Showing the pattern, hiding the numberShowing the pattern, hiding the number

Dime is an open-source iPhone expense tracker, made by someone else. Logging a purchase takes seconds, and that is what a phone is good at. Reading patterns across months is harder on a small screen: which categories drift, when in the week I spend, whether a month was unusual.

In May 2026 I built a desktop-browser companion for my own use. It reads the CSV file that Dime exports and turns it into ten views of the same transactions. I call it Dime Insights here. No one else uses it.

Two days after the first version, I added one switch to the sidebar: Hide amounts. I wanted to show the charts, on a shared screen or in a portfolio like this one, without showing how much money I have.

This case is about that switch. It is also about the places it missed, which I found later.

The importer expects exactly one format: Dime's own CSV export, with five columns (date, note, amount, category and type). It is not a general bank-statement reader. The upload screen shows the expected format before you drop the file, so the contract is visible up front.

Transactions are saved in this browser's local storage, so a reload brings the dashboard back. There is no account and no sync. I haven't done a network audit, so I don't promise more than that: the data is kept in the browser.

Some details that matter for my use:

• Rupees, grouped the Nepali way. Amounts print as Rs with lakh grouping (Rs 1,00,000), the format I read without thinking.
• Desktop only. A fixed sidebar holds navigation and every global control. It is not designed for phones; the phone already has Dime.
• Plain methods. The forecast is a straight trend line over past months, labelled as linear regression.

"Hide amounts" can mean several things. I compared three:

I chose C. With the switch on, every formatted amount becomes a fixed placeholder, "———". Chart shapes, percentages, counts and dates stay. You can still see that May was 16% lower than April, which category is the largest, and which day of the week is expensive. You can't see what any of it adds up to.

Two small choices made C work:

• A fixed-width placeholder. Three dashes for every amount, so the mask doesn't reveal whether a number has two digits or six.
• One formatter behind the switch. Money shown in a stat or a tooltip goes through one shared formatter that checks the switch. Adding the mask did not mean touching every chart separately.

The sidebar said "Amounts hidden". But not every amount went through that formatter.

When I went back through the app for this write-up, I found that the first version of the mask missed several places:

• Chart axes. Seventeen Y-axis scales across seven sections built their own "Rs.20k"-style labels instead of using the shared formatter. With the mask on, a viewer could still read the scale off the side of the chart, and from the scale, roughly how big every bar is.
• Generated sentences. The insight cards put amounts straight into their sentences, before the mask can see them.
• Bucket labels and what-if figures. The spending distribution labels its ranges in rupees, and the what-if forecast prints its difference as a rupee string.

The mechanism was right. The coverage was not, because formatting money wasn't in one place yet. Some parts of the app formatted amounts on their own, and a switch can only hide what passes through it.

A second gap is quieter. The switch resets to off when the page reloads, so opening the app on a shared screen shows the numbers first.

The app has a Pricing page, three Pro-only sections and a few blurred Pro cards. None of it takes payments. There is no checkout, the plan buttons do nothing, and a "Test Pro" switch in the sidebar unlocks everything. I built it to try out how the features would be packaged, not to sell anything.

It taught me one thing worth keeping: a blurred card is not concealment, because the real chart is still drawn underneath. That doesn't matter for a test gate. It would matter for anything private, which is one more reason the amount mask replaces text instead of blurring it.

Status: a personal tool, used only by me. All data on this page is synthetic.

Measured outcome: none. There are no other users and nothing to measure beyond my own use. A screen-by-screen check with the switch on is the first test in the plan below.

Three lessons:

1. Privacy has to cover every surface. Values, tooltips, axes, generated sentences and labels all print money. A mask that covers most of them tells the viewer something false: that the screen is safe.
2. A privacy default should survive a reload. If the safe state resets, the unsafe state is what a shared screen shows first.
3. State the contract, and hold the file to it. The upload screen tells you which export it expects. The importer should be just as strict, and show what it couldn't read instead of guessing.