diff --git a/lib/ai/formula_screen.dart b/lib/ai/formula_screen.dart
index 292d018..fe4757c 100644
--- a/lib/ai/formula_screen.dart
+++ b/lib/ai/formula_screen.dart
@@ -9,7 +9,7 @@ import 'unit_dropdown.dart';
 
 class FormulaScreen extends StatefulWidget {
   final Formula formula;
-  final UnitCorpus corpus;
+  final Corpus corpus;
 
   const FormulaScreen({
     super.key,
diff --git a/lib/ai/unit_dropdown.dart b/lib/ai/unit_dropdown.dart
index d13338e..830b250 100644
--- a/lib/ai/unit_dropdown.dart
+++ b/lib/ai/unit_dropdown.dart
@@ -3,7 +3,7 @@ import '../../formula_models.dart';
 import '../../corpus.dart';
 
 class UnitDropdown extends StatelessWidget {
-  final UnitCorpus corpus;
+  final Corpus corpus;
   final VariableSpec variable;
   final String? selectedUnit;
   final ValueChanged<String?> onUnitChanged;
@@ -19,7 +19,7 @@ class UnitDropdown extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final unitNames = corpus.unitsOfSameMagnitude(variable.unit);
-    final availableUnits = unitNames.map((name) => corpus.get(name)).toList();
+    final availableUnits = unitNames.map((name) => corpus.getUnit(name)).toList();
 
     return SizedBox(
       width: 200, // Constrain dropdown width
diff --git a/lib/ai/unit_list.dart b/lib/ai/unit_list.dart
index fad8749..8ca03ed 100644
--- a/lib/ai/unit_list.dart
+++ b/lib/ai/unit_list.dart
@@ -4,7 +4,7 @@ import '../formula_models.dart';
 import 'formula_screen.dart';
 
 class UnitList extends StatefulWidget {
-  final UnitCorpus corpus;
+  final Corpus corpus;
 
   const UnitList({super.key, required this.corpus});
 
diff --git a/lib/corpus.dart b/lib/corpus.dart
index 16ec384..2a13df5 100644
--- a/lib/corpus.dart
+++ b/lib/corpus.dart
@@ -22,12 +22,38 @@ class Multimap<K, V> extends DelegatingMap<K, List<V>> {
   }
 }
 
-class FormulaCorpus{
+class Corpus{
   final Multimap<String, Formula> _tags = Multimap.create();
   final Map<String, Formula> _allFormulas = {};
-}
 
-class UnitCorpus {
+  void loadFormulas(List<Formula> formulas, {bool replaceOnDuplicates = false, bool checkUnits = true}) {
+    for (final formula in formulas) {
+      if (!replaceOnDuplicates && _allFormulas.containsKey(formula.name)) {
+        throw ArgumentError("Duplicate formula:$formula");
+      }
+
+      if( checkUnits ){
+        for( final inputVar in formula.input + [formula.output] ){
+          if( getUnit(inputVar.unit) == null ){
+            throw ArgumentError( "Unit not found: ${inputVar.unit}");
+          }
+        }
+      }
+
+      _allFormulas[formula.name] = formula;
+      for( final tag in formula.tags ){
+        _tags[tag]?.add(formula);
+      }
+    }
+  }
+
+  List<Formula> getTagFormulas(String tag){
+    if( _tags[tag] == null ){
+      return [];
+    }
+    return _tags[tag]?.toList(growable:false) as List<Formula>;
+  }
+
   final Multimap<String, String> _baseToUnits = Multimap.create();
   final Map<String, UnitSpec> _allUnits = {};
 
@@ -42,19 +68,18 @@ class UnitCorpus {
   }
 
   List<String> unitsOfSameMagnitude(String unit){
-    final base = this[unit].baseUnit;
+    final base = getUnit(unit).baseUnit;
     return _baseToUnits[base] as List<String>;
   }
 
-  UnitSpec operator [](String unit) {
+
+  UnitSpec getUnit(String unit) {
     if (!_allUnits.containsKey(unit)) {
       throw ArgumentError("Unit not found:$unit");
     }
     return _allUnits.get(unit);
   }
 
-  UnitSpec get(String unit) => this[unit];
-
   String _converterFromCodeString(Number x, String codeString) {
     final buffer = StringBuffer();
     buffer.writeln("final x = ${x};");
@@ -64,7 +89,7 @@ class UnitCorpus {
   }
 
