From a $209 Surprise Charge to a Chrome Extension: BillSensor's First 2.5 Months
Status: Live on Chrome Web Store Installs: 42 Revenue: $0 Reviews: 6 x 5-star
Why I Built This
On May 11, 2026, I started building BillSensor. The trigger was a charge I didn't expect.
I had cancelled a popular design tool, got the confirmation email, and moved on. Then a charge appeared on my card for $209. Turned out I was on an "annual plan billed monthly": a contract structure that looks like a monthly subscription but exits like an annual one. The early termination fee was 50% of whatever was left on the year. It was disclosed somewhere in the sign-up flow, in a tooltip I had scrolled past.
Spent an hour on chat support getting it reversed. The reversal worked, but the experience stayed with me.
I started reading Trustpilot reviews for the tools in my stack. Then for tools my clients used. The same complaints kept appearing independently across dozens of different products. "Charged after cancelling." "No cancel button." "Renewed with no warning." A 2023 Stanford and Texas A&M study confirmed what I was seeing: subscriber inattention increases company revenue by between 14% and 200%, depending on the service. This isn't a side effect of subscription models. It's a design choice.
I decided to build something about it.
What BillSensor Does
BillSensor is a Chrome extension that detects SaaS billing emails and alerts users before renewal charges.
For Gmail users, it reads billing emails passively as they're opened, with no Google account connection, no OAuth permission, and no setup required. Install and it works immediately.
For Outlook and Microsoft 365 users, a one-time connected scan via the extension popup surfaces 12 months of billing history instantly.
The feature I'm most proud of: a dark pattern scoring system. Every detected subscription gets a score from 1 to 10 based on how aggressively that tool uses billing tactics: hidden cancellation fees, post-cancellation charges, silent plan upgrades, seat additions without consent. Adobe scores 9/10. DocuSign scores 9/10. Zapier scores 8/10. These aren't opinions. They're based on Trustpilot complaint data, Reddit thread analysis, and regulatory filings including two federal settlements closed in 2026.
No competitor currently offers this. Every other subscription tracker treats all tools as equal billing risks.
The Build: 2.5 Months, Solo
I'm an IIT grad based in Kolkata, India. This is my first consumer-facing product. I've been building software for clients for years. This is the first time I built something because a problem made me angry enough to fix it.
Tech stack:
Chrome Extension Manifest V3, vanilla JavaScript
Node.js + Express backend
MySQL on Hostinger
Paddle as payment processor and Merchant of Record
Resend for transactional email
Key technical decisions:
The no-OAuth approach for Gmail was the most important architectural choice. Competitors like SaaS Subscription Tracker and CostLoop require Gmail OAuth, which triggers a "read and change your email" permission warning on install. That warning kills conversion. Passive DOM reading bypasses it entirely. The extension reads emails as users open them naturally, without any account connection.
The dark pattern scoring database required the most non-technical work. I spent several weeks going through Trustpilot reviews, Reddit threads, and regulatory filings to build credible scores for 62 tools. The Adobe and Shutterstock DOJ/FTC settlements were primary sources.
Payments through Paddle were a deliberate choice for an Indian-founded product selling internationally. Paddle acts as Merchant of Record, which handles global tax compliance automatically. No manual VAT, no GST complications.
Launch: What Happened in Week 1
Chrome Web Store: 42 installs, 6 five-star reviews. Majority of installs from the US.
Reddit: Posted a PSA on r/FuckAdobe about Adobe's cancellation fee and the DOJ settlement with no product mention in the post. 11,000 views in 24 hours, 1 comment. The username did the rest.
Blog: Published 4 posts targeting high-volume search queries. All indexed within 24 hours of publishing. Currently ranking at positions 4-15 across 64+ keywords. That surprised me. I expected organic search to take months.
Directories: Submitted to AlternativeTo, F6S, SaaSHub, G2, Capterra, GoodFirms, SoftwareSuggest, SpotSaaS, Future Tools, TechReviewer, and a few others. Most are pending approval or in queue.
Reviews: 6 five-star reviews. All from users I'd never interacted with. That felt better than the install count.
What Didn't Work
Reddit sitewide filter. The account got flagged after a few rapid posting attempts across subreddits. Every subsequent post, regardless of content, format, or links, gets auto-removed by Reddit's filter. Still working through this. r/StartUpIndia went through and got genuine engagement. r/SideProject has removed every attempt.
r/chrome_extensions. Posted there, it went live, got 130 views over 8 hours. The subreddit is 41K members but almost no engagement.
Where I Am Now
Pre-revenue. Zero paying users. 42 installs.
The next milestone is 100 installs before spending anything on paid acquisition or the CASA assessment required for Gmail bulk scan, which is the Pro feature that justifies the $9/month price point. The passive detection alone is genuinely useful. The goal is proving enough users agree before investing further.
What I think is working: The blog content strategy is producing results faster than expected. Ranking for "Adobe charged after cancelling subscription" and similar queries at position 4-15 in week 1 is ahead of what I planned. The dark pattern angle resonates. It gives the content a point of view that pure subscription tracking posts don't have.
What I'm unsure about: Free-to-paid conversion once I have more users. The free plan is deliberately generous: unlimited passive detection, no artificial caps on what you can detect. The bet is that seeing a dark pattern score of 9/10 next to an Adobe subscription, combined with a renewal alert 7 days before the charge, is enough of an "aha moment" to convert. I haven't been able to test this yet.
What's Next
100 installs
First paying user
Post-cancellation monitoring (Phase 2, no competitor has this)
Outlook multi-account support
Product Hunt launch (planning once reviews and install velocity are stronger)
Happy to answer questions about the build, the no-OAuth detection approach, the dark pattern scoring methodology, or anything else.
BillSensor. Chrome Web Store: Add to Chrome
Exactly — forecasting and subscription visibility are two sides of the same coin. I love your roadmap toward email platforms and eventual API/web app. Surfacing subscription data inside finance tools like Finsight AI would be a natural fit.
Really useful — SMBs I talk to often get blindsided by surprise SaaS charges too. With Finsight AI, I’m focused on forecasting cashflow, and visibility into recurring charges is a big part of that. Curious how you plan to expand beyond Chrome extensions?
That's exactly the overlap — cashflow forecasting and subscription visibility are two sides of the same problem. You can't forecast accurately if recurring charges are showing up as surprises.
On expansion beyond Chrome: the roadmap goes email platform first (Outlook is already live, Gmail bulk scan is next), then post-cancellation monitoring which no competitor currently does. After that, the logical step is a web app or API that could plug into tools like yours — surfacing subscription data where finance decisions are already being made rather than requiring users to open a separate extension. Nothing built yet on that front but it's the direction that makes sense.
The interesting part is that the free tier isn't just a preview — it already delivers a meaningful version of the core protection.
So the unanswered question may be less “will people find BillSensor useful?” and more whether the reason to keep using it becomes a reason to pay for it.
Those are two different things to validate.
That's the sharpest version of the conversion problem I've seen stated. "Useful" and "worth paying for" are genuinely different validations and I haven't separated them clearly enough yet.
The working hypothesis is that the free plan creates the habit (checking scores, seeing renewal dates) and the paid features solve the acute pain when it hits (being charged after cancellation, needing a PDF record for a dispute). But that's a hypothesis. I won't know if it holds until someone actually hits that moment and decides whether $9 is worth it. That's the experiment the next few weeks will run.
That’s helpful context. The distinction between something being useful and something being valuable enough to pay for is an important one.
I’d like to continue the conversation outside the thread. What’s the best email to reach you on?