onthefly-ai 0.1.3

Interactive ML Development in VS Code.

OnTheFly

OnTheFly is a VS Code extension + Python package for interactive PyTorch training. Run your training script exactly as you do today; while it trains, a VS Code dashboard can:

• stream per-sample loss, metrics, logs, and runtime stats
• pause/resume training and trigger tests
• export/import sessions (with optimizer state) for reproducible resumes
• fork short specialists on rough regions and merge improvements

Everything is local/offline with no accounts or external services. Sessions are ephemeral until you export them, so saving or exporting is how you keep a run around.

[!IMPORTANT] Project status: Beta. APIs, UI flows, and file formats may change before v1.0. Expect rough edges and please report issues. Currently, the console only supports PyTorch modules and Lightning trainers, in addition to our native trainer.

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Contents

• When should you use OnTheFly?
• Getting Started
• Interactive Training Loop
• License
• Citation

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OnTheFly turns model development into a tight, iterative loop:

As new data arrives, any previous session can be resumed with its full optimizer state, enabling controlled continuation rather than full retrains. Real-time visibility into pain points makes continuous improvement a measurable, iterative experimentation workflow rather than a one-off job.

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When should you use OnTheFly?

OnTheFly is aimed at people who:

• train PyTorch models (classification, regression, etc.) and want more actionability than TensorBoard/print logs
• are currently using no trainer or a lightning trainer
• prefer a local, offline workflow inside VS Code rather than cloud dashboards

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Getting Started

Quickstart (Python + VS Code)

1. Launch OnTheFly: Show Dashboard from the Command Palette (Cmd/Ctrl+Shift+P).
2. pip install onthefly-ai inside the same Python environment as your training script.
3. Run your script exactly as you do today; as soon as it calls Trainer.fit(...) or attach_lightning(...), the VS Code dashboard listens on localhost:47621 and attaches automatically.

The Python backend prints [onthefly] dashboard connected on tcp://127.0.0.1:47621 when the dashboard is available. You can open the dashboard before or after launching the script—the session backfills metrics and keeps streaming so you can pause, resume, and trigger tests at any time.

Install

1) VS Code extension

• Install “OnTheFly” from the VS Code Marketplace (or use the .vsix while it’s unpublished).

2) Python package

pip install onthefly-ai

Optional extras (quote the spec so your shell doesn’t expand the brackets):

• Data Explorer downloads (pandas>=2.0, scikit-learn>=1.3, umap-learn>=0.5): pip install "onthefly-ai[explorer]"
• GPU metrics (pynvml>=11.5): pip install "onthefly-ai[metrics]"

Requirements

• Visual Studio Code 1.102+
• Python ≥ 3.9
• PyTorch ≥ 2.2 (CUDA 12.x optional)
• OS: Linux, macOS, or Windows

Minimal PyTorch script

Show PyTorch example

import torch
from torch import nn
from torch.utils.data import DataLoader, TensorDataset

from onthefly import Trainer


def build_loaders():
    x = torch.randn(4096, 32)
    y = (x[:, :6].sum(dim=1) > 0).long()
    dataset = TensorDataset(x, y)
    train_ds, val_ds, test_ds = torch.utils.data.random_split(
        dataset, [3072, 768, 256], generator=torch.Generator().manual_seed(0)
    )
    return (
        DataLoader(train_ds, batch_size=128, shuffle=True),
        DataLoader(val_ds, batch_size=256),
        DataLoader(test_ds, batch_size=256),
    )


def main():
    train_loader, val_loader, test_loader = build_loaders()

    model = nn.Sequential(nn.Linear(32, 64), nn.ReLU(), nn.Linear(64, 2))
    optimizer = torch.optim.Adam(model.parameters(), lr=3e-4)
    loss_fn = nn.CrossEntropyLoss()

    trainer = Trainer(
        project="demo",
        run_name="baseline",
        max_epochs=3,
        do_test_after=True,
        val_every_n_epochs=1,
    )

    trainer.fit(
        model=model,
        optimizer=optimizer,
        loss_fn=loss_fn,
        train_loader=train_loader,
        val_loader=val_loader,
        test_loader=test_loader,
    )


if __name__ == "__main__":
    main()

