CityZen

Overview

Fig. 1 CityZen Logo

Crowdsourced sustainability ratings, shown right where people decide to buy.

CityZen is a browser extension that adds a community-driven sustainability score to Amazon product pages. Shoppers can see how others rate a product's sustainability and add their own vote, without leaving the page or doing any research.

CityZen was born out of Startup Summer 2021, the University of Sheffield's programme for turning ideas into ventures.

Status: early-stage prototype / proof of concept. See Current state and Roadmap for what works today and what's next.

The problem

Most people say they care about sustainability, but the information they need is missing when they make the purchase decision:

Ratings are hard to find. Sustainability data is scattered across brand sites, certifications and NGO reports, and almost nobody checks them mid-purchase.
Marketplaces optimise for price and speed. Reviews cover quality and delivery, not environmental or ethical impact.
"Greenwashing" erodes trust. Self-reported claims from sellers are hard to verify, so shoppers discount them.

If consumers were aware of an item's sustainability rating, they would take it into account when buying. The gap is awareness at the point of purchase.

The solution

CityZen puts a sustainability score into the Amazon product page, in the right-hand buy box column where shoppers already look.

Crowd-sourced: ratings come from people, not seller claims, in the same way reviews and Wikipedia work.
Zero friction: a single up/down vote, with no account, form or research required.
In context: the signal appears at the moment of purchase, which is when it can change behaviour.

Entrepreneurial angle

CityZen is a venture hypothesis as well as a codebase. This section sets out the thinking behind it.

Value proposition

For	CityZen offers
Conscious shoppers	A fast, trustworthy sustainability signal at the point of purchase
Sustainable brands	A way to be discovered and rewarded for doing the right thing
Retailers and platforms	Evidence of consumer demand for greener products
Researchers and policymakers	Aggregated data on what shoppers care about and where information gaps are

Target market

Beachhead: environmentally aware, UK-based Amazon shoppers (the extension currently targets amazon.co.uk), starting with students and young professionals who are digitally native and values-driven.
Expansion: other Amazon regions, other marketplaces, then any e-commerce site.

Why crowdsourcing

Low cost to start. There is no need to audit thousands of supply chains up front; the community does the work.
Network effects. More votes make scores more useful, which attracts more users, who add more votes.
Defensible data. Over time, a large dataset of consumer sustainability sentiment, linked to products by ASIN, becomes hard to replicate.

Possible business models

These are hypotheses to test, and none are implemented:

Freemium + insights: the extension stays free for consumers. Brands pay for analytics on how shoppers perceive their products.
Verified-brand programme: brands with third-party certifications can display a verified badge alongside the crowd score.
Affiliate revenue: earn commission on purchases made through the extension, disclosed transparently and with ratings kept independent of commission.
Data licensing: anonymised, aggregated sentiment data for researchers, NGOs and policy bodies.

Key risks and how we'd address them

Risk	Mitigation
Vote manipulation / brigading	Account or device-level rate limiting, weighted trust scores, anomaly detection
Platform dependency (relies on Amazon's page structure and policies)	Modular content scripts, expansion to multiple retailers, and a standalone web presence
Cold start (scores are empty until people vote)	Seed ratings from public certifications (e.g. B Corp, Fairtrade) and launch in focused communities first
Credibility of crowd ratings	Show vote counts, add optional evidence links, and separate "crowd" from "verified" signals

Validation plan

The riskiest assumptions are that shoppers want this and that they will vote. Early metrics to track:

Extension installs and weekly active users
Product pages viewed with a score visible
Vote rate (votes per page view)
Whether the score influences decisions (via lightweight in-extension surveys)

Current state

What the prototype does today:

Detects Amazon UK product pages (amazon.co.uk and smile.amazon.co.uk)
Injects a sustainability score box above the buy box
Shows upvote and downvote counts and a running score
Lets a user vote, or undo their vote, with the score updating immediately

Known limitations, which are the next things to fix:

Votes are loaded from a single hosted JSON document, so the same score appears on every product rather than being tracked per product.
Vote changes are applied locally and are not yet persisted to a backend.
There is no user identity or abuse protection yet.
It only supports Amazon UK, and only Chromium-style Manifest V2 extensions.

Helper functions for reading the product ASIN and category from the page already exist in src/js/content/product_util.js. They are the foundation for per-product scoring.

Roadmap

Per-product scores keyed by ASIN
Backend API and database to persist votes
Anti-abuse measures (rate limiting, trust weighting)
Category-level context (compare against similar products)
Evidence links and short written reasons with votes
Migrate to Manifest V3 and support Firefox
More marketplaces and regions
Brand-facing insights dashboard

Getting started

Prerequisites

Node.js and Yarn

Install and build

shell

yarn install
yarn build

The build output goes to the build/ folder.

Development

shell

yarn start

Load the extension in Chrome

Open chrome://extensions
Enable Developer mode
Click Load unpacked and select the build/ folder
Visit any product page on amazon.co.uk to see the CityZen box

Project structure

src/
├── manifest.json             # Extension manifest
├── js/
│   ├── content.js            # Content script entry point
│   ├── content/
│   │   ├── inject_counter.js # Builds and injects the score box, handles voting
│   │   └── product_util.js   # Product page detection, ASIN and category helpers
│   ├── background.js
│   ├── popup.js
│   └── options.js
├── counter_html.html         # Markup for the score box
└── css/                      # Popup and options styles
utils/                        # Build and dev-server scripts
webpack.config.js

Contributing

CityZen is early and open to ideas, whether you're a developer, designer, sustainability expert or someone interested in building the venture. Open an issue or a pull request to get involved.

License

Released under the MIT License.