Psych Runtime

A Python library for running AI agents inside your application. It runs an agent's tool calls, saves a Run's progress as it goes, pauses for approval before the calls you choose, and records everything a Run did so you can read it back. You supply the model, the tools and the database.

psychruntime.com · Documentation · Browser demo · Changelog

Status: pre-alpha. The public API changes between minor releases, and every breaking change is in CHANGELOG.md before it ships. Names scheduled for removal warn for at least one minor release first. The PyPI badge above shows the current release.

What it looks like

One agent, one tool, offline. The test suite runs this file on every commit.

import asyncio
import psych_runtime
from psych_runtime.testing.fake_model import FakeModel


async def lookup_order(order_id: str) -> dict[str, str]:
    """Look up an order by its id."""
    return {"order_id": order_id, "status": "shipped"}


spec = psych_runtime.AgentSpec(
    name="support",
    instructions="Help the customer with their order.",
    model=psych_runtime.ModelRef(model="fake-standard"),
    tools=(psych_runtime.CodeTool(name="lookup_order"),),
)


async def main() -> None:
    model = (
        FakeModel()
        .turn(text="Checking.", tool_calls=[("lookup_order", {"order_id": "A1"})])
        .turn(text="A1 has shipped.")
    )
    async with psych_runtime.session(model, tools=[lookup_order]) as s:
        view = await s.ask(spec, "where is order A1?")
        print(view.text)  # A1 has shipped.

        report = await psych_runtime.report(s.store, view.run_id)
        print(report.totals.usage, report.totals.cost)


asyncio.run(main())

A1 has shipped.
input=0 output=0 cache_read=0 cache_write=0 cache_write_1h=0 reasoning=0 None

The tool ran: report.tool_calls says so, from the log. Cost is None because no price table was passed; it is never rounded to zero.

Run it

Python 3.12 or newer. The package depends on pydantic and httpx.

pip install psych-runtime
psych new demo && cd demo && python main.py

Expected:

No OPENAI_API_KEY set, so this run uses the fake model.

Order A1 has shipped with DHL.

completed | 1 turn, 1 tool call | 0 tokens | cost None

Set OPENAI_API_KEY and the same file calls a real provider. psych new writes a main.py you own; the command line never runs an agent for you.

• The distribution is psych-runtime, the import is psych_runtime, the command is psych.
• session() defaults to an in-memory store that dies with the process. Pass a PostgresStore, MySQLStore or DynamoDBStore for anything that must survive a restart.
• Get started walks through the file above, then a real model, a second tool, and reading a Run back.

What it handles

Where it runs

Psych is a dependency you import, not a service you deploy. Your request handler admits a Run and returns; a Worker in a process of yours claims it and executes it; the two share your database and nothing else.

Psych brings no HTTP server, auth, user model, scheduler, UI, prompt library, eval framework, vector store, budget enforcement or model router. Your application already has those, and a library that brought its own would argue with them. psych new api --template fastapi shows the split.

Limitations worth knowing before you build on it:

• Only what you register is safe to retry. After a crash, a tool call recorded as started is settled unknown unless it was registered safe_to_retry=True. Psych does not make an external side effect repeatable; it refuses to guess.
• A sandbox says what it proved, not what it hopes. Every backend grades ten guarantees per execution and reports the isolation level it actually reached; output produced under weaker terms than were requested is withheld rather than returned. A plain subprocess limits a program and does not isolate it, and it says so. Namespaces and containers reach a kernel boundary; no local backend reaches one on macOS or Windows, where a request for full isolation is refused instead of approximated.
• Cost is only as good as its source. Cost.source distinguishes an amount returned by the provider from one estimated using the bundled, dated price snapshot or your override. A model with no known price records cost=None. Token totals carry their own usage_source; missing provider usage is never presented as a measured zero.
• Provider support is the OpenAI-compatible chat API. One client reaches OpenAI and any gateway that speaks the same protocol; anything else is a ModelClient you implement.

The example console

git clone https://github.com/psych-systems/psych-runtime && cd psych-runtime
docker compose up --build        # then http://localhost:3000

examples/playground/ is an application built on the library: publish an agent, talk to it, watch the log, read the report. It supplies the HTTP server and the UI Psych does not. It is an example, not a hardened service; do not put it on the public internet.

For coding agents

The repository ships 26 skills, one per feature, in .agents/skills/. Give your coding agent this instruction:

Read https://raw.githubusercontent.com/psych-systems/psych-runtime/main/.agents/skills/psych/SKILL.md
and follow it to add Psych to this project.

psych skills install copies them into a project.

Documentation

psychruntime.com/docs is generated from this repository: the API reference from psych_runtime.__all__, the guides from the skills above, the changelog and design notes copied verbatim. The build fails when any page disagrees with its source.

• DESIGN.md, the settled design.
• docs/design-notes/, why each area is shaped the way it is.
• docs/api.md, the public API with a worked example the test suite runs.
• docs/deployment.md, what a deployment is responsible for: scope, secrets, sandboxes, retention.

Contributing, support and security

• CONTRIBUTING.md: what is welcome, how to set up, and what a change has to pass.
• Issues for bugs and questions. Most bugs reproduce against the fake model with no provider and no network; a failing test beats a description.
• SECURITY.md: report vulnerabilities privately through the advisory form, never as a public issue.

Development

uv sync --all-extras --group dev
scripts/dev-services.sh start        # real Postgres, MySQL and DynamoDB Local
scripts/check.sh                     # ruff, mypy --strict, import-linter, generated docs, three test layers

Licence

Apache-2.0. See LICENSE, and NOTICE for the one third-party attribution the package carries.