fastaiagent 0.6.0

Build, debug, evaluate, and operate AI agents. The only SDK with fork-and-rerun Agent Replay.

FastAIAgent SDK

Build, debug, evaluate, and operate AI agents. The only SDK with Agent Replay — fork-and-rerun debugging for AI agents.

Works standalone or connected to the FastAIAgent Platform for visual editing, production monitoring, and team collaboration.

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Quickstart

from fastaiagent import Agent, LLMClient

# Create an LLM client
llm = LLMClient(provider="openai", model="gpt-4o")

# Create an agent
agent = Agent(
    name="my-agent",
    system_prompt="You are a helpful assistant.",
    llm=llm,
)

# Run it
result = agent.run("What is the capital of France?")
print(result.output)
print(result.trace_id)  # every run is traced — use this ID for replay/debugging

Debug a failing agent in 30 seconds

from fastaiagent.trace import Replay

# Load a trace from a production failure
replay = Replay.load("trace_abc123")

# Step through to find the problem
replay.step_through()
# Step 3: LLM hallucinated the refund policy ← found it

# Fork at the failing step, fix, rerun
forked = replay.fork_at(step=3)
forked.modify_prompt("Always cite the exact policy section...")
result = forked.rerun()

No other SDK can do this.

Evaluate agents systematically

from fastaiagent.eval import evaluate

results = evaluate(
    agent_fn=my_agent.run,
    dataset="test_cases.jsonl",
    scorers=["correctness", "relevance"]
)
print(results.summary())
# correctness: 92% | relevance: 88%

Trace any agent — yours or LangChain/CrewAI

import fastaiagent
fastaiagent.integrations.langchain.enable()

# Your existing LangChain agent, now with full tracing
result = langchain_agent.invoke({"input": "..."})
# → Traces stored locally or pushed to FastAIAgent Platform

Build agents with guardrails and cyclic workflows

from fastaiagent import Agent, Chain, LLMClient, Guardrail
from fastaiagent.guardrail import no_pii, json_valid

agent = Agent(
    name="support-bot",
    system_prompt="You are a helpful support agent...",
    llm=LLMClient(provider="openai", model="gpt-4o"),
    tools=[search_tool, refund_tool],
    guardrails=[no_pii(), json_valid()]
)

# Chains with loops (retry until quality is good enough)
chain = Chain("support-pipeline", state_schema=SupportState)
chain.add_node("research", agent=researcher)
chain.add_node("evaluate", agent=evaluator)
chain.add_node("respond", agent=responder)
chain.connect("research", "evaluate")
chain.connect("evaluate", "research", max_iterations=3, exit_condition="quality >= 0.8")
chain.connect("evaluate", "respond", condition="quality >= 0.8")

result = chain.execute({"message": "My order is late"}, trace=True)

Expose agents as MCP servers (Claude Desktop / Cursor / Continue / Zed)

Any Agent or Chain becomes an MCP server with one line:

from fastaiagent import Agent, LLMClient

agent = Agent(name="research_assistant", llm=LLMClient(provider="openai", model="gpt-4o"))

if __name__ == "__main__":
    import asyncio
    asyncio.run(agent.as_mcp_server(transport="stdio").run())

Register it in claude_desktop_config.json:

{
  "mcpServers": {
    "research-assistant": {
      "command": "python",
      "args": ["/absolute/path/to/my_agent.py"]
    }
  }
}

Claude Desktop now treats your fastaiagent as a callable tool. Same config shape for Cursor / Continue / Zed. Or use the CLI: fastaiagent mcp serve my_agent.py:agent. See docs/tools/mcp-server.md.

Install: pip install 'fastaiagent[mcp-server]'.

Peer-to-peer swarms with handoffs

Beyond the central-coordinator Supervisor/Worker pattern, agents can hand off to each other directly:

from fastaiagent import Agent, LLMClient, Swarm

llm = LLMClient(provider="openai", model="gpt-4o-mini")

triage = Agent(name="triage", llm=llm, system_prompt="Hand off to the right specialist.")
coder = Agent(name="coder", llm=llm, system_prompt="Answer Python questions.")
writer = Agent(name="writer", llm=llm, system_prompt="Help with prose.")

swarm = Swarm(
    name="help_desk",
    agents=[triage, coder, writer],
    entrypoint="triage",
    handoffs={"triage": ["coder", "writer"], "coder": [], "writer": []},
)
result = swarm.run("How do I reverse a list in Python?")

The currently active agent decides when to transfer control — no central LLM. See docs/agents/swarm.md for the full guide, and Swarm vs Supervisor for when to pick which.

