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

# Agents

> Configuring the brain of your voice application

Agents are the core entity in Butter AI. An agent defines *who* is speaking, *how* they speak, and *what* they know. You can **sculpt your perfect agent** by mixing and matching providers.

## Configuration Components

An agent configuration consists of several key layers:

### 1. Transcriber (STT)

Converts user speech to text.

* **Providers**: Deepgram (Flux, Nova 3, Nova 2), ElevenLabs (Realtime Scribe v2, Scribe v1), Cartesia Ink Whisper, AWS Transcribe.
* **Selection**: Deepgram Nova 3 and Flux are generally recommended for the lowest latency and highest accuracy.

### 2. Intelligence (LLM)

The "brain" that decides what to say.

* **Providers**: OpenAI, Groq, Google Gemini, Cerebras, Amazon Bedrock.
* **Models**: Options range from Gemini 2.5 Flash Lite for high speed to Claude Sonnet 4 and Llama 4 Maverick for advanced reasoning.
* **Fallback Models**: You can configure a fallback LLM provider and model (e.g., `llm_fallback_provider` and `llm_fallback_model`) to ensure high availability if the primary provider fails.
* **System Prompt**: This is the most critical part. It defines the persona, guardrails, and instructions.
* **Temperature**: Controls creativity. Lower (0.3) is better for strict tasks; higher (0.7-0.9) is better for casual conversation.

### 3. Synthesizer (TTS)

Converts text back to audio.

* **Providers**: ElevenLabs, Cartesia, Amazon Polly (Neural and Generative).
* **Voice ID**: The specific voice persona to use (e.g., "Clyde" from ElevenLabs, "Brooke" from Cartesia).

### 4. Language

Sets the primary language for the agent (e.g., English), dictating which models and voices apply natively to interactions.

## Capabilities

### Speak First

If `speak_first` is set to `true`, the agent will initiate the conversation immediately upon connection. If `false`, it waits for the user to speak.

### End Call Tool

Agents can be permitted to programmatically hang up the call when tasks are complete by enabling the `end_call_tool` flag.

### Voicemail Detection

If enabled, the system uses Answering Machine Detection (AMD) to determine if a human or voicemail picked up.

* **Voicemail Message**: Specific message to leave if a machine is detected.
* **Delay**: Wait time before speaking to ensure the beep has passed.

### Recording

Call recording can be toggled on/off. Recordings are stored in S3 and accessible via the API.

## Tools and Knowledge

Agents can be augmented with:

* **[Knowledge Base](/concepts/knowledge-base)**: Passive knowledge (RAG) powered by Pinecone. Attach valid `kb_document_ids` directly to the agent.
* **[Tools](/concepts/tools)**: Active capabilities (API calls) attached via `custom_tools`.