This release is a pre-release and may not be stable for production use.
synth-containers
The task contract for Synth optimizers and evals — wrap any task as a small HTTP service that optimizers can target without touching your code.
PyPI · Optimizers · Cookbooks
A Synth container is a small HTTP service around a task. It owns the dataset, the
scoring/verifier logic, the mutable prompt or policy fields, and the policy-model
credential boundary. An optimizer like
synth-optimizers GEPA sees one URL
and a typed rollout contract — it never imports your task package or reads private
evaluator state. The same contract works whether the task is a classifier, a coding
agent, or a live game environment, and in Python, Rust, or TypeScript.
Install
pip install synth-containers
# or
uv add synth-containers
Local Synth development
Register the current checkout once after changing Containers or its package version:
./scripts/register-local-dev-build.sh
The command builds a wheel, installs it into an immutable machine-local directory, verifies the installed version, and atomically selects it for local Workshop builds. No launch flags or environment variables are required. Re-running it reuses an identical registered wheel.
Sibling Optimizers development remains editable through its checked-in uv source:
cd ../optimizers
uv sync --group dev
The contract
| Route | Method | Purpose |
|---|---|---|
/metadata |
GET | contract version + capabilities |
/program |
GET | mutable prompt fields + seed candidate |
/dataset |
GET | split names + row counts |
/dataset/rows |
POST | rows for a requested seed list |
/rollout |
POST | run a candidate on a row → reward + usage |
/health |
GET | liveness |
The Python SDK also provides Container, Container.serve(),
ContainerHandle, and ContainerConnection for URL-only optimizer handoff.
Use generic route hints and capability metadata here; optimizer-specific GEPA
settings belong in synth-optimizers.
Example
from fastapi import Body, FastAPI
from synth_containers import GEPA_OPTIMIZER_CONTRACT_VERSION
app = FastAPI()
@app.post("/rollout")
def rollout(payload: dict = Body(...)) -> dict:
candidate, row = payload["candidate"], payload["row"]
# run the task with the candidate's mutable fields, score it with a real verifier
return {"reward": ..., "usage": ...}
See the cookbooks for complete containers: Banking77, HotpotQA, MiniGrid, TBLite, and Crafter.
Links
- Optimizers — GEPA on this contract
- Cookbooks — runnable containers
- Agent skill — drop into a coding agent to build and debug containers
- Contract OpenAPI
License
MIT
1 maintainer
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