diff --git a/packages/squiggle-lang/__tests__/FunctionRegistry_test.res b/packages/squiggle-lang/__tests__/FunctionRegistry_test.res
index e976f7b1..47d3005a 100644
--- a/packages/squiggle-lang/__tests__/FunctionRegistry_test.res
+++ b/packages/squiggle-lang/__tests__/FunctionRegistry_test.res
@@ -15,38 +15,40 @@ module FooImplementation = {
   open FunctionRegistry_Core
   open FunctionRegistry_Helpers
 
-  let library = [
-    Function.make(
-      ~name="add",
-      ~nameSpace="Foo",
-      ~definitions=[
-        FnDefinition.make(
-          ~requiresNamespace=false,
-          ~name="add",
-          ~inputs=[FRTypeNumber, FRTypeNumber],
-          ~run=(_, inputs, _) =>
-            switch inputs {
-            | [FRValueNumber(a), FRValueNumber(b)] => Ok(Wrappers.evNumber(a +. b))
-            | _ => Error("False")
-            },
-          (),
-        ),
-        FnDefinition.make(
-          ~requiresNamespace=true,
-          ~name="add",
-          ~inputs=[FRTypeNumber, FRTypeNumber, FRTypeNumber],
-          ~run=(_, inputs, _) =>
-            switch inputs {
-            | [FRValueNumber(a), FRValueNumber(b), FRValueNumber(c)] =>
-              Ok(Wrappers.evNumber(a +. b +. c))
-            | _ => Error("False")
-            },
-          (),
-        ),
-      ],
-      (),
-    ),
-  ]
+  let fn = Function.make(
+    ~name="add",
+    ~nameSpace="Foo",
+    ~examples=["Foo.add(1, 2)", "Foo.add(1, 2, 3)"],
+    ~output=EvtNumber,
+    ~definitions=[
+      FnDefinition.make(
+        ~requiresNamespace=false,
+        ~name="add",
+        ~inputs=[FRTypeNumber, FRTypeNumber],
+        ~run=(_, inputs, _) =>
+          switch inputs {
+          | [FRValueNumber(a), FRValueNumber(b)] => Ok(Wrappers.evNumber(a +. b))
+          | _ => Error("False")
+          },
+        (),
+      ),
+      FnDefinition.make(
+        ~requiresNamespace=true,
+        ~name="add",
+        ~inputs=[FRTypeNumber, FRTypeNumber, FRTypeNumber],
+        ~run=(_, inputs, _) =>
+          switch inputs {
+          | [FRValueNumber(a), FRValueNumber(b), FRValueNumber(c)] =>
+            Ok(Wrappers.evNumber(a +. b +. c))
+          | _ => Error("False")
+          },
+        (),
+      ),
+    ],
+    (),
+  )
+
+  let library = [fn]
 }
 
 let makeBindings = (previousBindings: Bindings.t): Bindings.t =>
@@ -75,8 +77,19 @@ describe("Module", () => {
     let result = evalToStringResultWithFoo("Foo.add(1,2,3)")
     expect(result)->toEqual("Ok(6)")
   })
-  test("add(1,2,3,5)", () => {
-    let result = evalToStringResultWithFoo("Foo.add(1,2,3,5)")
-    expect(result)->toEqual("Ok(6)")
+})
+
+describe("Fn auto-testing", () => {
+  let items = FooImplementation.fn.examples->E.A.to_list
+
+  testAll("tests of validity", items, r => {
+    expect(r->evalWithFoo->E.R.isOk)->toEqual(true)
+  })
+
+  testAll("tests of type", items, r => {
+    let responseType =
+      r->evalWithFoo->E.R2.fmap(ReducerInterface_InternalExpressionValue.valueToValueType)
+    let expectedOutputType = FooImplementation.fn.output |> E.O.toExn("")
+    expect(responseType)->toEqual(Ok(expectedOutputType))
   })
 })
\ No newline at end of file
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
index e0ef4441..d2d2a080 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Core.res
@@ -1,4 +1,5 @@
 type internalExpressionValue = ReducerInterface_InternalExpressionValue.t
+type internalExpressionValueType = ReducerInterface_InternalExpressionValue.internalExpressionValueType
 
 /*
   Function Registry "Type". A type, without any other information.
@@ -54,6 +55,7 @@ type function = {
   name: string,
   definitions: array<fnDefinition>,
   nameSpace: string,
+  output: option<internalExpressionValueType>,
   examples: array<string>,
   description: option<string>,
   isExperimental: bool,
@@ -374,6 +376,7 @@ module Function = {
     ~nameSpace,
     ~definitions,
     ~examples=?,
+    ~output=?,
     ~description=?,
     ~isExperimental=false,
     (),
@@ -381,6 +384,7 @@ module Function = {
     name: name,
     nameSpace: nameSpace,
     definitions: definitions,
+    output: output,
     examples: examples |> E.O.default([]),
     isExperimental: isExperimental,
     description: description,
diff --git a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Library.res b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Library.res
index 1d74f451..6543cbc9 100644
--- a/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Library.res
+++ b/packages/squiggle-lang/src/rescript/FunctionRegistry/FunctionRegistry_Library.res
@@ -55,7 +55,7 @@ module PointSet = {
 
