

## Required arguments

<details open><summary><code>key</code></summary>

is key name for a cuckoo filter to add items to.

If `key` does not exist - a new cuckoo filter is created.
</details>

<details open><summary><code>item</code></summary>

is an item to add.
</details>

## Examples


redis> CF.ADDNX cf item
(integer) 1
redis> CF.ADDNX cf item
(integer) 0


## Redis Enterprise and Redis Cloud compatibility

| Redis<br />Enterprise | Redis<br />Cloud | <span style="min-width: 9em; display: table-cell">Notes</span> |
|:----------------------|:-----------------|:------|
| <span title="Supported">&#x2705; Supported</span><br /> | <span title="Supported">&#x2705; Flexible & Annual</span><br /><span title="Supported">&#x2705; Free & Fixed</nobr></span> |  |

## Return information

{{< multitabs id="cf-addnx-return-info" 
    tab1="RESP2" 
    tab2="RESP3" >}}

One of the following:
* [Integer reply](https://redis.io/docs/latest/develop/reference/protocol-spec#integers): `1` for successfully adding an item to the filter or `0` if the item's fingerprint already exists in the filter.
* [Simple error reply](https://redis.io/docs/latest/develop/reference/protocol-spec#simple-errors) in these cases: invalid arguments, wrong key type, or when the filter is full.

-tab-sep-

One of the following:
* [Boolean reply](https://redis.io/docs/latest/develop/reference/protocol-spec#booleans): `true` for successfully adding an item to the filter or `false` if the item's fingerprint already exists in the filter.
* [Simple error reply](https://redis.io/docs/latest/develop/reference/protocol-spec#simple-errors) in these cases: invalid arguments, wrong key type, or when the filter is full.