PydanTask: Deep Agentic Harness for Pydantic AI

PydanTask is an alpha harness for building deep, multi-step agents on top of Pydantic AI.

If you want agents that can plan, execute, self-critique, and ship a final artifact (not just chat), this gives you the backbone.

What you get:

• Dynamic task DAGs: a supervisor creates/patches a task graph at runtime
• Parallel execution: run dependency-satisfied tasks concurrently
• Critic QA + retries: failed tasks become RERUN until max_attempts, then FAILED
• Observability: optional tracing (Langfuse, Logfire, LangSmith)
• Recovery/auditability: optional event-sourced checkpointing (events.jsonl + summaries + large-result sidecars)
• Extensibility: register your own capabilities via CapabilityDescription

Try it in ~3 minutes

1. Install:

pip install pydantask

2. Set env vars:

export OPENAI_API_KEY="..."
# Optional: enables Tavily web search; otherwise DuckDuckGo-based search is used
export TAVILY_API_KEY="..."

3. Run a minimal agent:

import asyncio
from pydantask.agents import DeepAgent


async def main() -> None:
    agent = DeepAgent(
        objective="Compare 3 open-source LLMs for local inference and recommend one.",
        model="openai:gpt-4.1-mini",  # or "anthropic:..." or pass a Model instance
        trace=False,
        checkpoint=False,
        max_steps=10,
    )

    result = await agent.run()
    print(result.final_result.detailed_output if result.final_result else result.errors)


if __name__ == "__main__":
    asyncio.run(main())

Alpha note: the core loop is working and tested, but the API and prompts are still evolving. If you hit rough edges, please open an issue with a minimal repro.

For deeper docs and API reference, see: pydantask.readthedocs.io

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High-Level Architecture

The core orchestrator is DeepAgent:

from pydantask.agents.agent import DeepAgent

DeepAgent coordinates several built‑in agents:

• Supervisor – plans and chooses which tasks to run next, based on statuses and dependencies.
• Researcher – performs web/external research for tasks that need new information.
• Producer – synthesizes intermediate results into a final answer or artifact.
• Critic – evaluates task outputs and drives deterministic retry/fail transitions.

They all operate over a shared RuntimeState:

from pydantask.models import RuntimeState, TaskItem, TaskResult, Plan

Key concepts:

• Plan (Plan):
  • reasoning_steps: planner’s internal notes
  • tasks: list of TaskItem instances
• TaskItem: one sub‑task in the plan, with:
  • task_id, overall_objective, sub_task_objective
  • capability (which sub‑agent to use, e.g. "research_agent")
  • sub_task_dependencies (other task IDs that must complete first)
  • status (TaskStatus: PENDING, READY, RUNNING, NEEDS_REVIEW, COMPLETED, FAILED, ERRORED, RERUN)
  • result (TaskResult) and task_feedback (TaskQAResult)
• RuntimeState:
  • plan: Dict[int, TaskItem]
  • objective: str
  • capability_registry: Dict[str, CapabilityDescription] (excluded from serialization)
  • document_store, knowledge_store, runtime_steps, etc.

The control loop in DeepAgent.run():

1. Supervisor incrementally builds a task DAG for the objective (via tools like add_task).
2. RuntimeState is initialized with the capability registry.
3. In each cycle:
   • Supervisor decides which tasks to execute next based on plan progress, task dependencies, and self reflection.
   • Ready tasks, so long as dependencies are satisfied, are executed by the appropriate capability (sub‑agent).
   • Critic reviews each result and produces a "QA" report for the supervisor to review if the task failed.
4. Loop stops when:
   • the Supervisor sets all_tasks_completed = True and the run’s completion invariants are met (exactly one task is marked is_final=True, and that task is COMPLETED with a TaskResult), or
   • max_steps is reached, or
   • the harness stops after several no-progress cycles (safety guardrail).

For more detail, see docs/agents.md.

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Installation & Setup

PydanTask assumes you already have Pydantic AI and an OpenAI‑compatible model configured. A Tavily API key is optional for the built‑in research agent (it falls back to DuckDuckGo search if omitted).

1. Install dependencies

From your project root:

pip install pydantask

(or however you manage your environment; if you use Poetry, adjust accordingly.)

2. Environment variables

Set the following environment variables (e.g. in your shell or a .env file):

• OPENAI_API_KEY – for the underlying OpenAIChatModel (or whatever your Pydantic AI provider expects).
• TAVILY_API_KEY – (optional) used by the research_agent (via tavily_search_tool). If this key is not set, it defaults to DuckDuckGo search.