Minimal Lightning script

Show Lightning example

import lightning as L
import torch
from torch import nn
from torch.utils.data import DataLoader, TensorDataset

from onthefly import attach_lightning


class LitClassifier(L.LightningModule):
    def __init__(self):
        super().__init__()
        self.net = nn.Sequential(nn.Linear(32, 64), nn.ReLU(), nn.Linear(64, 2))
        self.loss = nn.CrossEntropyLoss()

    def forward(self, x):
        return self.net(x)

    def training_step(self, batch, _):
        x, y = batch
        loss = self.loss(self(x), y)
        self.log("loss", loss, prog_bar=True)
        return loss

    def validation_step(self, batch, _):
        x, y = batch
        loss = self.loss(self(x), y)
        self.log("val_loss", loss, prog_bar=True)

    def configure_optimizers(self):
        return torch.optim.Adam(self.parameters(), lr=3e-4)


def make_loaders():
    x = torch.randn(4096, 32)
    y = (x[:, :6].sum(dim=1) > 0).long()
    ds = TensorDataset(x, y)
    train_ds, val_ds = torch.utils.data.random_split(
        ds, [3072, 1024], generator=torch.Generator().manual_seed(0)
    )
    return (
        DataLoader(train_ds, batch_size=128, shuffle=True),
        DataLoader(val_ds, batch_size=256),
    )


def main():
    train_loader, val_loader = make_loaders()

    model = LitClassifier()
    trainer = L.Trainer(max_epochs=3, log_every_n_steps=1)

    attach_lightning(
        trainer=trainer,
        model=model,
        project="demo",
        run_name="lightning-baseline",
        train_loader=train_loader,
        val_loader=val_loader,
        loss_fn=model.loss,
        do_test_after=True,
    )

    trainer.fit(model, train_loader, val_loader)


if __name__ == "__main__":
    main()

Open the dashboard tab whenever you want visibility, then run your script via python train.py (or whatever you already use). As soon as the trainer reaches Trainer.fit(...), the VS Code tab attaches (see Quickstart), begins streaming metrics, and accepts dashboard commands. Close the tab whenever you like; the script keeps running until you stop it with Ctrl+C.

attach_lightning(...) simply wraps the Lightning trainer so you can keep calling trainer.fit(...) exactly as before. Pass the dataloaders you want available in the dashboard plus a callable loss function; everything else is optional.

OnTheFly Trainer skips validation unless you pass val_every_n_epochs. Set it to the cadence you need (e.g., 1 for every epoch); omit or set 0 to disable validation entirely. When do_test_after=True, the automatic evaluation runs once the stop condition hits, and then the trainer keeps streaming so you can continue interacting with the run from VS Code.

Storage

To support rapid model development and keep the app lightweight, we don't currently store metadata in cloud. That means you are responsible for exporting sessions that you want to save. Starting a new session or resetting the current one will clean out the previous session’s storage.

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Interactive Training Loop (How To + Features)

Train → Observe → Pause → Focus → Compare → Merge → Export/Resume
Use all of OnTheFly, or just the parts you want (forking is optional).

1) Observe training in real time

• Stream per-sample loss (optionally grad-norm, margin) plus robust quantiles to surface tails early
• Track metrics, logs, and runtime stats from inside VS Code (no cloud, no accounts)

2) Intervene safely mid-run

• Pause/Resume anytime to take a clean snapshot and avoid “hope-and-pray” long runs
• Trigger mid-run tests and health checks (determinism, gradients, instability signals) before committing more budget

3) Focus on failure regions (optional)

• Mine hard samples (loss tails / residual clusters) and fork short-budget specialists
• Export slice indices/rows to CSV / Parquet / JSON for notebook debugging or dataset fixes

4) Compare specialists and choose what to keep

• Evaluate experts side-by-side on target slices
• Inspect lineage (parent/children) before you commit to a merge

5) Merge improvements into one model

• Merge via SWA, distillation, Fisher Soup, or adapter fusion
• Resume training from the merged model without restarting the whole run

6) Make runs reproducible and portable

• Export sessions (model + optimizer state) for controlled continuation instead of full retrains
• Import sessions later to run tests, generate reports, or extend training

Works with: PyTorch nn.Module + standard DataLoaders, and Lightning via attach_lightning(...)
Also: AMP support • deterministic actions (pause/fork/resume/load) • fully local/offline

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License

This project is licensed under the MIT License – see the LICENSE.txt file for details.

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Citation

If you use this project in research, please cite:

@software{onthefly2025,
  title        = {OnTheFly: Human-in-the-Loop ML Orchestrator},
  author       = {Luke Skertich},
  year         = {2025},
  url          = {https://github.com/KSkert/onthefly}
}