Imported from reason-machines/codex-skills (skills/nanocodex-rust-agent-framework/SKILL.md). Install upstream with npx skills add reason-machines/codex-skills --skill nanocodex-rust-agent-framework. Copyright stays with the author.

Nanocodex Rust Agent Framework

Skill by ara.so — Codex Skills collection.

Nanocodex is a Rust framework for building frontier OpenAI agents with modular, composable components. It provides building blocks for agent lifecycle management, OpenAI API integration, tool execution, and observability. The framework emphasizes small, excellent components with sharp boundaries: an OpenAI client works without an agent loop, tools work without a CLI, and the agent orchestrates these pieces cleanly.

Installation

CLI Installation

Install the Nanocodex CLI on macOS or Linux:

curl -fsSL https://nanocodex.paradigm.xyz | bash

Switch between versions:

nanocodex update                 # latest stable
nanocodex update 0.2.0           # specific version
nanocodex update --nightly       # nightly build
nanocodex update --pr 50         # PR artifact (requires gh CLI)
nanocodex update --path ./nanocodex  # local binary

Rust Library

Add to your Cargo.toml:

[dependencies]
nanocodex = "0.2"

# Or with observability support
nanocodex = { version = "0.2", features = ["observability"] }

# Or use individual components
nanocodex-agent = "0.2"
nanocodex-oai-api = "0.2"
nanocodex-tools = "0.2"

Core Components

Nanocodex is organized into distinct layers:

• nanocodex - Facade with common imports and prelude
• nanocodex-agent - Agent lifecycle, prompt ordering, tool loop, cancellation
• nanocodex-oai-api - OpenAI WebSocket client, authentication, session management
• nanocodex-tools - Tool runtime, workspace tools, MCP support
• nanocodex-observability - OpenTelemetry tracing and metrics

Basic Agent Setup

Minimal Agent Example

use nanocodex::{Nanocodex, OpenAi};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let openai = OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;
    
    let (agent, mut events) = Nanocodex::builder(openai)
        .instructions(
            "You are a Rust coding agent. Make focused changes, \
             preserve unrelated work, and run relevant tests before finishing."
        )
        .workspace(std::env::current_dir()?)
        .build()?;

    // Spawn event listener
    let event_task = tokio::spawn(async move {
        while let Some(event) = events.recv().await {
            eprintln!("event {}: {:?}", event.seq, event.kind);
            if event.kind.is_terminal() {
                break;
            }
        }
    });

    // Send prompt and await result
    let result = agent
        .prompt("Find and fix the failing parser test.")
        .await?
        .await?;

    event_task.await?;
    println!("{}", result.final_message());
    
    Ok(())
}

Streaming Agent Response

Stream deltas as they arrive:

use nanocodex::{Nanocodex, OpenAi};
use nanocodex::agent::events::{AgentEventData, AssistantEvent};
use futures_util::StreamExt;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let openai = OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;
    let (agent, _events) = Nanocodex::builder(openai)
        .instructions("You are a helpful assistant.")
        .build()?;

    let mut turn = agent.prompt("Explain async/await in Rust").await?;
    
    while let Some(event) = turn.next().await {
        if let AgentEventData::Assistant(AssistantEvent::Delta(delta)) = event.data()? {
            print!("{}", delta.text);
        }
    }
    
    let result = turn.await?;
    println!("\n\nFinal: {}", result.final_message());
    
    Ok(())
}

Agent Builder Configuration

Workspace and Instructions

use nanocodex::{Nanocodex, OpenAi};
use std::path::PathBuf;

let openai = OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;

let (agent, events) = Nanocodex::builder(openai)
    .instructions("You are a Rust expert focused on performance and correctness.")
    .workspace(PathBuf::from("/path/to/project"))
    .build()?;

Custom Tools

Register custom tools with the agent:

use nanocodex::{Nanocodex, OpenAi};
use nanocodex::tools::{Tool, Tools};
use serde::{Deserialize, Serialize};
use async_trait::async_trait;

#[derive(Debug, Deserialize)]
struct FetchUrlParams {
    url: String,
}

#[derive(Debug, Serialize)]
struct FetchUrlResult {
    content: String,
    status: u16,
}

struct FetchUrlTool;

