---
title: "Action fastline"
description: "Searches the Fast Line knowledge base and generates an AI response."
---

# Action `fastline`

> **System ID:** `action_fastline`

## Description

**Fast Line:** searches for relevant question–answer pairs in the knowledge base (vector search) and generates an AI response from a prompt. The result is stored in a constant (`summarized` or `save_response`). If the best answer has an alias — the scenario can jump to the corresponding node.

## Events (scenario branches)

| Event | When it occurs |
|-------|----------------|
| **success** | Answers found, AI generated text |
| **not_found** | No suitable answers in the knowledge base |
| **error** | Missing input text, AI prompt/key, or generation error |

If the best answer’s **alias** fired and the node jump succeeded — there may be no named branch (the scenario goes to the alias).

## Parameters

| Parameter | Type | Required | Default | Description |
|-----------|------|----------|---------|-------------|
| `prompt` | string | yes | — | AI prompt template. Supports placeholders |
| `user_input` | string | no | `null` | User question; otherwise — `fastline_search_request` constant or message text |
| `bot_id` | string / number | no | current bot | Bot whose knowledge base to search |
| `provider` | string | no | `null` | AI provider |
| `model` | string | no | `null` | AI model |
| `apiKey` | string | no | `null` | Key (also `openai_token`) |
| `limit` | number | no | `null` | Maximum answer candidates |
| `max_distance` | number | no | `null` | Vector search distance threshold |
| `temperature` | number | no | `null` | AI temperature (0–2) |
| `max_tokens` | number | no | `500` | Response token limit |
| `top_p` | number | no | `1` | Top-p parameter |
| `user` | string | no | `null` | User identifier for AI |
| `question_fastline` | string | no | `null` | Overrides the user question |
| `save_response` | string | no | `"summarized"` | Constant for the AI response |
| `custom_fields` | object | no | `null` | Additional AI settings |

## Configuration example

```json
{
  "user_input": "{{user_question}}",
  "prompt": "Answer based on the context:\n{{answers}}\n\nQuestion: {{user_input}}",
  "limit": 5,
  "max_distance": 0.5,
  "save_response": "ai_answer"
}
```

## Related docs

- [Actions reference](/en/actionjail/reference/actions-reference.md)