   Number _convertToBase(Number x, String fromUnit) {
-    final unit = this[fromUnit];
+    final unit = getUnit(fromUnit);
 
     if (unit.factorFromUnitToBase != null) {
       return x * (unit.factorFromUnitToBase as Number);
@@ -81,7 +106,7 @@ class UnitCorpus {
   }
 
   Number _convertFromBase(Number x, String toUnit) {
-    final unit = this[toUnit];
+    final unit = getUnit(toUnit);
 
     if (unit.factorFromUnitToBase != null) {
       return x / (unit.factorFromUnitToBase as Number);
@@ -105,4 +130,6 @@ class UnitCorpus {
   }
 
   Iterable<UnitSpec> allUnits() => _allUnits.values;
+
+
 }
diff --git a/lib/defaults/default_corpus.dart b/lib/defaults/default_corpus.dart
new file mode 100644
index 0000000..fffefd4
--- /dev/null
+++ b/lib/defaults/default_corpus.dart
@@ -0,0 +1,46 @@
+import 'dart:convert' show utf8;
+
+import 'package:resource_portable/resource_portable.dart' show Resource;
+
+import '../corpus.dart';
+import '../formula_models.dart';
+
+Future<Corpus> createDefaultCorpus() async{
+  final corpus = Corpus();
+
+  Future<void> loadUnits() async {
+    final unitResources = [
+      "lib/defaults/units/area.d4rt.units",
+      "lib/defaults/units/distance.d4rt.units",
+      "lib/defaults/units/energy.d4rt.units",
+      "lib/defaults/units/pressure.d4rt.units",
+      "lib/defaults/units/temperature.d4rt.units",
+      "lib/defaults/units/velocity.d4rt.units",
+      "lib/defaults/units/mass.d4rt.units",
+      "lib/defaults/units/angle.d4rt.units",
+    ];
+
+    for (final unitRes in unitResources) {
+      final resource = Resource(unitRes);
+      final literal = await resource.readAsString(encoding: utf8);
+      final units = UnitSpec.fromArrayStringLiteral(literal);
+      corpus.loadUnits(units);
+    }
+  }
+
+  Future<void> loadFormulas() async {
+    final formulaResources = ["lib/defaults/formulas.d4rt"];
+
+    for (final formRes in formulaResources) {
+      final resource = Resource(formRes);
+      final literal = await resource.readAsString(encoding: utf8);
+      final formulas = Formula.fromArrayStringLiteral(literal);
+      corpus.loadFormulas(formulas);
+    }
+  }
+
+  await loadUnits();
+  await loadFormulas();
+
+  return corpus;
+}
diff --git a/lib/defaults/formulas.d4rt b/lib/defaults/formulas.d4rt
new file mode 100644
index 0000000..c3f7a48
--- /dev/null
+++ b/lib/defaults/formulas.d4rt
@@ -0,0 +1,109 @@
+[
+  // Free fall distance (vertical)
+  {
+    "name": "Free Fall Distance",
+    "description": '''
+Calculates vertical displacement under constant gravity
+
+`h = ½gt²`
+
+Where:
+- `g` = Gravitational acceleration (9.81 m/s² on Earth)
+- `t` = Time in free fall (seconds)
+
+![Free Fall Diagram](https://upload.wikimedia.org/wikipedia/commons/thumb/7/72/Free-fall.svg/1200px-Free-fall.svg.png)''',
+    "input": [
+      {"name": "t", "unit": "second"},  // Time in seconds
+      {"name": "g", "unit": "m/s²"}  // Gravitational acceleration
+    ],
+    "output": {"name": "h", "unit": "m"},  // Height in meters
+    "d4rtCode": "h = 0.5 * g * pow(t, 2)",
+    "tags": ["physics", "kinematics"]
+  },
+  
+  // Newton's Law of Universal Gravitation
+  {
+    "name": "Gravitational Force",
+    "description": '''
+Newton's law of universal gravitation
+
+`F = G(m₁m₂)/r²`
+
+Where:
+- `G` = Gravitational constant (6.674×10⁻¹¹ N·m²/kg²)
+- `m₁`, `m₂` = Masses of two objects
+- `r` = Distance between centers of masses
+
+![Gravitation](https://upload.wikimedia.org/wikipedia/commons/thumb/3/33/NewtonsLawOfUniversalGravitation.svg/1200px-NewtonsLawOfUniversalGravitation.svg.png)''',
+    "input": [
+      {"name": "m1", "unit": "kg"},  // Mass 1
+      {"name": "m2", "unit": "kg"},  // Mass 2
+      {"name": "r", "unit": "m"}     // Distance between masses
+    ],
+    "output": {"name": "F", "unit": "N"},  // Force in newtons
+    "d4rtCode": "F = (6.67430e-11 * m1 * m2) / pow(r, 2)",
+    "tags": ["physics", "astronomy", "gravity"]
+  },
+  
+  // Kinetic Energy
+  {
+    "name": "Kinetic Energy",
+    "description": '''
+Energy possessed by a moving object
+
+`KE = ½mv²`
+
