> ## Documentation Index > Fetch the complete documentation index at: https://docs.zeroruntime.ai/llms.txt > Use this file to discover all available pages before exploring further. # Why Zero Runtime > How Zero Runtime compares to voice frameworks and no-code platforms (real code with your own providers, no infrastructure to run) and how it works under the hood. Zero Runtime is a runtime, not a framework. With a framework, you write the code *and* run the servers and GPUs, and manage latency yourself. With a runtime, you write the code and we run the rest. You write the agent; Zero Runtime runs it in real time and handles the hard part. It is serverless for voice AI agents. That puts it between two common options. Self-hosted frameworks give you full control, but you have to run the real-time infrastructure. No-code platforms run that for you, but lock you into a dashboard. Zero Runtime gives you the control of a framework with the ease of a managed platform: real code and your own providers, with nothing to operate. | | Self-hosted frameworks | No-code platforms | Zero Runtime | | ------------------------------------ | :--------------------: | :---------------: | :----------: | | Write real code and custom tools | Yes | No (dashboard) | Yes | | Operate media servers, GPUs, scaling | You do | Managed | Managed | | Swap any STT, LLM, or TTS provider | Yes | Limited | Yes | | Low-latency speech-to-speech | You tune it | Managed | Managed | ## What you get Agents are ordinary Python, TypeScript, or Go. Your logic and tools run in your own process, so you can use your existing libraries, data, and services. Each pipeline stage is a provider you choose. Swap any provider in a single line. Transport, GPUs, turn-taking, and autoscaling run on the runtime. You deploy a worker, not a cluster. Concepts and behavior match across Python, JavaScript, and Go. ## How it works A Zero Runtime agent has two halves: * **The agent** is your code: the instructions, logic, and tools you write. * **The runtime** is everything real-time that we run for you: streaming the audio, the GPUs, and the latency of the conversation. Your code runs in your process. The runtime runs on ours. ### Building blocks Every agent uses the same three pieces, named the same way in each SDK. Holds your behavior: the instructions, plus `on_enter` and `on_exit` hooks that run when a conversation starts and ends. The voice stack you build from plugins: speech-to-text (STT), an LLM, and text-to-speech (TTS), plus voice activity detection (VAD), turn detection, and noise cancellation. Starts a session on demand. It hosts your agent, connects to the runtime, and handles each conversation. ### A single turn A single turn in Zero Runtime: caller audio flows through noise cancellation, voice activity detection, speech-to-text, turn detection, the LLM, and text-to-speech, then back to the caller, who can interrupt at any time.

A single turn in Zero Runtime: caller audio flows through noise cancellation, voice activity detection, speech-to-text, turn detection, the LLM, and text-to-speech, then back to the caller, who can interrupt at any time.

Each time the caller speaks: 1. **Noise cancellation** cleans up the audio. 2. **Voice activity detection (VAD)** notices that someone is speaking. 3. **Speech-to-text (STT)** turns the speech into text. 4. **Turn detection** decides when the caller has finished, so the agent doesn't cut in too early. 5. **The LLM** writes the reply. 6. **Text-to-speech (TTS)** speaks it back. The caller can interrupt at any time. The runtime stops talking and listens again. ### Who runs what Who runs what in Zero Runtime: a caller connects to Zero Runtime, which we manage and which runs transport, GPUs, and the speech-to-text, LLM, and text-to-speech pipeline; it connects to your worker, which you run and which holds your agent's instructions, logic, and tools.

Who runs what in Zero Runtime: a caller connects to Zero Runtime, which we manage and which runs transport, GPUs, and the speech-to-text, LLM, and text-to-speech pipeline; it connects to your worker, which you run and which holds your agent's instructions, logic, and tools.

| | Your process | Runtime | | ---------------------------- | ------------ | ------- | | Agent instructions and logic | Yes | No | | Tool execution | Yes | No | | Transport, GPUs, turn-taking | No | Yes | | Autoscaling | No | Yes | Your agent logic and tools run on your side. The hard real-time infrastructure, the part that has to be fast and always available, is ours. ## When it fits Zero Runtime is built for phone agents, replacing phone menus (IVR), customer-support voice bots, voice assistants, and automated outbound or inbound calls. It fits when you want to own the agent code but not the real-time infrastructure.