PROMPTLINE

Calibrate → Optimize → Gate → Serve. Promptline is an open-source, pip-installable pipeline for automatic prompt optimization: it calibrates an LLM-as-judge against human labels (with a measurable agreement certificate), evolves your system prompt with from-scratch implementations of state-of-the-art optimizers (GEPA flagship), refuses to deploy anything that isn't a statistically significant improvement over the incumbent, and serves the active prompt from a versioned registry over HTTP. Existing tools are either optimizers that trust their metric blindly (DSPy, gepa, promptim, AdalFlow) or eval platforms that inspect judges but don't optimize (promptfoo, Braintrust, Weave) — no other open-source tool chains calibrated judge → optimizer → statistical deploy gate. Promptline is that chain.

Before / after

The demo starts from a deliberately mediocre seed and lets GEPA earn its keep:

- You are a support agent. Answer the question.
+ You are a senior customer-support agent. For every customer message:
+ 1. Acknowledge the specific problem in one empathetic sentence — never a
+    generic apology.
+ 2. Give the concrete resolution or exact next steps (menu paths, timelines,
+    fees), pulling details from the conversation rather than restating policy.
+ 3. If information is missing (order number, email), ask for exactly what you
+    need and say what you'll do once you have it.
+ 4. Close by offering the relevant follow-up action (refund, replacement,
+    escalation) — do not deflect to "contact support"; you are support.
+ Keep answers under 120 words. Do not pad, upsell, or ask for reviews.

…and the gate only promotes it if the paired bootstrap CI on a held-out split excludes zero.

Installation

Install the published package

For using Promptline as a tool or library. The PyPI distribution is promptline-opt; it imports as promptline (like scikit-learn → sklearn).

pip install "promptline-opt[data]"    # [data] pulls HF `datasets` for the loaders
#   or: uv add "promptline-opt[data]"
#   or without loaders: pip install promptline-opt

export OPENROUTER_API_KEY=sk-or-...   # bring your own key → all major models
promptline --version

The wheel ships the Python package, CLI, TUI, and FastAPI server. The React dashboard is not bundled — see Dashboard below if you want the web UI.

From source (local development)

For hacking on Promptline itself, or running the dashboard from a clone:

git clone https://github.com/sanskarpan/promptline.git
cd promptline

uv sync --all-extras --dev          # runtime + [data] + dev tools (pinned via uv.lock)
uv run promptline --version

make check                          # lint + format-check + pyright + pytest (the CI gate)

Common local targets (make help lists all): make test, make web-build, make e2e, make live-smoke.

Quickstart

promptline demo setup                 # datasets + config (see examples/support-assistant/)
cd examples/support-assistant/workspace

promptline calibrate --gold gold.jsonl --label-min 0 --label-max 4
promptline optimize --optimizer gepa --data train.jsonl
promptline gate --candidate <best_id> --dev dev.jsonl --val val.jsonl
promptline serve                      # GET /prompts/support/active

Prefix with uv run when working from a clone (uv run promptline demo setup, …).

No key? promptline demo setup --offline plus the PROMPTLINE_FAKE_SCRIPT fake client rehearses the whole pipeline deterministically — see examples/support-assistant/README.md.

Dashboard (optional)

The dashboard is only available from a source checkout (the published wheel does not include web/dist). Build it, then serve hosts it automatically:

cd web && npm install && npm run build   # then, from the workspace: promptline serve

Without the build, serve prints a warning and the API (control + serving planes) works as usual.

Architecture

Library-core with thin shells: CLI, TUI, and FastAPI server are thin layers over one Python package; the web dashboard is a static React app served by FastAPI.

┌─────────────────────────────────────────────┐
│  Interfaces (thin, replaceable)             │
│  ┌─────────┐ ┌─────────┐ ┌───────────────┐  │
│  │   CLI   │ │   TUI   │ │ Web dashboard │  │
│  │ (Typer) │ │(Textual)│ │ (React/Vite)  │  │
│  └────┬────┘ └────┬────┘ └───────┬───────┘  │
│       │           │        FastAPI + SSE    │
│  ─────┴───────────┴──────────────┴────────  │
│              Python core library            │
│  ┌──────────┐ ┌───────┐ ┌────────────────┐  │
│  │Optimizers│ │ Judge │ │ Eval harness   │  │
│  │GEPA/MIPRO│ │+calib.│ │ + stat gate    │  │
│  └──────────┘ └───────┘ └────────────────┘  │
│  ┌──────────┐ ┌───────────────────────────┐ │
│  │OpenRouter│ │ Registry (SQLite+files)   │ │
│  │ adapter  │ │ versions, lineage, active │ │
│  └──────────┘ └───────────────────────────┘ │
└─────────────────────────────────────────────┘

The pipeline

 gold labels          train.jsonl              dev + val splits
      │                    │                          │
      ▼                    ▼                          ▼
 ┌───────────┐      ┌────────────┐      ┌──────────────────────┐
 │ calibrate │─────▶│  optimize  │─────▶│         gate         │
 │ judge vs  │ cert │ GEPA/MIPRO │ best │ paired bootstrap CI  │
 │ humans, κ │      │ /ProTeGi/… │ cand │ + Holm + val confirm │
 └───────────┘      └────────────┘      └──────────┬───────────┘
                                          promote  │  reject
                                                   ▼
                                        ┌──────────────────────┐
                                        │  registry (SQLite)   │──▶ serve
                                        │  versions + lineage  │    GET /prompts/
                                        │  + active pointer    │    {program}/active
                                        └──────────────────────┘    (ETag)

Every stage refuses bad inputs: optimize and gate refuse to score with an uncalibrated judge (missing or failed certificate → exit 2; --allow-uncalibrated overrides with a loud warning), undersized eval sets, contaminated dev/val splits.

