phi-core

Simple, effective agent loop in Rust.

phi-core is a library for building LLM-powered agents that can use tools. It provides the core loop — prompt the model, execute tool calls, feed results back — and gets out of your way.

Philosophy

The loop is the product. An agent is just a loop: send messages to an LLM, get back text and tool calls, execute the tools, repeat until the model stops. phi-core implements this loop with streaming, cancellation, context management, and multi-provider support — so you don't have to.

Features

  • Streaming events — Real-time AgentEvent stream for UI updates (text deltas, thinking, tool execution)
  • Multi-provider — Anthropic, OpenAI, Google Gemini, Amazon Bedrock, Azure OpenAI, and any OpenAI-compatible API
  • Tool system — AgentTool trait with built-in coding tools (bash, file read/write/edit, search)
  • Context management — Automatic token estimation, tiered compaction (truncate tool outputs → summarize → drop old messages)
  • Execution limits — Max turns, tokens, and wall-clock time
  • Steering & follow-ups — Interrupt the agent mid-run or queue work for after it finishes
  • Cancellation — CancellationToken-based abort at any point
  • Builder pattern — Ergonomic BasicAgent struct with chainable configuration; Agent trait for polymorphism
  • Config-driven construction — TOML/JSON/YAML config → agent_from_config() → Arc<dyn Agent>
  • Session persistence — SessionRecorder materializes structured session/loop/turn records from events
  • Sub-agents — Delegate tasks to child agent loops via SubAgentTool
  • MCP integration — Connect to external tool servers via Model Context Protocol (stdio + HTTP)
  • Evaluational parallelism — Run N configs concurrently, select the best result via EvaluationStrategy

Ecosystem

phi-core is part of the LazyBouy ecosystem. It powers the agent backend for Phi applications.