---
title: "Screener attach"
description: "A screener attach embeds a screener inside a strategy so a rule picks its instruments. Qualifying pools add candidates; rejecting pools remove them."
canonical_url: "https://fincanva.com/glossary/screener-attach"
last_updated: "2026-10-07"
md_url: "https://fincanva.com/glossary/screener-attach.md"
---

# Screener attach

A screener attach is a [screener](/glossary/screener) embedded in a [strategy](/glossary/strategy) so that a rule, not a hand-picked list, decides what it may hold, re-evaluated at every [rebalance](/glossary/rebalance). It sits in a **qualifying** pool, which brings instruments in, or a **rejecting** pool, which takes them out. Attaching copies the screener, so later edits to the saved one do not reach it.

**Also seen as:** In and Out screeners, Qualify and Reject

## How do the qualifying and rejecting pools combine?

The candidate set is the union of what the qualifying screeners match, minus the union of what the rejecting screeners match:

$$
{S} = \left( \bigcup_{i=1}^{{n}} {Q_i} \right) \setminus \left( \bigcup_{j=1}^{{m}} {R_j} \right)
$$

where:

- the instruments the strategy may hold at this rebalance
- the instruments in the working scope that match the i-th qualifying screener
- how many screeners sit in the qualifying pool
- the instruments in the working scope that match the j-th rejecting screener
- how many screeners sit in the rejecting pool

In words: an [instrument](/glossary/instrument) is a candidate when it matches at least one qualifying screener and no rejecting one. The working scope is the basket if it holds instruments, and each qualifying screener's own [universe](/glossary/universe) otherwise. With no qualifying screener the candidates are the basket itself; with no basket either, the strategy has nothing to choose from and does not run.

## How does Fincanva handle it?

- **Attaching a screener to a strategy is not included on the Free plan.** Free attaches none — a screener still runs on its own there — while Starter attaches 1, Advanced 2, and Ultimate and Professional 8. See [what each plan includes](/docs/account-and-plan/what-each-plan-includes) and [How does the Free plan show screeners in a strategy?](#how-does-the-free-plan-show-screeners-in-a-strategy)
- Two cases run differently in the engine than the formula suggests — see [When does the engine depart from the formula?](#when-does-the-engine-depart-from-the-formula)
- A second screener in a pool widens the pool, because a pool matches on *any* of its screeners; a filter added inside one screener narrows it.
- A strategy on the screener path needs at least one attached screener before it can be saved and run: "Add at least 1 screener." How to attach one: [Attach a screener to a strategy](/docs/strategies/attach-a-screener-to-a-strategy).

## Which titles does an entry screener put into the positions?

The positions are filled from the qualifying screeners' result in its order, decided in two steps.

1. **The cap.** When more titles pass than six times [Max positions](/glossary/max-positions), the engine keeps only the most traded — highest average traded volume — in that order. The cap applies to all qualifying screeners together, not to each one.
2. **Your ordering row.** A **Highest / Lowest** row — "is among the highest 10", say — keeps the first N titles of its own order: it is how you decide which titles are preferred. Without one, the order is the cap's by traded volume or — under the cap — an internal order of the index, which is not a merit.

So an ordering row decides only when its last row keeps no more than six times Max positions. Two alerts to review on the Asset selection card say where you stand: "No rule decides which names enter", when a qualifying screener has no ordering row, and "The engine does not keep the top of your ranking", when the last ordering row keeps more than the cap. With a [Ranking-based](/glossary/ranking-based) Risk-On method the positions follow that method's own ranking, and both alerts stay silent.

With two or more qualifying screeners a title enters by passing any one, and the grey note "Passing any one of the screeners is enough to enter" says so: "A title enters if it passes at least one of the screeners, not all of them; to ask for both conditions, put them in the same screener."

## What does it look like in practice?

A strategy's basket holds ten tickers, so that basket is the working scope:

`AAPL · MSFT · NVDA · TSLA · JNJ · PFE · KO · WMT · XOM · GE`

Two screeners sit in the qualifying pool and one in the rejecting pool. Suppose at this rebalance they match:

| Pool | Screener | Matches |
|---|---|---|
| Qualify | $Q_1$ | JNJ · PFE · KO · WMT · XOM |
| Qualify | $Q_2$ | AAPL · MSFT · NVDA · TSLA |
| Reject | $R_1$ | TSLA · XOM |

The qualifying union $Q_1 \cup Q_2$ is nine tickers — everything except **GE**, which matched neither, so it is never a candidate. Subtracting $R_1$ removes **TSLA** (a candidate via $Q_2$) and **XOM** (a candidate via $Q_1$), leaving seven:

`AAPL · MSFT · NVDA · JNJ · PFE · KO · WMT`

Those seven are what the strategy may hold at this rebalance. A [**Max positions**](/glossary/max-positions) cap applies on top: with the cap at 5, the strategy holds five of the seven. At the next rebalance the same three screeners are re-evaluated and the seven can be a different seven.

## When does the engine depart from the formula?

In two cases, and each raises a [strategy alert](/glossary/strategy-alerts) to review. **The same screener in both pools**: a title that passes both is sold and bought back in the same rebalance, so the entry wins, unless a [reinvest delay](/glossary/reinvest-delay) of at least 1 month holds it out. **A rejecting pool over a basket with no qualifying screener**: the engine sells what matches it and buys the same instrument back in the same rebalance, because the candidates are always the basket and no wait applies there — so the pool changes nothing, and the alert reads "The exit screener changes nothing".

## How does the Free plan show screeners in a strategy?

Visible and marked, never hidden. On the **Asset selection** card, **Screen** and **Compose** keep their place, each with the plan's bars after its name — hovering them reads "Available from Starter" — and choosing one opens it as a switched-off preview: the surface with the starter screener filled in, where nothing can be changed or saved. Pressing the bars, or the key you are already previewing, opens the plan dialog — "Strategies with screeners are available from Starter" — and choosing **Basket** brings back what the strategy holds. The Basket's **Filters** are hidden on Free unless the strategy already holds a screener.

A strategy that holds one anyway — made on a paid plan, or copied — is kept intact, but its [backtest](/glossary/backtest) is refused before you press it; see [plan compliance](/glossary/plan-compliance#what-happens-to-a-strategy-with-a-screener-on-the-free-plan).

Fincanva is for education and illustration only. It is not personalised financial advice, and past or simulated results do not predict future ones. [Read the Terms Addendum](https://fincanva.com/terms/addendum#section-3)