#[async_trait]
impl Tool for FetchUrlTool {
    fn name(&self) -> &str {
        "fetch_url"
    }

    fn description(&self) -> &str {
        "Fetch content from a URL"
    }

    fn parameters_schema(&self) -> serde_json::Value {
        serde_json::json!({
            "type": "object",
            "properties": {
                "url": {
                    "type": "string",
                    "description": "The URL to fetch"
                }
            },
            "required": ["url"]
        })
    }

    async fn execute(
        &self,
        params: serde_json::Value,
    ) -> Result<serde_json::Value, Box<dyn std::error::Error + Send + Sync>> {
        let params: FetchUrlParams = serde_json::from_value(params)?;
        let response = reqwest::get(&params.url).await?;
        let status = response.status().as_u16();
        let content = response.text().await?;
        
        let result = FetchUrlResult { content, status };
        Ok(serde_json::to_value(result)?)
    }
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let openai = OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;
    
    let mut tools = Tools::new();
    tools.register(FetchUrlTool);
    
    let (agent, _events) = Nanocodex::builder(openai)
        .instructions("You can fetch URLs to help users.")
        .tools(tools)
        .build()?;
    
    let result = agent
        .prompt("Fetch https://example.com and summarize it")
        .await?
        .await?;
    
    println!("{}", result.final_message());
    Ok(())
}

Using the Tool Macro

Simplify tool creation with the #[tool] macro:

use nanocodex::tools::tool;
use serde::{Deserialize, Serialize};

#[derive(Deserialize)]
struct CalculateParams {
    expression: String,
}

#[derive(Serialize)]
struct CalculateResult {
    result: f64,
}

#[tool(
    name = "calculate",
    description = "Evaluate a mathematical expression"
)]
async fn calculate(params: CalculateParams) -> Result<CalculateResult, String> {
    // Simple example - real implementation would parse expression
    Ok(CalculateResult { result: 42.0 })
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let openai = nanocodex::OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;
    
    let mut tools = nanocodex::tools::Tools::new();
    tools.register(calculate);
    
    let (agent, _events) = nanocodex::Nanocodex::builder(openai)
        .tools(tools)
        .build()?;
    
    Ok(())
}

OpenAI API Client (Standalone)

Use the OpenAI client without the full agent:

use nanocodex::oai::{OpenAi, Message, MessageContent, Role};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;
    
    let session = client.session().await?;
    
    let messages = vec![
        Message {
            role: Role::User,
            content: MessageContent::Text("Hello, how are you?".to_string()),
        }
    ];
    
    let mut turn = session.chat(messages).await?;
    
    while let Some(response) = turn.next().await {
        let response = response?;
        if let Some(text) = response.text() {
            print!("{}", text);
        }
    }
    
    Ok(())
}

Session Management

Multi-Turn Conversations

The agent automatically maintains conversation history:

use nanocodex::{Nanocodex, OpenAi};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let openai = OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;
    let (agent, _events) = Nanocodex::builder(openai)
        .instructions("You are a helpful assistant.")
        .build()?;

    // First turn
    let result1 = agent
        .prompt("My name is Alice")
        .await?
        .await?;
    println!("Turn 1: {}", result1.final_message());

    // Second turn - agent remembers context
    let result2 = agent
        .prompt("What's my name?")
        .await?
        .await?;
    println!("Turn 2: {}", result2.final_message());
    
    Ok(())
}

Cloning Agent Handles

Create cheap clones for concurrent access:

let agent_clone = agent.clone();

tokio::spawn(async move {
    let result = agent_clone
        .prompt("Background task")
        .await?
        .await?;
    Ok::<_, Box<dyn std::error::Error>>(())
});

Forking Sessions

Create branching conversations:

// Fork from current state
let forked_agent = agent.fork().await?;

// Fork from specific snapshot
let snapshot_id = result.snapshot_id();
let branched_agent = agent.fork_from(snapshot_id).await?;

// Spawn new independent session
let spawned_agent = agent.spawn().await?;

CLI Usage

Interactive TUI Mode

nanocodex

One-Shot Commands

nanocodex run "implement a binary search function in src/search.rs"

VM-Backed Tools

Run tools in an isolated VM:

# Build VM guest runtime
just build-vm-guest

# Run with VM backing
nanocodex \
  --vm .nanocodex/vm/session-rootfs.ext4 \
  --vm-guest-runtime target/aarch64-unknown-linux-musl/debug/nanocodex-vm-guest \
  --vm-workspace /app

# One-shot with VM
nanocodex run "inspect the repository" \
  --vm .nanocodex/vm/session-rootfs.ext4 \
  --vm-guest-runtime target/aarch64-unknown-linux-musl/debug/nanocodex-vm-guest \
  --vm-workspace /app

