// A decision keeps its context.
+Was Maria trained on March 2?
++ {{ + corrected + ? "The corrected certificate starts March 5. The earlier belief is still in the record." + : "Dana saw a certificate starting March 1. That is the evidence her decision used." + }} +
+Triplex
+An embedded fact database · TypeScript + Effect
+An embedded fact database for TypeScript back-office systems.
-Every write records who made it, which versioned rules governed it, and when it was true. Audit questions and open work become queries instead of investigations.
+Facts change. Rules change. Your record of what happened shouldn’t.
+Triplex keeps facts, time, and versioned rules together. Every write records who acted, which rules applied, and when it was true. Audit questions and open work become queries instead of investigations.
+ + +Pre-1.0 · MIT licensed · In-memory + SQLite supported
PostgreSQL is a production candidate · Current state ↗
Pre-1.0 · Built on Effect 4 (effect@4.0.0-rc.112; Effect 3 is not compatible) · In-memory and SQLite supported · PostgreSQL is a production candidate · Maturity contract
The problem
+00 / The missing context
An auditor asks: was Maria trained for the Harbor site on the day she started there? In a typical stack, the evidence is spread across systems that never shared an identity model or a clock.
One scenario, start to finish
+01 / One scenario, start to finish
Maria is trained for Harbor from March 1 to June 1 and placed there on March 2 under release hr-2026.1. The rules then change: hr-2026.2 requires a supervisor on every placement. Later, an auditor finds that the certificate actually began on March 5.
After the scenario runs, the database’s own journal reads:
+Every snippet is type-checked. Every output is produced by running this scenario in CI. The database’s own journal reads:
Three questions, three queries
+02 / Three questions, three queries
Each answer below is the real output of the code beside it.
Derived work
+03 / Derived work
Most back-office bugs come down to a task that should exist but doesn’t, or one that exists but shouldn’t. Event handlers create work one step at a time and drift out of sync with the data. A derivation states what should be true, and reconciliation reports the difference.
Modeling
+04 / Modeling
Most back-office systems are built from the same parts. This is where each part goes.
Deployment
+05 / Deployment
Triplex runs inside your process as Effect layers. Switching storage changes the layer you provide, and the rest of the program stays the same. On PostgreSQL, Triplex can share your application’s transaction, so your own rows, Triplex facts, the journal, and an outbox row commit or roll back together.
Fit
+06 / Fit
07 / Part of the WorldVM family
+Small experiments in software you can inspect, explain, and build on. Triplex keeps the facts. These projects explore the language and models around them.
+