Long-term memory with composable blocks

Beyond a sliding window, layer static facts, a rolling summary, semantic recall, and fact extraction into one memory object:

from fastaiagent import Agent, LLMClient, ComposableMemory, AgentMemory
from fastaiagent import StaticBlock, SummaryBlock, VectorBlock, FactExtractionBlock
from fastaiagent.kb.backends.faiss import FaissVectorStore

llm = LLMClient(provider="openai", model="gpt-4o-mini")

agent = Agent(
    name="assistant",
    llm=llm,
    memory=ComposableMemory(
        blocks=[
            StaticBlock("User is Upendra. Prefers terse answers."),
            SummaryBlock(llm=llm, keep_last=10, summarize_every=5),
            VectorBlock(store=FaissVectorStore(dimension=384)),
            FactExtractionBlock(llm=llm, max_facts=100),
        ],
        primary=AgentMemory(max_messages=20),
    ),
)

VectorBlock works with any VectorStore (Qdrant / Chroma / custom). Write your own block by subclassing MemoryBlock with two methods. See docs/agents/memory.md.

Swap the KB storage layer

Default LocalKB ships with FAISS + BM25 + SQLite — zero setup. Point at Qdrant, Chroma, or your own backend with one kwarg:

from fastaiagent.kb import LocalKB
from fastaiagent.kb.backends.qdrant import QdrantVectorStore

kb = LocalKB(
    name="product-docs",
    search_type="vector",
    vector_store=QdrantVectorStore(
        url="http://localhost:6333",
        collection="product-docs",
        dimension=1536,
    ),
)
kb.add("docs/")
results = kb.search("refund policy", top_k=5)

Adapters shipped: FAISS, BM25, SQLite (defaults), Qdrant (fastaiagent[qdrant]), Chroma (fastaiagent[chroma]). Write your own against the VectorStore / KeywordStore / MetadataStore protocols — see docs/knowledge-base/backends.md.

Shape agent behavior with middleware

Compose pre/post model hooks and tool wrappers without subclassing Agent:

from fastaiagent import Agent, LLMClient, TrimLongMessages, RedactPII, ToolBudget

agent = Agent(
    name="controlled",
    llm=LLMClient(provider="openai", model="gpt-4o"),
    tools=[search_tool],
    middleware=[
        TrimLongMessages(keep_last=30),   # cap history size
        RedactPII(),                      # scrub emails/phones/SSNs both directions
        ToolBudget(max_calls=5),          # cooperatively stop after 5 tool calls
    ],
)

Write your own by subclassing AgentMiddleware and overriding before_model, after_model, or wrap_tool. See docs/agents/middleware.md for ordering, hook reference, and custom patterns.

Multi-agent teams with context

from fastaiagent import Agent, LLMClient, RunContext, Supervisor, Worker, tool

@tool(name="get_tickets")
def get_tickets(ctx: RunContext[AppState], status: str) -> str:
    """Get support tickets for the current user."""
    return ctx.state.db.query("tickets", user_id=ctx.state.user_id, status=status)

support = Agent(name="support", llm=llm, tools=[get_tickets], system_prompt="Handle tickets.")
billing = Agent(name="billing", llm=llm, tools=[get_billing], system_prompt="Handle billing.")

supervisor = Supervisor(
    name="customer-service",
    llm=LLMClient(provider="openai", model="gpt-4o"),
    workers=[
        Worker(agent=support, role="support", description="Manages tickets"),
        Worker(agent=billing, role="billing", description="Handles billing"),
    ],
    system_prompt=lambda ctx: f"You lead support for {ctx.state.company}. Be helpful.",
)

# Context flows to all workers and their tools
ctx = RunContext(state=AppState(db=db, user_id="u-1", company="Acme"))
result = supervisor.run("Show my open tickets and billing", context=ctx)

# Stream the supervisor's response
async for event in supervisor.astream("Help me", context=ctx):
    if isinstance(event, TextDelta):
        print(event.text, end="")

Connect to FastAIAgent Platform (optional)

import fastaiagent as fa

fa.connect(api_key="fa-...", project="my-project")

# Traces automatically sent to platform dashboard
result = agent.run("Help me")

# Pull versioned prompts from platform
prompt = PromptRegistry().get("support-prompt")

# Publish eval results to platform
results = evaluate(agent, dataset=dataset)
results.publish()

SDK works standalone. Platform adds: production observability, prompt management, evaluation dashboards, team collaboration, HITL approval workflows.

Free tier available →

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Install

pip install fastaiagent

With optional integrations:

pip install "fastaiagent[openai]"       # OpenAI auto-tracing
pip install "fastaiagent[langchain]"    # LangChain auto-tracing
pip install "fastaiagent[kb]"           # Local knowledge base
pip install "fastaiagent[all]"          # Everything

Documentation

• Getting Started
• Agent Replay Guide
• Building Chains with Cycles
• Guardrails
• Evaluation
• API Reference

Contributing

We welcome contributions! See CONTRIBUTING.md for guidelines.

License

Apache 2.0 — see LICENSE.