Observability

Enable Tracing

use nanocodex::observability::{init_tracing, TracingConfig};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    init_tracing(TracingConfig::default())?;
    
    let openai = nanocodex::OpenAi::new(std::env::var("OPENAI_API_KEY")?)?;
    let (agent, _events) = nanocodex::Nanocodex::builder(openai).build()?;
    
    // Agent operations will now emit structured traces
    let result = agent.prompt("test").await?.await?;
    
    Ok(())
}

OpenTelemetry Integration

use nanocodex::observability::{init_tracing, TracingConfig};
use opentelemetry::global;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = TracingConfig {
        endpoint: Some("http://localhost:4317".to_string()),
        service_name: "my-agent".to_string(),
        ..Default::default()
    };
    
    init_tracing(config)?;
    
    // Your agent code here
    
    global::shutdown_tracer_provider();
    Ok(())
}

Common Patterns

Error Handling

use nanocodex::{Nanocodex, OpenAi};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let openai = match OpenAi::new(std::env::var("OPENAI_API_KEY")?) {
        Ok(client) => client,
        Err(e) => {
            eprintln!("Failed to create OpenAI client: {}", e);
            return Err(e.into());
        }
    };
    
    let (agent, _events) = Nanocodex::builder(openai).build()?;
    
    match agent.prompt("test").await {
        Ok(turn) => {
            match turn.await {
                Ok(result) => println!("{}", result.final_message()),
                Err(e) => eprintln!("Turn failed: {}", e),
            }
        }
        Err(e) => eprintln!("Failed to send prompt: {}", e),
    }
    
    Ok(())
}

Timeout Handling

use tokio::time::{timeout, Duration};

let result = timeout(
    Duration::from_secs(60),
    agent.prompt("complex task").await?.await,
).await??;

Cost Tracking

let result = agent.prompt("analyze this code").await?.await?;

if let Some(usage) = result.usage() {
    println!("Tokens used: {} input, {} output", 
             usage.input_tokens, 
             usage.output_tokens);
    if let Some(cost) = usage.estimated_cost_usd() {
        println!("Estimated cost: ${:.4}", cost);
    }
}

Troubleshooting

Authentication Issues

Ensure OPENAI_API_KEY is set:

export OPENAI_API_KEY=sk-...

For ChatGPT authentication instead of API keys, use:

let openai = OpenAi::from_chatgpt_auth()?;

WebSocket Connection Failures

The client automatically handles reconnection and replay. If persistent issues occur:

1. Check network connectivity
2. Verify API key permissions
3. Ensure no firewall blocking WebSocket connections
4. Review rate limits on your OpenAI account

Tool Execution Errors

Debug tool calls with event monitoring:

let event_task = tokio::spawn(async move {
    while let Some(event) = events.recv().await {
        match &event.kind {
            nanocodex::agent::EventKind::ToolCall { name, args } => {
                eprintln!("Tool called: {} with {:?}", name, args);
            }
            nanocodex::agent::EventKind::ToolResult { result } => {
                eprintln!("Tool result: {:?}", result);
            }
            _ => {}
        }
    }
});

Memory and Context Management

The agent handles compaction automatically. To monitor context size:

if let Some(usage) = result.usage() {
    if usage.input_tokens > 100_000 {
        eprintln!("Warning: Large context ({} tokens)", usage.input_tokens);
    }
}

VM Issues

When using VM-backed tools:

1. Ensure VM guest runtime is built for correct architecture
2. Check VM image has nanocodex-vm-guest in /usr/local/bin
3. Verify workspace path exists in VM
4. On macOS, ensure proper code signing for VM binaries

Configuration Files

AGENTS.md Discovery

Place AGENTS.md in your workspace root for agent context:

# Project Context

This is a Rust library for parsing configuration files.

## Key Files
- `src/parser.rs` - Main parsing logic
- `src/config.rs` - Configuration structures

## Testing
Run tests with: `cargo test`

The agent automatically discovers and uses this context.

Best Practices

1. Use typed results: Leverage TurnResult for structured access to messages, usage, and snapshots
2. Monitor events: Subscribe to the event stream for debugging and telemetry
3. Clone efficiently: Use agent.clone() for concurrent access to the same session
4. Handle errors gracefully: The double-await pattern allows separate error handling for prompt submission and completion
5. Provide clear instructions: Set detailed system instructions via the builder
6. Organize tools: Group related tools and use clear naming conventions
7. Track costs: Monitor token usage and estimated costs in production