The judge is the metric

By default optimize and gate score candidates with the calibrated LLM judge configured under judge: in promptline.yaml (scores normalized to [0, 1], references read from labels['reference']):

judge:
  enabled: true           # false → fall back to exact-match on labels['answer']
  criterion: helpfulness  # rubric criterion; also the certificate filename stem
  # description: ""       # custom rubric text (default: built-in per criterion)
  # scale_min: 1
  # scale_max: 5
  # certificate: ""       # default: <registry>/certificates/<criterion>.json
  min_kappa: 0.6          # certificate must attest at least this kappa

judge.certificate is the primary certificate location (gate.certificate is still honored for back-compat). promptline calibrate writes the certificate exactly where optimize/gate look for it, so calibration genuinely unlocks the rest of the chain.

Optimizers

All implemented from scratch against one contract (optimize(program, seed, trainset, metric, budget, harness, emit)), all budget-metered, all emitting typed run events.

Optimizer	One-liner	Paper
GEPA (flagship)	Per-instance Pareto frontier + reflective mutation from execution traces, system-aware merges, strict minibatch acceptance	arXiv 2507.19457
MIPRO	Bootstrapped demo sets × grounded instruction proposals, searched jointly with TPE (Optuna) and periodic full evals	arXiv 2406.11695
BootstrapFewShot (+RS)	Teacher traces that pass the metric become few-shot demos; random search over demo subsets	DSPy (Khattab et al. 2023)
ProTeGi	Textual gradients: critique failures → counter-edit → paraphrase, with CAPO-style successive-halving racing	EMNLP 2023, racing: arXiv 2504.16005
OPRO	Trajectory extrapolation: show (instruction, score) history sorted worst→best, ask for a better one. Needs a strong proposer model	arXiv 2309.03409

Concept docs: core · judge · optimizers · gate · serving

CLI reference

Command	What it does
promptline init	Scaffold a commented promptline.yaml
promptline demo setup [--offline]	Build the support-assistant demo workspace
promptline calibrate --gold <path|helpsteer2>	Certify the judge against human labels (κ threshold, saves certificate)
promptline optimize --optimizer gepa [--budget N] [--data f.jsonl] [--resume id]	Run an optimization pass; best candidate auto-registered
promptline gate --candidate <id> --dev d.jsonl --val v.jsonl	Statistically gate challengers vs the active prompt; promotes on win
promptline registry list|show|activate|rollback	Inspect versions/lineage, bootstrap a baseline, undo a promotion
promptline tui --run <id> | --attach <sse-url>	Live terminal cockpit for a run
promptline serve [--host] [--port]	Control plane + serving plane + dashboard over HTTP
promptline data prepare --demo	Alias forwarding to demo setup

Exit codes follow the pipeline's semantics: gate returns 0 promote / 1 reject / 2 refusal.

Dashboard & TUI

promptline tui is a Textual cockpit — score curve, per-example Pareto grid, candidate lineage, live event log with per-call cost, budget burn-down — attachable to live runs (SSE) or finished ones (events.jsonl). promptline serve also hosts the React dashboard (Runs, Lineage explorer, Judge calibration, Gate report, Registry).

Both share one design language: terminal-native in the style of opencode/Hermes — dark theme, monospace throughout, flat sharp-cornered panels with 1px borders, a single muted accent plus semantic green/red for verdicts, dense data-first layouts. No gradients, no glassmorphism.

Testing

uv run pytest -q          # fully offline: FakeLLMClient scripts, exact stats tests
uv run ruff check .

The suite runs without network or keys: deterministic scripted LLM responses, statistical functions validated on known distributions, API via FastAPI TestClient. An opt-in live smoke test (needs OPENROUTER_API_KEY) runs a 5-example/10-rollout pass against a cheap model. All real LLM calls are cached in SQLite, so crashed runs resume cheaply and recorded traces replay cassette-style.

License & citations

MIT.

• GEPA — Agrawal et al., arXiv 2507.19457
• MIPROv2 — Opsahl-Ong et al., arXiv 2406.11695
• ProTeGi / APO — Pryzant et al., EMNLP 2023, arXiv 2305.03495
• OPRO — Yang et al., arXiv 2309.03409
• CAPO (racing) — arXiv 2504.16005
• HelpSteer2 — Wang et al., arXiv 2406.08673 (CC-BY-4.0)
• LLM-judge biases — Zheng et al., arXiv 2306.05685
• EvalGen (criteria drift) — Shankar et al., arXiv 2404.12272