   let library = [
     Function.make(
-      ~name="PointSet.makeContinuous",
+      ~name="makeContinuous",
       ~nameSpace,
       ~definitions=[
         FnDefinition.make(
@@ -69,7 +69,7 @@ module PointSet = {
       (),
     ),
     Function.make(
-      ~name="PointSet.makeDiscrete",
+      ~name="makeDiscrete",
       ~nameSpace,
       ~definitions=[
         FnDefinition.make(
@@ -89,7 +89,7 @@ module Functionn = {
   let nameSpace = "Function"
   let library = [
     Function.make(
-      ~name="Function.declare",
+      ~name="declare",
       ~nameSpace,
       ~description="Adds metadata to a function of the input ranges. Works now for numeric and date inputs. This is useful when making predictions. It allows you to limit the domain that your prediction will be used and scored within.",
       ~examples=[
@@ -177,7 +177,7 @@ module DistributionCreation = {
 
   let library = [
     Function.make(
-      ~name="Normal",
+      ~name="normal",
       ~nameSpace,
       ~examples=["normal(5,1)", "normal({p5: 4, p95: 10})", "normal({mean: 5, stdev: 2})"],
       ~definitions=[
@@ -190,7 +190,7 @@ module DistributionCreation = {
       (),
     ),
     Function.make(
-      ~name="Lognormal",
+      ~name="lognormal",
       ~nameSpace,
       ~examples=[
         "lognormal(0.5, 0.8)",
@@ -210,14 +210,14 @@ module DistributionCreation = {
       (),
     ),
     Function.make(
-      ~name="Uniform",
+      ~name="uniform",
       ~nameSpace,
       ~examples=[`uniform(10, 12)`],
       ~definitions=[TwoArgDist.make("uniform", twoArgs(SymbolicDist.Uniform.make))],
       (),
     ),
     Function.make(
-      ~name="Beta",
+      ~name="beta",
       ~nameSpace,
       ~examples=[`beta(20, 25)`, `beta({mean: 0.39, stdev: 0.1})`],
       ~definitions=[
@@ -227,28 +227,28 @@ module DistributionCreation = {
       (),
     ),
     Function.make(
-      ~name="Cauchy",
+      ~name="cauchy",
       ~nameSpace,
       ~examples=[`cauchy(5, 1)`],
       ~definitions=[TwoArgDist.make("cauchy", twoArgs(SymbolicDist.Cauchy.make))],
       (),
     ),
     Function.make(
-      ~name="Gamma",
+      ~name="gamma",
       ~nameSpace,
       ~examples=[`gamma(5, 1)`],
       ~definitions=[TwoArgDist.make("gamma", twoArgs(SymbolicDist.Gamma.make))],
       (),
     ),
     Function.make(
-      ~name="Logistic",
+      ~name="logistic",
       ~nameSpace,
       ~examples=[`logistic(5, 1)`],
       ~definitions=[TwoArgDist.make("logistic", twoArgs(SymbolicDist.Logistic.make))],
       (),
     ),
     Function.make(
-      ~name="To (Distribution)",
+      ~name="to (distribution)",
       ~nameSpace,
       ~examples=[`5 to 10`, `to(5,10)`, `-5 to 5`],
       ~definitions=[
@@ -261,21 +261,21 @@ module DistributionCreation = {
       (),
     ),
     Function.make(
-      ~name="Exponential",
+      ~name="exponential",
       ~nameSpace,
       ~examples=[`exponential(2)`],
       ~definitions=[OneArgDist.make("exponential", SymbolicDist.Exponential.make)],
       (),
     ),
     Function.make(
-      ~name="Bernoulli",
+      ~name="bernoulli",
       ~nameSpace,
       ~examples=[`bernoulli(0.5)`],
       ~definitions=[OneArgDist.make("bernoulli", SymbolicDist.Bernoulli.make)],
       (),
     ),
     Function.make(
-      ~name="PointMass",
+      ~name="pointMass",
       ~nameSpace,
       ~examples=[`pointMass(0.5)`],
       ~definitions=[OneArgDist.make("pointMass", SymbolicDist.Float.makeSafe)],
@@ -333,61 +333,61 @@ module Number = {
 
