Building your first screener, step by step

A well-built screener replaces hours of chart scrolling with a few seconds of scanning: you define your criteria once, and it only shows you the assets that meet them. But a screener is only useful if its rules faithfully translate a strategy idea. This guide walks through the full method, from initial idea to automated scan, with a concrete example you can reproduce as is.

Step 1: start from a strategy idea

Never start by stacking indicators: start with a sentence. A good strategy idea fits on one line and describes a specific market situation. Our example for this guide: "buy pullbacks within an established uptrend". The intuition is classic : an asset in a long-term uptrend going through a temporary pullback often offers a better entry point than an asset at its highs.

Step 2: translate the idea into objective rules

Each part of the sentence becomes a measurable rule. "Established uptrend" translates to: close above the 200 SMA on the daily : the 200-period moving average is the most widely used long-term trend filter. "Pullback" translates to: RSI 14 below 40 on the daily : momentum has cooled off without necessarily reaching the extreme oversold zone. Two rules are enough to capture the idea:

• Rule 1 (trend): the closing price is above the 200 SMA, on the daily timeframe.
• Rule 2 (pullback): the RSI 14 is below 40, on the daily timeframe.

In Screener.Trading, each rule is built without code: you pick an indicator, an operator (above, below, between two bounds) and a comparison target : price, another indicator or a static value. You can also use candle offsets ("the condition was true 2 candles ago") and validity windows ("the cross happened at most 3 candles ago"), which are very handy for catching recent signals without requiring them to land exactly on the last candle.

Step 3: choose your asset universe

The same screener produces very different results depending on the universe it runs on. You can scan an entire market (all crypto pairs, for instance), an index like the S&P 500 or CAC 40, an asset category (ETFs, forex, commodities), or a personal watchlist. To start, an index universe is a good choice: S&P 500 names are liquid and well known, which limits nasty execution surprises. Watchlists become valuable later, when you want to focus your scans on the assets you actually follow.

Step 4: test the screener with a first scan

Run a first scan to check the calibration: within seconds you get the list of assets meeting all your rules at the last close, with each asset's chart one click away. At this stage the goal is simply to confirm that your rules return setups true to your original idea. Day-to-day scanning (choosing the universe, reading results, saving scans) is covered by the dedicated guide "How to run a market scan", linked at the bottom of this page.

Step 5: iterate on your rules

A screener is rarely well calibrated on the first try. Two classic situations and their remedies:

• Too many results: your rules are too loose. Tighten the thresholds (RSI below 35 instead of 40), add a confirming condition (volume above its average), or shrink the universe.
• Zero results: your rules are too strict, or the setup you are looking for simply is not present in the market right now. Widen the thresholds, use a validity window of a few candles, or accept the wait : zero results is information too.

Step 6: automate with an autoscan

Once the screener is validated, there is no need to re-run it by hand. Create an autoscan: it automatically re-runs your screener at every candle close on the relevant timeframe, and sends you an e-mail alert as soon as assets match. Your strategy watches the market for you, even when you are away from the screen : the step that turns an analysis tool into a monitoring system.

One last piece of advice: before trading your screener's signals, run it through a backtest to measure how its signals would have performed historically, then practice in paper trading. A screener tells you where to look; backtesting and simulation tell you whether it is worth acting on.