The engine

Prove the plan before it touches your account.

Stax replays your trading plan over years of real market prices, fees included, and shows you every buy and sell it would have made, with the reason for each one.

Test a plan free See how it works

staxlabs.org/labs · backtest result

Simulated account

$13,850

started with $10,000 · five years · fees included

vs. just buying the S&P 500

shown side by side

The verdict, in plain words: this plan grew a $10,000 practice account to $13,850 over five real years, and you can open every one of its 214 trades to see why it bought or sold.

5 years: of real prices
1,258: trading days simulated
214: trades, each with its reason
Next-day prices: no hindsight allowed

A guess is not a plan.

Most investing apps let you buy on a feeling. Stax makes the feeling take a test first.

History is the test.

Your plan trades through real years, real prices, and real bad weeks, before you commit anything.

Tuning is just more tests.

When Stax tunes your plan, it is running thousands of these tests and keeping what holds up.

What happens when you press Test

The whole run usually takes a few seconds. Here is what Stax does with your plan in that time.

It rebuilds the past, day by day
Stax walks your plan through each trading day in order. On every day, the plan only knows what an investor could have known that day. Tomorrow stays hidden, so the test cannot cheat.
It buys and sells at the next morning’s price
When your plan decides to buy a stock, the purchase happens at the next day’s opening price, the way a real order would. Trading fees come out of the simulated account on every single trade.
It writes down every move and why
Every buy and every sell is recorded with its reason: which rule fired, at what price, and what it did to your account. You can open any trade and read the story.
Eight independent checkers audit the run
Before you see a result, eight separate verification checks go over the simulation: the rules it followed, the prices it used, the fees it charged, the risk limits it obeyed. If something looks off, you see that too.

staxlabs.org/labs · backtest result

Simulated account

$13,850

started with $10,000 · five years · fees included

vs. just buying the S&P 500

shown side by side

The verdict, in plain words: this plan grew a $10,000 practice account to $13,850 over five real years, and you can open every one of its 214 trades to see why it bought or sold.

5 years: of real prices
1,258: trading days simulated
214: trades, each with its reason
Next-day prices: no hindsight allowed

One engine, not two

Tuning your plan is the same engine running thousands of tests.

Some apps sell you a "backtester" and an "optimizer" as if they were different machines. They are not. When Stax tunes your plan, it builds many versions of it, runs each one through the same honest history test, and shows you the versions that held up best.

You see each candidate’s full record: how it grew, how far it fell in its worst stretch, and how often it traded. You pick the version you trust, and it gets a real, complete test before it ever runs in a practice slot.

See the whole flow

The test is strict on purpose

5+ years
of market history available to test against: 8
independent checks audit every single run: 100%
of trades listed with their reason, fees included

A backtest shows how a plan behaved in the past. It is evidence, not a promise: markets change, and no test can tell you what next year holds.

Questions people ask

Does a good backtest mean the plan will make money?

No. It means the plan held up across real years, including bad ones, which is far more than a hunch can say. Markets change, so Stax also lets you run the plan in a practice slot with simulated cash and watch it handle the present before you trust it further.

Can the test peek at the future?

No, and this matters more than anything else. On each simulated day the plan only sees information that existed that day, and its trades fill at the next morning’s price. A test that peeks always looks brilliant and always falls apart in real life.

What do I see when a test finishes?

A chart of how your simulated account grew, shown next to what just buying the S&P 500 would have done. Its worst stretch, in dollars. And the full list of trades, each one openable to see which rule fired and what it cost.

Do I need to know how to code?

No. You can describe what you want in a chat and Buddi builds the plan, or you can start from a template. If you do write code, the same engine is open through the API and MCP.

What does it cost to run a test?

Testing a plan is part of the free tier, and your first full run of the whole flow costs nothing. Deeper stress tests, like replaying a plan through thousands of shuffled histories, use FinBucks, the in-app credit.