| name | ai-agent |
| description | Build an AI agent backend with persistent memory: one Rivet Actor per conversation, queued message handling, and streaming LLM responses as realtime events. |
AI Agent
IMPORTANT: Before doing anything, you MUST read BASE_SKILL.md in this skill's directory. It contains essential guidance on debugging, error handling, state management, deployment, and project setup. Those rules and patterns apply to all RivetKit work. Everything below assumes you have already read and understood it.
Working Examples
If you need a reference implementation, read the raw working example code in these templates:
Patterns for building AI agent backends with RivetKit, where each conversation is one Rivet Actor that owns its memory, its message queue, and its streaming output.
Starter Code
Start with one of the working examples on GitHub and adapt it. The sections below describe the flagship ai-agent example unless a variant is called out explicitly.
| Variant | Starter Code | Use When |
|---|
| Queue-driven AI SDK agent | GitHub | You want a streaming chat agent where each conversation keeps its own persistent memory and processes one message at a time. |
| Sandbox coding agent | GitHub | The agent should run a coding agent (Codex by default) inside an isolated sandbox via Docker, Daytona, or E2B. |
| Durable streams agent (experimental) | GitHub | You want replayable, restart-safe prompt and response delivery through durable streams instead of actor state and events. |
Conversation Memory
Use one actor per conversation, keyed by a conversation or agent id (see Actor Keys). The agent actor's persistent state is the conversation memory: in the ai-agent example, messages and status live in JSON actor state and survive sleep and restarts with no external database. Every model call rebuilds the prompt from c.state.messages plus a system prompt, so memory and inference input are the same data.
| Variant | Where Memory Lives | Persisted State Fields |
|---|
ai-agent | JSON actor state | messages, status |
sandbox-coding-agent | JSON actor state plus the sandbox ACP session | messages, status, sessionId |
experimental-durable-streams-ai-agent | Durable streams; the actor stores only its conversation id and a read cursor | conversationId, promptStreamOffset |
Message Handling
In the ai-agent example, the client pushes user input onto the agent's message queue with agent.connection.send("message", { text, sender }). This is a queue push, not an action call. The actor's run hook (see Lifecycle) consumes the queue serially with for await (const queued of c.queue.iter()).
Serial queue consumption is the per-conversation concurrency guarantee: at most one in-flight model call per actor, with no extra locking. The status field (thinking while a model call is in flight) is UI signal only; the run loop is the actual lock. The loop also checks c.aborted inside the token stream so shutdown exits gracefully.
| Variant | Message Ingress | Serialization Guarantee |
|---|
ai-agent | message queue pushed via connection.send | run hook pops one queued message at a time with c.queue.iter(). |
sandbox-coding-agent | sendMessage action, no queue | Each call awaits the sandbox round trip before broadcasting the result. |
experimental-durable-streams-ai-agent | Durable prompt stream long-polled from onWake | promptStreamOffset is persisted per chunk, so restarts resume without reprocessing prompts. |
Streaming Responses
The ai-agent actor broadcasts a response event for every model text delta. The payload carries messageId, the per-token delta, the cumulative content, and a done flag (plus error on failure), so clients can either append deltas or idempotently replace the message by messageId using content. The example frontend replaces by messageId, which tolerates dropped events. The terminal broadcast has an empty delta, the full content, and done: true.
Because the assistant message object lives in c.state.messages and is mutated in place during streaming, partial content persists if the actor restarts mid-stream. The example broadcasts once per AI SDK delta with no throttling; batching or throttling deltas is a recommended extension for high-traffic deployments, not something the example implements.
Variant differences: sandbox-coding-agent sends a single response broadcast with done: true after the sandbox finishes (no incremental streaming), and experimental-durable-streams-ai-agent appends per-token chunks to a durable response stream, then broadcasts responseComplete or responseError.
Architecture
| Topic | Summary |
|---|
| Topology | agentManager["primary"] singleton directory plus one agent[agentId] actor per conversation. |
| Ingress | Client pushes AgentQueueMessage payloads onto the agent's message queue with connection.send. |
| Streaming | One response broadcast per model delta, terminal broadcast with done: true. |
| Memory | Full transcript and status in JSON actor state; no external database. |
The manager creates AgentInfo records and warms each agent through actor-to-actor communication: createAgent calls c.client<typeof registry>(), then client.agent.getOrCreate([info.id]) and awaits getStatus() so the conversation actor exists before the client connects. The sandbox variant extends this topology with a codingSandbox actor that shares the agent's key (codingSandbox.getOrCreate([c.key[0]])), so the agent-to-sandbox mapping is implicit in the key space.
Actors
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Key: agentManager["primary"]
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Responsibility: Directory actor. Creates AgentInfo records, lists agents, and warms each agent actor via c.client().
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Actions
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Queues
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State
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Key: agent[agentId]
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Responsibility: One actor per conversation. Holds the full message history and status, consumes queued user messages in its run loop, calls the model via the AI SDK, and broadcasts streaming deltas.
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Actions
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Queues
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Events
messageAddedstatusresponse
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State
Lifecycle
sequenceDiagram
participant C as Client
participant AM as agentManager
participant A as agent
participant LLM as Model API
C->>AM: createAgent(name)
AM->>A: getOrCreate([info.id]) + getStatus()
AM-->>C: AgentInfo
C->>A: connection.send("message", {text, sender})
Note over A: run loop pops queue via c.queue.iter()
A-->>C: messageAdded (user message)
A-->>C: messageAdded (assistant placeholder)
A-->>C: status (thinking)
A->>LLM: streamText(system prompt + history)
loop each text delta
LLM-->>A: delta
A-->>C: response {messageId, delta, content, done: false}
end
A-->>C: response {delta: "", content, done: true}
A-->>C: status (idle)
Security Checklist
The examples ship without auth so they stay minimal. Apply this baseline before exposing an agent backend.
- API keys stay server-side:
OPENAI_API_KEY (or ANTHROPIC_API_KEY) is read by the AI SDK inside the actor process. The key never reaches the browser; clients only talk to the actor over RivetKit. The sandbox variant forwards keys into the sandbox env, never to the client.
- Add authentication: The examples have no auth, so anyone who reaches the server can create agents, list them, and message any agent whose key they can guess. Add
onBeforeConnect or createConnState checks with scoped tokens as a recommended extension. See Authentication.
- Validate and rate-limit queue payloads: The example only skips bodies without a string
text. Enforce payload size limits, schema validation, and per-connection rate limits as a recommended extension.
- Derive sender identity server-side: The example trusts the client-supplied
sender field verbatim. Bind sender identity to the authenticated connection instead.
- Cap or trim message history: The example sends the full transcript on every model call with no cap. Trim or summarize old messages as a recommended extension so prompts and state stay bounded.
- Set cost ceilings per conversation: Add per-agent token budgets and quotas as a recommended extension. The sandbox variant runs real compute, so also enforce per-user sandbox quotas and restrict sandbox network egress.
Reference Map
Actors
Cli
Clients
Cookbook
Deploy
General
Self Hosting
