Change the rule once.Everything follows along.
In most software, a business rule lives in many places at once: the database, the server, the app, the documentation. When the rule changes, someone has to find every copy and update it by hand, and sooner or later the copies disagree. Here the rule is written once, in a rulebook, and every file is generated from it. Press play below and watch one small rule, the way a greeting is worded, change in seven generated files, a spreadsheet and a running app at the same time.
Every line of code on screen was copied from a real run of the effortless command line: effortless -init, one install per generator, a build after each change, and a round trip through Excel.
How to read it
One thing, one color, everywhere it appears.
A fact someone typed in. The Name column, and every place a file refers to it: {{Name}} in the rulebook, tc.Name in Go, ?name in OWL, cell B3 in Excel, the input box in the app.
The rule's own words, "Hello " and "!!!". The same purple in the rulebook, in all seven generated files, and in the Excel formula.
A value the rule worked out, like Hello Bob!!!. Nobody types it. It is computed from the name and the rule.
Each card shows only the line that computes the greeting, slid sideways so the rule sits on the dashed line. The wheel keeps four files in front and turns to show the rest.
Two kinds of change
A fact changes one value. A rule changes every file, together.
Rename Bob to Bobby and rebuild, and only Bob's greeting changes. None of the seven generated files is touched, because a name is a fact, and facts are data.
Change the wording of the greeting and rebuild, and every greeting changes. Python, Go, TypeScript, PostgreSQL, C#, OWL and the plain-English RuleSpeak® are all rewritten in the same build, so they can never disagree.
The hub is a role
Change it wherever you work.
The rulebook is the Single Source of Truth because it is the hub that is currently authorized to be authoritative, not because the file is special. The Excel workbook is generated from it, and it can also write back: change the formula in Excel, import it with xlsx-to-rulebook, and one build carries the change out to every other file.
Or just ask Claude in plain English. It edits the rule, runs the build, and the rulebook, all seven files and the app follow along.