Logic

Real products have dependencies. The oak finish is not available on the large size. Choosing the glass door forces the frame to metal. Selecting engraving reveals a field for the text.

Logic is where you write those down, so your customer cannot build something you would have to refuse.

Rules

A rule has a condition and one or more effects. When the condition is true, the effects apply.

Conditions use the same editor as everything else in Composer, so you already know it from variants: a simple pairing for one thing, or nested groups when several conditions combine.

When a rule fires

Three choices, and picking the right one matters.

While matching keeps the effect applied for as long as the condition is true, and undoes it when it stops being true. This is what you want for showing, hiding and restricting things. An option that should be unavailable on large sizes should use this, so it comes back when the customer picks a smaller size.

On change fires once, at the moment something changes. Use it for actions that should happen and then be left alone, such as resetting a dependent choice when the customer switches material. You can name the specific controls that should trigger it.

On load fires once when the configurator opens, for setting up an initial state.

The distinction that catches people out is between while-matching and on-change. If an effect keeps reapplying when the customer tries to change something, it probably wants to be an edge trigger. If an effect sticks around after it should have stopped, it probably wants to be while-matching.

What a rule can do

Set a control's value, or reset it to its default. Use this to keep the configuration coherent when a choice invalidates another.

Show or enable a control, and the same for an individual option. This is the most common effect: hiding what does not apply and greying out what cannot be chosen. Disabling is often kinder than hiding, because the customer can see the option exists and understands why it is unavailable.

Show a message, so the customer knows why. A rule that silently removes a choice is confusing, while one that says "oak is not available above 200 cm" is helpful.

Override the minimum, maximum or step of a number or slider, so the available range narrows to what you can actually make in the chosen material.

Show or hide a 3D element, whether a model, a part, a marker, a dimension, a decal or a light.

Force a material variant or a colour or texture variant, which is how one choice can drive an appearance change somewhere else.

Run a script, on the plans that include scripting.

Not every effect works with every trigger, and Composer tells you inline when a combination does not make sense rather than letting you publish something broken.

The Overview

Alongside Rules there is an Overview, which is read-only and shows every condition in the whole configuration in one place. Not just rules, but the conditions on variants, on options, on markers, on everything.

This is the page to open when a configurator misbehaves and you cannot see why. It shows what is conditional and, during Play, which conditions are currently true.

Rules and option conditions together

You can put a condition directly on a control or an option, and you can write a rule that affects the same thing. Both are valid, and they serve different purposes.

Use a direct condition when the dependency is simple and belongs to that one option. Use a rule when the same condition drives several effects, or when the logic is complex enough that you want it written down in one readable place rather than scattered across twenty options.

When both apply to the same thing, the rule is the stronger statement. There is one guarantee worth knowing: a rule can take an option away, but it can never grant an option that its own condition denies. That protects you from a rule accidentally making something purchasable that you had deliberately restricted.

Keep it as simple as the product allows

Logic is the part of a configurator that grows without anyone deciding it should. Every rule interacts with every other rule, and a configurator with forty of them is genuinely hard to reason about.

Before adding a rule, check whether a condition directly on the option would do. Give rules names that say what they are for. And use the Overview periodically to see what you have accumulated.