What Is a Stock Screener?
Stock screener is a tool that filters a universe of listed companies down to those meeting stated numerical conditions, such as size, volume, valuation or price relative to an average. It narrows a field to a shortlist, and because you write the conditions, the shortlist reflects your assumptions.
Covered on this page: Finviz and TradingView.
A screener answers exactly one question: which stocks currently match this description? Everything useful and everything dangerous about the tool follows from who writes the description.
How it works
Start with a universe. Every US-listed stock, or a market, or an index — the set you are willing to consider at all.
Apply conditions. Market cap above a number, average volume above another, price above a moving average, a valuation ratio below a threshold.
What survives is the shortlist. Not the best stocks — the ones matching conditions you specified, which is a different claim.
Why the filters matter more than the tool
Every screener applies the conditions faithfully. They differ in data coverage and interface, not in whether they correctly execute a filter.
So the tool is not the variable. Two people with the same screener and different filters get completely different lists, and the difference is entirely in what they asked for.
Which makes “best screener settings” a strange phrase. Best for what holding period, what account size, what market? A setting is only best relative to a purpose somebody stated.
A worked example
Eight thousand tickers. Add market cap above 2 billion: a few thousand remain. Add average volume above a million shares: fewer still.
Two filters have done most of the work, and neither is clever. They removed the names where the spread and the slippage would exceed any edge the idea had.
Now add a technical condition and you are at a few dozen — a list a person can read in ten minutes.
Add six more and you are at three names. Those three satisfy a very specific description of the past, and the specificity came from you rather than from the market.
The two filters that earn their place
Average volume. On this site’s shared series a round trip costs 0.0098, about 2% of the median bar range of 0.493 — and that is a liquid-market figure. In a thin stock the real spread is a multiple of it, and the spread is paid on every trade whether the idea works or not.
Market capitalisation. Smaller companies have wider spreads, thinner books and larger gaps, so a size floor is a liquidity filter wearing different clothes.
Everything else is preference. Valuation ratios, technical conditions, sector exclusions — all reasonable, none as consequential as making sure you can get in and out at a sane price.
Which is the unglamorous conclusion. Most screening advice concerns the interesting filters, and most of the benefit comes from the boring two.
The original data
On this site’s shared series: median bar range 0.493, ninetieth percentile 1.101, largest bar 2.338. Direction runs average 2.01 bars with a longest of 11. A round trip costs 0.0098, about 2% of the median bar.
The run figures explain why a screen is not a signal. A filter identifies a condition that already holds; whether the next move continues is a separate question, and in a series turning every two bars the answer is usually no.
And this site’s fee measurement shows where small costs end up: 75 basis points a year removes 20.2% of a thirty-year balance. A spread paid on every screened name you act on is the same arithmetic, faster.
Screening without fooling yourself
Write the filters before looking at results. Adjusting conditions until the list contains names you already liked is not screening, it is confirmation with extra steps.
Keep the screen fixed for a period. A saved screen run weekly produces a comparable series of outputs; one edited each week produces nothing you can learn from.
Record what you did with the output. Screens are testable — did the names you took actually behave differently from the ones you skipped? — and almost nobody checks.
And accept that a screen cannot tell you why. It knows a company’s price is above an average; it does not know the company is under investigation, has lost a contract, or is about to report. That part is reading, and the screen exists to make the reading list short enough to do.
Fundamental screens versus technical ones
A fundamental screen filters on company facts - revenue growth, margins, debt, valuation ratios. Those update only when a company reports, so the screen’s answers change four times a year rather than daily.
A technical screen filters on price and volume behaviour - above an average, near a high, unusual volume. Those change every session, so the same screen returns a different list each morning.
They answer different questions and are often combined badly. A screen mixing quarterly fundamentals with a daily price condition is asking about two timescales at once, and the fast condition drives almost all of the turnover in the list.
The cleaner approach is sequencing. Use fundamentals to build a universe you would be willing to own, then use technicals to decide when to look at it - rather than requiring both to be true on the same morning.
When it fails
The characteristic failure is filtering until the answer is comfortable. The list comes back at two hundred names, which feels like too much work, so conditions are added — each defensible in isolation — until five names remain. Those five now match an extremely specific description of what already happened, and the tightening was driven by wanting a shorter list rather than by any belief about what matters. A screen narrowed for convenience is fitted to the past just as surely as one narrowed by backtesting.
A second failure is screening without a liquidity floor, which fills the list with names that are expensive to trade.
A third is treating the output as recommendations. It is a reading list.
A fourth is changing the filters weekly, which destroys any ability to judge whether they work.
And a fifth is assuming the data is current. Free tiers are usually delayed, and fundamentals update only when a company reports.
Related
Finviz covers the screener most people start with. Liquidity covers why the volume filter matters most. And build a watchlist covers what to do with the shortlist.
A screener does not find opportunities. It finds stocks matching a description you wrote, which means the quality of the output is entirely the quality of the description. Most people spend their time on exotic filters when the two that matter are size and volume.
— Michael Whitman, from this video
This page is educational, not financial advice. Test every idea on your own charts before risking money. Some links on this page earn a commission if you buy through them. It costs you nothing and it does not decide what appears here or in what order — how these pages are made is set out in our methodology.