+Where:
+- `m` = Mass of object
+- `v` = Velocity of object
+
+![Kinetic Energy](https://upload.wikimedia.org/wikipedia/commons/thumb/4/44/Kinetic_energy.svg/1200px-Kinetic_energy.svg.png)''',
+    "input": [
+      {"name": "m", "unit": "kg"},  // Mass
+      {"name": "v", "unit": "m/s"}  // Velocity
+    ],
+    "output": {"name": "KE", "unit": "J"},  // Energy in joules
+    "d4rtCode": "KE = 0.5 * m * pow(v, 2)",
+    "tags": ["physics", "energy", "mechanics"]
+  },
+  
+  // Projectile Motion Range
+  {
+    "name": "Projectile Range",
+    "description": "Calculates horizontal distance of projectile motion\n\n"
+                 "`R = (v² sin(2θ))/g`\n\n"
+                 "Where:\n"
+                 "- `v` = Initial velocity\n"
+                 "- `θ` = Launch angle\n"
+                 "- `g` = Gravitational acceleration\n\n"
+                 "![Projectile Motion](https://upload.wikimedia.org/wikipedia/commons/thumb/5/52/Projectile_motion_diagram.png/800px-Projectile_motion_diagram.png)",
+    "input": [
+      {"name": "v", "unit": "m/s"},  // Initial velocity
+      {"name": "θ", "unit": "deg"}   // Launch angle
+    ],
+    "output": {"name": "R", "unit": "m"},  // Horizontal distance
+    "d4rtCode": "R = (pow(v, 2) * sin(2 * radians(θ))) / 9.80665",
+    "tags": ["physics", "kinematics", "projectile"]
+  },
+
+  {
+    "name": "Newton's Second Law",
+    "description": '''
+Force equals mass times acceleration
+
+`F = m * a`
+
+Where:
+- `m` = Mass of object (kg)
+- `a` = Acceleration (m/s²)
+
+![Newton's Second Law](https://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Newtonslawsofmotion.jpg/800px-Newtonslawsofmotion.jpg)''',
+    "input": [
+      {"name": "m", "unit": "kg"},  // Mass
+      {"name": "a", "unit": "m/s²"} // Acceleration
+    ],
+    "output": {"name": "F", "unit": "N"},  // Force in newtons
+    "d4rtCode": "F = m * a",
+    "tags": ["physics", "mechanics", "newton"]
+  },
+]
diff --git a/lib/units/angle.d4rt.units b/lib/defaults/units/angle.d4rt.units
similarity index 100%
rename from lib/units/angle.d4rt.units
rename to lib/defaults/units/angle.d4rt.units
diff --git a/lib/units/area.d4rt.units b/lib/defaults/units/area.d4rt.units
similarity index 100%
rename from lib/units/area.d4rt.units
rename to lib/defaults/units/area.d4rt.units
diff --git a/lib/units/distance.d4rt.units b/lib/defaults/units/distance.d4rt.units
similarity index 100%
rename from lib/units/distance.d4rt.units
rename to lib/defaults/units/distance.d4rt.units
diff --git a/lib/units/energy.d4rt.units b/lib/defaults/units/energy.d4rt.units
similarity index 100%
rename from lib/units/energy.d4rt.units
rename to lib/defaults/units/energy.d4rt.units
diff --git a/lib/units/mass.d4rt.units b/lib/defaults/units/mass.d4rt.units
similarity index 100%
rename from lib/units/mass.d4rt.units
rename to lib/defaults/units/mass.d4rt.units
diff --git a/lib/units/pressure.d4rt.units b/lib/defaults/units/pressure.d4rt.units
similarity index 100%
rename from lib/units/pressure.d4rt.units
rename to lib/defaults/units/pressure.d4rt.units
diff --git a/lib/units/temperature.d4rt.units b/lib/defaults/units/temperature.d4rt.units
similarity index 100%
rename from lib/units/temperature.d4rt.units
rename to lib/defaults/units/temperature.d4rt.units
diff --git a/lib/units/velocity.d4rt.units b/lib/defaults/units/velocity.d4rt.units
similarity index 100%
rename from lib/units/velocity.d4rt.units
rename to lib/defaults/units/velocity.d4rt.units
diff --git a/lib/formula_models.dart b/lib/formula_models.dart
index 5d38601..dd75a82 100644
--- a/lib/formula_models.dart
+++ b/lib/formula_models.dart
@@ -196,8 +196,8 @@ class Formula {
   factory Formula.fromSet(Map<Object?, Object?> theSet) {
     VariableSpec parseVar(Map<Object?, Object?> varSpec) {
       String name = SetUtils.stringValue(varSpec, "name");
-      String magnitude = SetUtils.stringValue(varSpec, "magnitude");
-      return VariableSpec(name: name, unit: magnitude);
+      String unit = SetUtils.stringValue(varSpec, "unit");
+      return VariableSpec(name: name, unit: unit);
     }
 
