---
title: "prefilter"
slug: "prefilter"
updated: 2026-02-06T06:01:12Z
published: 2026-02-06T06:01:12Z
canonical: "docs.fmad.io/prefilter"
---

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

# prefilter

Retrieval and modification of the [pre-capture filters](/v1/docs/fmadio-features-pre-capture-filter).

---

## /api/v1/capture/prefilter/get

Returns a JSON object containing the configurations of all pre-capture filters.

#### Address

`/api/v1/capture/prefilter/get`

#### Verb

GET

#### Arguments

This endpoint has no parameters.

#### Example

```bash
curl -u fmadio:xxx -s 'https://192.168.108.10/api/v1/capture/prefilter/get' | jq
{
  "Status": true,
  "Str": "[Thu Feb  5 07:46:46 2023] successfully fetched prefilter config",
  "Policy": "ACCEPT",
  "Slice": "64",
  "Config": {
    "prefilter0": {
      "enable": true,
      "action": "drop",
      "value": "all==true",
      "comment": ""
    },
    "prefilter1": {
      "enable": false,
      "action": "drop",
      "value": "",
      "comment": ""
    },
    # omitted for brevity...
    "prefilter15": {
      "enable": false,
      "action": "drop",
      "value": "",
      "comment": ""
    }
  }
}
```

---

## /api/v1/capture/prefilter/set

All-purpose configuration of a prefilter.

#### Address

`/api/v1/capture/prefilter/set`

#### Verb

GET

#### Arguments

| Parameter | Description |
| --- | --- |
| `Action` | Dictates what is done to the packet if it meets the condition set by the filter. Must be one of the following: - `accept` - `drop` - `slice` |
| `FilterId` | Which filter to alter. Can be either of the following: - `prefilter` followed by a whole number from 0 to 16 (e.g. `prefilter1`) - A whole number from 0 to 16 |
| `Enable` | Whether the filter should be active or inactive. Must be any of the following: - `enable` - `disable` - `true` - `false` |
| `Value` | The prefilter expression to use. |

#### Example

```bash
curl -u fmadio:xxx -Gs --data-urlencode 'FilterID=1' --data-urlencode 'Enable=true' --data-urlencode 'Value=all==true' --data-urlencode 'Action=drop' 'https://192.168.108.10/v1/capture/prefilter/set' | jq
{
  "Status": true,
  "Str": "[Fri Feb  6 15:26:57 2023] successfully updated"
}
```

---

## /api/v1/capture/prefilter/policy

Configures the default pre-filter policy (i.e. what happens to a packet that passes the filter’s expression).

#### Address

`/api/v1/capture/prefilter/policy`

#### Verb

GET

#### Arguments

| Parameter | Description |
| --- | --- |
| `Policy` | Must be one of the following: - `accept` - `drop` - `slice` |

#### Example

```bash
curl -u fmadio:xxx -Gs --data-urlencode 'Policy=accept' 'https://192.168.108.10/api/v1/capture/prefilter/policy' | jq
{
  "Status": true,
  "Str": "[Fri Feb  6 15:37:28 2023] successfully updated Policy to ACCEPT"
}
```

---

## /api/v1/capture/prefilter/slice

Configure how many bytes will be kept from the start of a packet if it passes a filter whose action is set to `slice`.

#### Address

`/api/v1/capture/prefilter/slice`

#### Verb

GET

#### Arguments

| Parameter | Description |
| --- | --- |
| `Slice` | The number of bytes kept from the start of a packet if it passes a filter whose action is set to `slice`. Must be 64, 128, or 256. |

#### Example

```bash
curl -u fmadio:xxx -Gs --data-urlencode 'Slice=128' 'https://192.168.108.10/api/v1/capture/prefilter/slice' | jq
{
  "Status": true,
  "Str": "[Fri Feb  6 15:35:00 2023] successfully updated slice to 128 Bytes"
}
```