Proof of Grass: an on‑device verifier that ensures you go outside

Description and use

Proof of Grass is a single‑file web app that recommends optimal outdoor windows and verifies outdoor photos using an on‑device vision model, keeping all data local and free of backend dependencies.

Problem

People spend too much time on screens and need a lightweight way to decide when to go outside and prove they did.

Outcome

The app runs entirely in the browser, requires no backend or API keys, and keeps user photos local, enabling a privacy‑friendly, zero‑cost "touch grass" habit tracker.

Workflow

• 1. User enters city or shares location.
• 2. App fetches weather data from Open‑Meteo and scores daylight hours using a heuristic.
• 3. App highlights the best "grass window" for the day.
• 4. User takes a photo outside and uploads it in the browser.
• 5. Transformers.js loads the CLIP ViT‑B/32 model (≈150 MB) and runs zero‑shot image classification.
• 6. The model compares probabilities for outdoor vs. indoor labels and verifies the photo is outdoors.
• 7. If verified, a Certificate of Grass is issued and the streak counter in localStorage is incremented.

Evidence

Proof of Grass is a one‑file web app that does two things: It tells you when to go outside…

Source

The first photo triggers a one‑time model download (~150 MB, then cached by the browser). After that it works offline.

Source

Open‑Meteo for the forecast and geocoding (free, no key, open‑source).

Source

Open-weight model: OpenAI's CLIP ViT‑B/32, in the ONNX conversion Xenova/clip‑vit‑base‑patch32 on the Hugging Face Hub.

Source