Screener attach

Also seen as: In and Out screeners, entry screener / exit screener, Qualify and Reject (the two pools' labels), Attach to In / Attach to Out

What do the two screener pools do?

The qualifying pool decides who is considered, and the rejecting pool decides who is thrown out — the app states each rule where the pool is: "Instruments must match an In screener to be considered." and "Instruments matching any Out screener are excluded."

Within a pool, membership is any, not all: the pool header reads "Match any" with the count of screeners in it, so an instrument that matches one qualifying screener is a candidate even if it fails the others, and an instrument that matches one rejecting screener is out even if it fails the others. Filters inside a single screener still combine with AND — see matches.

The two pools are only available together in Compose; the other asset-selection modes carry a single screener with no rejecting pool.

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:

where: $S$ is the set of instruments the strategy may hold at that rebalance; $Q_i$ is the set of instruments in the working scope that match the $i$-th qualifying screener; $R_j$ is the set that match the $j$-th rejecting screener; $n$ and $m$ are how many screeners sit in each pool; the working scope is the basket if it has instruments in it, and the whole market otherwise; and when $n = 0$ the first union is the whole working scope, because nothing is narrowing it.

Union (∪) is why "Match any" behaves the way it does inside a pool, and set difference (∖) is why one rejecting match is enough to remove an instrument no matter how many qualifying screeners liked it.

Worked example

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:

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 cap applies on top: with the cap at 5, the strategy holds five of the seven rather than all of them. At the next rebalance the same three screeners are re-evaluated and the seven can be a different seven.

Does editing the saved screener change strategies that already use it?

No — attaching copies the screener's filters into the strategy at that moment, so a later edit to the saved screener in your library does not reach strategies that already have it attached. Each attachment is its own copy: you edit that copy's filters from inside the strategy, and the change affects only that strategy, never your library screener or another strategy that attached the same one. This is the same copy-on-use rule that governs Duplicate and Copy to Mine.

Fincanva does remember which library screener an attachment came from, but only to support one manual, one-directional action: Update source screener pushes the strategy's copy back onto the saved screener, overwriting its filters and universe. Nothing pushes the other way. When the attachment has no library origin — one inserted empty, or one whose original was deleted — the option is unavailable and reads "No source screener tracked — use Save as new instead".

Defaults in Fincanva

• An attached screener is shown by name with its filter count, and can be opened and edited without detaching it.
• Adding a second screener to a pool widens that pool, because a pool matches on any of its screeners — it does not tighten it the way adding a filter to one screener does.
• A rejecting screener with no qualifying screener leaves the working scope as the candidate set and only subtracts from it; Fincanva flags that case as something to check rather than blocking it — see strategy alerts.
• A strategy on the screener path needs at least one attached screener before it can be saved and run: "Add at least 1 screener."
• The full step-by-step is in Attaching a screener to a strategy.