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Quickstart: Running a DeepAgent

Minimal example that creates a DeepAgent and runs it on a single objective:

import asyncio

from pydantask.agents.agent import DeepAgent

async def main() -> None:
    agent = DeepAgent(
        objective="Write an overview of ghost lights folklore and summarize scientific explanations.",
        model="gpt-4.1-mini",  # or any compatible OpenAIChatModel name
        max_steps=10,
    )

    run_result = await agent.run()
    runtime_state = run_result.runtime_state

    # Inspect the final plan and results
    for task_id, task in sorted(runtime_state.plan.items()):
        print(f"Task {task_id} [{task.status}]: {task.sub_task_objective}")
        if task.result is not None:
            print("  Summary:", task.result.summary)
            # The main long-form output for the task is stored in-memory:
            print("  Detailed output:", (task.result.detailed_output or "<empty>"))
            print()

if __name__ == "__main__":
    asyncio.run(main())

What this does:

1. Constructs a DeepAgent with default Supervisor, Researcher, Producer, and Critic.
2. Supervisor (dynamic DAG architect) breaks down the objective into TaskItems using built-in capabilities.
3. Supervisor picks tasks to run in each loop iteration.
4. Researcher and Producer execute those tasks and return structured TaskResults.
5. Critic evaluates each task result and marks tasks as:
   • COMPLETED when QA passes
   • RERUN when QA fails but retries remain (critic feedback is appended to the task objective)
   • FAILED when QA fails and max_attempts is exceeded
6. When done, you get a RuntimeState with the full plan and results.

Note: by default, this harness treats task artifacts as in-memory outputs (e.g. TaskResult.detailed_output).

However, it does support optional event-sourced checkpointing (checkpoint=True) which persists an append-only events.jsonl log (plus summaries and, when needed, sidecar JSON files for large results) under _checkpoint/.

Filesystem tools exist in pydantask.tools.default_tools, but they are not enabled by default in the built-in agents.

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Customizing Capabilities

You can add custom sub‑agents or tools via CapabilityDescription and the sub_agents argument.

Example: custom agent capability

from pydantic_ai import Agent
from pydantask.agents.agent import DeepAgent
from pydantask.models import CapabilityDescription, TaskResult, TaskRunDeps

my_special_agent = Agent(
    model=...,  # e.g. the same OpenAIChatModel
    name="_my_special_agent",
    system_prompt="You are a specialized agent for security analysis.",
    deps_type=TaskRunDeps,   # gives tools access to deps.runtime_state + deps.task
    output_type=TaskResult,
    tools=[...],  # tools should typically accept RunContext[TaskRunDeps]
)

custom_capability = CapabilityDescription(
    name="security_agent",  # used in TaskItem.capability
    description="Performs security-focused analysis and risk assessment.",
    tool_func=my_special_agent,
)

agent = DeepAgent(
    objective="Assess the security posture of this web application.",
    sub_agents=[custom_capability],
)

# Now the Planner can choose `security_agent` as a capability in the plan.

Example: simple function capability (runnable capability)

DeepAgent expects a capability to be runnable (i.e. something with a .run(prompt, deps, usage_limits=...) method). For plain functions, wrap them with as_runner(...).

from pydantask.agents.agent import DeepAgent
from pydantask.capabilities.runner import as_runner
from pydantask.models import CapabilityDescription, TaskResult, TaskRunDeps


async def my_utility_capability(prompt: str, deps: TaskRunDeps) -> TaskResult:
    # prompt is the task prompt; deps.runtime_state + deps.task give you context
    return TaskResult(task_id=deps.task.task_id, summary="processed", detailed_output=prompt)


utility_capability = CapabilityDescription(
    name="my_utility_tool",
    description="Utility capability that processes a prompt and returns a TaskResult.",
    tool_func=as_runner(my_utility_capability),
)

agent = DeepAgent(objective="Some goal...", sub_agents=[utility_capability])

For more customization details, see:

• docs/customization.md
• docs/tools.md
• docs/agents.md

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Running Unit Tests

Tests live under the test/ directory and are written to be compatible with both pytest and the standard library unittest.

Recommended: pytest

From the repository root:

pip install pytest
pytest

Using unittest directly

If you prefer unittest, you can still run the suite with:

python -m unittest discover -s test -p "test_*.py"

Make sure required environment variables (e.g. TAVILY_API_KEY, OPENAI_API_KEY) are set, or that tests patch them appropriately (as in test/test_agent.py).

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