     String name = SetUtils.stringValue(theSet, "name");
diff --git a/lib/formulas.d4rt b/lib/formulas.d4rt
deleted file mode 100644
index c5e3913..0000000
--- a/lib/formulas.d4rt
+++ /dev/null
@@ -1,109 +0,0 @@
-[
-  // Free fall distance (vertical)
-  {
-    name: "Free Fall Distance",
-    description: '''
-Calculates vertical displacement under constant gravity
-
-`h = ½gt²`
-
-Where:
-- `g` = Gravitational acceleration (9.81 m/s² on Earth)
-- `t` = Time in free fall (seconds)
-
-![Free Fall Diagram](https://upload.wikimedia.org/wikipedia/commons/thumb/7/72/Free-fall.svg/1200px-Free-fall.svg.png)''',
-    input: [
-      {name: "t", unit: "s"},  // Time in seconds
-      {name: "g", unit: "m/s²"}  // Gravitational acceleration
-    ],
-    output: {name: "h", unit: "m"},  // Height in meters
-    d4rtCode: "h = 0.5 * g * pow(t, 2)",
-    tags: ["physics", "kinematics"]
-  },
-  
-  // Newton's Law of Universal Gravitation
-  {
-    name: "Gravitational Force",
-    description: '''
-Newton's law of universal gravitation
-
-`F = G(m₁m₂)/r²`
-
-Where:
-- `G` = Gravitational constant (6.674×10⁻¹¹ N·m²/kg²)
-- `m₁`, `m₂` = Masses of two objects
-- `r` = Distance between centers of masses
-
-![Gravitation](https://upload.wikimedia.org/wikipedia/commons/thumb/3/33/NewtonsLawOfUniversalGravitation.svg/1200px-NewtonsLawOfUniversalGravitation.svg.png)''',
-    input: [
-      {name: "m1", unit: "kg"},  // Mass 1
-      {name: "m2", unit: "kg"},  // Mass 2
-      {name: "r", unit: "m"}     // Distance between masses
-    ],
-    output: {name: "F", unit: "N"},  // Force in newtons
-    d4rtCode: "F = (6.67430e-11 * m1 * m2) / pow(r, 2)",
-    tags: ["physics", "astronomy", "gravity"]
-  },
-  
-  // Kinetic Energy
-  {
-    name: "Kinetic Energy",
-    description: '''
-Energy possessed by a moving object
-
-`KE = ½mv²`
-
-Where:
-- `m` = Mass of object
-- `v` = Velocity of object
-
-![Kinetic Energy](https://upload.wikimedia.org/wikipedia/commons/thumb/4/44/Kinetic_energy.svg/1200px-Kinetic_energy.svg.png)''',
-    input: [
-      {name: "m", unit: "kg"},  // Mass
-      {name: "v", unit: "m/s"}  // Velocity
-    ],
-    output: {name: "KE", unit: "J"},  // Energy in joules
-    d4rtCode: "KE = 0.5 * m * pow(v, 2)",
-    tags: ["physics", "energy", "mechanics"]
-  },
-  
-  // Projectile Motion Range
-  {
-    name: "Projectile Range",
-    description: "Calculates horizontal distance of projectile motion\n\n"
-                 "`R = (v² sin(2θ))/g`\n\n"
-                 "Where:\n"
-                 "- `v` = Initial velocity\n"
-                 "- `θ` = Launch angle\n"
-                 "- `g` = Gravitational acceleration\n\n"
-                 "![Projectile Motion](https://upload.wikimedia.org/wikipedia/commons/thumb/5/52/Projectile_motion_diagram.png/800px-Projectile_motion_diagram.png)",
-    input: [
-      {name: "v", unit: "m/s"},  // Initial velocity
-      {name: "θ", unit: "deg"}   // Launch angle
-    ],
-    output: {name: "R", unit: "m"},  // Horizontal distance
-    d4rtCode: "R = (pow(v, 2) * sin(2 * radians(θ))) / 9.80665",
-    tags: ["physics", "kinematics", "projectile"]
-  },
-
-  {
-    name: "Newton's Second Law",
-    description: '''
-Force equals mass times acceleration
-
-`F = m * a`
-
-Where:
-- `m` = Mass of object (kg)
-- `a` = Acceleration (m/s²)
-
-![Newton's Second Law](https://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Newtonslawsofmotion.jpg/800px-Newtonslawsofmotion.jpg)''',
-    input: [
-      {name: "m", unit: "kg"},  // Mass
-      {name: "a", unit: "m/s²"} // Acceleration
-    ],
-    output: {name: "F", unit: "N"},  // Force in newtons
-    d4rtCode: "F = m * a",
-    tags: ["physics", "mechanics", "newton"]
-  },
-]
diff --git a/lib/main.dart b/lib/main.dart
index 6c3dd83..f67246c 100644
--- a/lib/main.dart
+++ b/lib/main.dart
@@ -6,11 +6,12 @@ import 'dart:convert';
 