   let library = [
     Function.make(
-      ~name="Floor",
+      ~name="floor",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("floor", Js.Math.floor_float)],
       (),
     ),
     Function.make(
-      ~name="Ceiling",
+      ~name="ceiling",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("ceil", Js.Math.ceil_float)],
       (),
     ),
     Function.make(
-      ~name="Absolute Value",
+      ~name="absolute value",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("abs", Js.Math.abs_float)],
       (),
     ),
     Function.make(
-      ~name="Exponent",
+      ~name="exponent",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("exp", Js.Math.exp)],
       (),
     ),
     Function.make(
-      ~name="Log",
+      ~name="log",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("log", Js.Math.log)],
       (),
     ),
     Function.make(
-      ~name="Log Base 10",
+      ~name="log base 10",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("log10", Js.Math.log10)],
       (),
     ),
     Function.make(
-      ~name="Log Base 2",
+      ~name="log base 2",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("log2", Js.Math.log2)],
       (),
     ),
     Function.make(
-      ~name="Round",
+      ~name="round",
       ~nameSpace,
       ~definitions=[NumberToNumber.make("round", Js.Math.round)],
       (),
     ),
     Function.make(
-      ~name="Sum",
+      ~name="sum",
       ~nameSpace,
       ~definitions=[ArrayNumberDist.make("sum", r => r->E.A.Floats.sum->Wrappers.evNumber->Ok)],
       (),
     ),
     Function.make(
-      ~name="Product",
+      ~name="product",
       ~nameSpace,
       ~definitions=[
         ArrayNumberDist.make("product", r => r->E.A.Floats.product->Wrappers.evNumber->Ok),
@@ -395,25 +395,25 @@ module Number = {
       (),
     ),
     Function.make(
-      ~name="Min",
+      ~name="min",
       ~nameSpace,
       ~definitions=[ArrayNumberDist.make("min", r => r->E.A.Floats.min->Wrappers.evNumber->Ok)],
       (),
     ),
     Function.make(
-      ~name="Max",
+      ~name="max",
       ~nameSpace,
       ~definitions=[ArrayNumberDist.make("max", r => r->E.A.Floats.max->Wrappers.evNumber->Ok)],
       (),
     ),
     Function.make(
-      ~name="Mean",
+      ~name="mean",
       ~nameSpace,
       ~definitions=[ArrayNumberDist.make("mean", r => r->E.A.Floats.mean->Wrappers.evNumber->Ok)],
       (),
     ),
     Function.make(
-      ~name="Geometric Mean",
+      ~name="geometric mean",
       ~nameSpace,
       ~definitions=[
         ArrayNumberDist.make("geomean", r => r->E.A.Floats.geomean->Wrappers.evNumber->Ok),
@@ -421,13 +421,13 @@ module Number = {
       (),
     ),
     Function.make(
-      ~name="Standard Deviation",
+      ~name="standard deviation",
       ~nameSpace,
       ~definitions=[ArrayNumberDist.make("stdev", r => r->E.A.Floats.stdev->Wrappers.evNumber->Ok)],
       (),
     ),
     Function.make(
-      ~name="Variance",
+      ~name="variance",
       ~nameSpace,
       ~definitions=[
         ArrayNumberDist.make("variance", r => r->E.A.Floats.stdev->Wrappers.evNumber->Ok),
@@ -435,7 +435,7 @@ module Number = {
       (),
     ),
     Function.make(
-      ~name="Sort",
+      ~name="sort",
       ~nameSpace,
       ~definitions=[
         ArrayNumberDist.make("sort", r =>
@@ -445,7 +445,7 @@ module Number = {
       (),
     ),
     Function.make(
-      ~name="Cumulative Sum",
+      ~name="cumulative sum",
       ~nameSpace,
       ~definitions=[
         ArrayNumberDist.make("cumsum", r =>
@@ -455,7 +455,7 @@ module Number = {
       (),
     ),
     Function.make(
-      ~name="Cumulative Prod",
+      ~name="cumulative prod",
       ~nameSpace,
       ~definitions=[
         ArrayNumberDist.make("cumprod", r =>
@@ -465,7 +465,7 @@ module Number = {
       (),
     ),
     Function.make(
-      ~name="Diff",
+      ~name="diff",
       ~nameSpace,
       ~definitions=[
         ArrayNumberDist.make("diff", r =>
@@ -665,7 +665,7 @@ module List = {
 
   let library = [
     Function.make(
-      ~name="List.make",
+      ~name="make",
       ~nameSpace,
       ~definitions=[
         //Todo: If the second item is a function with no args, it could be nice to run this function and return the result.
@@ -685,7 +685,7 @@ module List = {
       (),
     ),
     Function.make(
-      ~name="List.upTo",
+      ~name="upTo",
       ~nameSpace,
       ~definitions=[
         FnDefinition.make(
@@ -702,7 +702,7 @@ module List = {
       (),
     ),
     Function.make(
-      ~name="List.first",
+      ~name="first",
       ~nameSpace,
       ~definitions=[
         FnDefinition.make(
@@ -720,7 +720,7 @@ module List = {
       (),
     ),
     Function.make(
-      ~name="List.last",
+      ~name="last",
       ~nameSpace,
       ~definitions=[
         FnDefinition.make(
@@ -738,7 +738,7 @@ module List = {
       (),
     ),
     Function.make(
-      ~name="List.reverse",
+      ~name="reverse",
       ~nameSpace,
       ~definitions=[
         FnDefinition.make(