What the Rules step does
The Rules step derives new values from data your flow already has. You give it facts — a flat object of inputs — and rules — an object saying what to calculate from them. It works out the order to evaluate in and returns a flat object of results for the rest of the flow to use. It is closest in spirit to a set of spreadsheet formulas: each rule names the value it produces, and rules that depend on one another sort themselves out. Use it when the logic is a calculation or a decision made from values you already have — pricing and discount bands, eligibility checks, validating a submission, scoring, working out a due date, or picking a label. Reach for the Eval step instead when you need real code, and for the Condition step when the outcome is which branch of the flow runs next.A first example
Facts@fact:. Operators
nest — the or takes two comparisons as its inputs. And the key on the left is
just a name you chose; it becomes a fact that later rules can read.
A worked example
A discount band, the discount it implies, and the resulting price. FactsdiscountRate.value is an if/else ladder: cells are tried in order and the first
matching condition wins, with the last cell as the default. The two rules below
it reference it by name, and the engine works out that they must run after it.
What to know before you build one
Some failures are silent
A misspelled operator fails the step and names itself. A ladder that matches
nothing, a calculation that produces
NaN and an outcome of null do not —
the fact is simply absent and the flow carries on.Dots in rule names need brackets
A rule named
finalPrice.value is read downstream as
$.rules_1['finalPrice.value']. The dotted form resolves to nothing.The operator list is fixed
The engine has 96 registered operator names — many of them aliases of each
other — plus
fact. Anything outside that list does not exist, however
reasonable it sounds.Publish before testing
Editing a flow changes its draft. A running flow keeps using the published
version until you publish again.
Where to go next
Getting Started
Build and test a rule end to end.
Core Concepts
The rule shapes, evaluation order, defaults, wildcards and failure modes.
Operations Reference
Every operator, with an executed example.
Common Patterns
Worked solutions to the problems that come up repeatedly.
Variable Mapping
How
$. expressions pull facts in from earlier steps.Rules Step
Configuring the step in the flow editor.