 import 'ai/unit_list.dart';
 import 'corpus.dart';
+import 'defaults/default_corpus.dart';
 
 void main() {
   runApp(MaterialApp(
-    home: FutureBuilder<UnitCorpus>(
-      future: createTestCorpus(),
+    home: FutureBuilder<Corpus>(
+      future: createDefaultCorpus(),
       builder: (context, snapshot) {
         if (snapshot.connectionState == ConnectionState.done) {
           if (snapshot.hasError) {
@@ -24,31 +25,6 @@ void main() {
   ));
 }
 
-Future<UnitCorpus> createTestCorpus() async {
-  final corpus = UnitCorpus();
-  final resources = [
-    "lib/units/area.d4rt.units",
-    "lib/units/distance.d4rt.units",
-    "lib/units/energy.d4rt.units",
-    "lib/units/pressure.d4rt.units",
-    "lib/units/temperature.d4rt.units",
-    "lib/units/velocity.d4rt.units",
-    "lib/units/mass.d4rt.units",
-    "lib/units/angle.d4rt.units"
-  ];
-  
-  for (final resourcePath in resources) {
-    try {
-      final resource = Resource(resourcePath);
-      final literal = await resource.readAsString(encoding: utf8);
-      final units = UnitSpec.fromArrayStringLiteral(literal);
-      corpus.loadUnits(units);
-    } catch (e) {
-      print('Error loading $resourcePath: $e');
-    }
-  }
-  return corpus;
-}
 
 class MyApp extends StatelessWidget {
   const MyApp({super.key});
diff --git a/test/formula_models_test.dart b/test/formula_models_test.dart
index 52d6fea..666c895 100644
--- a/test/formula_models_test.dart
+++ b/test/formula_models_test.dart
@@ -1,4 +1,5 @@
 import 'package:d4rt_formulas/corpus.dart';
+import 'package:d4rt_formulas/defaults/default_corpus.dart';
 import 'package:d4rt_formulas/formula_evaluator.dart';
 import 'package:test/test.dart';
 import 'package:d4rt_formulas/formula_models.dart';
@@ -8,16 +9,8 @@ import 'package:resource_portable/resource.dart' show Resource;
 
 void main() {
 
-  Future<UnitCorpus> createTestCorpus() async {
-    final corpus = UnitCorpus();
-    final resources = ["lib/units/distance.d4rt.units", "lib/units/temperature.d4rt.units"];
-    for( final r in resources ) {
-      final resource = Resource(r);
-      final literal = await resource.readAsString(encoding: utf8);
-      final units = UnitSpec.fromArrayStringLiteral(literal);
-      corpus.loadUnits(units);
-    }
-    return corpus;
+  Future<Corpus> createTestCorpus() async {
+    return createDefaultCorpus();
   }
 
   test("Parses unit", () {