What causes an upgrade cost curve that gets cheaper at higher levels?

The cost formula mixed an additive and a multiplicative term whose interaction produced a non-monotonic curve, so some later levels cost less than earlier ones.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix an Upgrade Cost Curve That Gets Cheaper at Higher Levels

Quick answer: Use a monotonic cost function of level, evaluate it across the full level range to confirm it never decreases, and clamp or redesign any segment that dips.

An upgrade that briefly gets cheaper as you level it lets players skip ahead and buy out of order. Ensuring the cost curve rises monotonically across every level fixes it. Here is how.

How to fix it

1. Pick a monotonic formula

Use a function whose output strictly increases with level, such as base * growth ** level or a strictly increasing polynomial, rather than a mix that can dip.

2. Sweep the whole range

Evaluate the cost at every level from 1 to max and assert each is greater than the previous; a dip anywhere means the formula is wrong, not just a rounding artifact.

3. Watch integer rounding

Rounding a smooth curve to whole currency can create flat or backward steps near small differences; round consistently and verify monotonicity after rounding.

4. Add a guard test

Keep a test that fails if any consecutive pair of levels has a non-increasing cost, so future formula tweaks cannot reintroduce the dip.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every HTML5 error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

The errors you never hear about are the ones quietly costing you players. Visibility turns them into a worklist.