diff --git a/runTests.sh b/runTests.sh
index 18846d9..c0fc3ee 100755
--- a/runTests.sh
+++ b/runTests.sh
@@ -5,5 +5,7 @@ set -eu
 SCRIPT_DIR="$(cd -- "$(dirname -- "$0")" && pwd)"
 cd "$SCRIPT_DIR"
 
+export TYPECHECKING=1
+
 ${JQ:-jq} -n -r -L tool -L . "include \"testLib\"; testLibMain"
 ${JQ:-jq} -n -r -L tool -L . "include \"tests\"; testsMain"
\ No newline at end of file
diff --git a/tool/main.jq b/tool/main.jq
index a878f68..9d311b1 100644
--- a/tool/main.jq
+++ b/tool/main.jq
@@ -3,6 +3,8 @@
 include "utils";
 include "argsLib";
 include "journalUtils";
+import "types" as types;
+import "typeLib" as typeLib;
 
 def printExperienceStats($stats; $substanceFilter; $consumerFilter; $withTitle):
   . as $experience |
@@ -249,7 +251,8 @@ def main($ARGS):
       ""
     ] | join("\n") | halt_error(1);
 
-  . as $exportData | 
+  . as $exportData |
+  $exportData | types::ensureExportData |
 
   ($ARGS | parseArgs) as $parsedArgs |
 
diff --git a/tool/tests.jq b/tool/tests.jq
index 6cadd79..e351d5c 100644
--- a/tool/tests.jq
+++ b/tool/tests.jq
@@ -1,8 +1,9 @@
 import "./testdata/tests_export" as $exportData;
 include "journalUtils";
 include "testLib";
+import "typeLib" as typeLib;
 
-def testsMain:
+def journalUtilsTests:
   expectPassed(runTest(
     "invalid input to experienceByTitle";
     (
@@ -10,4 +11,9 @@ def testsMain:
     );
     . == "experienceByTitle takes a array of experiences as input";
     true
-  )) | "Tests Passed\n" | halt_error(0);
+  ));
+
+def testsMain:
+  journalUtilsTests | 
+  typeLib::typeLibTests |
+  "Tests Passed\n" | halt_error(0);
diff --git a/tool/typeLib.jq b/tool/typeLib.jq
new file mode 100644
index 0000000..dd5e80a
--- /dev/null
+++ b/tool/typeLib.jq
@@ -0,0 +1,56 @@
+include "testLib";
+
+def typecheckingEnabled:
+  if $ENV["TYPECHECKING"] != null and (["1", "true", "on"] | any(index($ENV["TYPECHECKING"]))) then
+    true
+  else false end;
+
+def typecheckingDebug:
+  if $ENV["TYPECHECKING_DEBUG"] != "" and $ENV["TYPECHECKING_DEBUG"] != null then
+    true
+  else false end;
+
+def typeErrorText:
+  . as $type |
+  "Type Error Checking '\($type)'";
+def typeErrorText($type): $type | typeErrorText;
+
+def typeError($type):
+  if typecheckingDebug then debug({$type, value: .}) end |
+  error($type | typeErrorText);
+
+def ensureNull: if typecheckingEnabled and (. | type != "null") then typeError("null") end;
+def ensureBool: if typecheckingEnabled and (. | type) != "boolean" then typeError("bool") end;
+def ensureString: if typecheckingEnabled and (. | type) != "string" then typeError("string") end;
+def ensureArray: if typecheckingEnabled and (. | type) != "array" then typeError("array") end;
+def ensureObject: if typecheckingEnabled and (. | type) != "object" then typeError("object") end;
+def ensureNumber: if typecheckingEnabled and (. | type) != "number" then typeError("number") end;
+
+def ensureNull($value): $value | ensureNull;
+def ensureBool($value): $value | ensureBool;
+def ensureString($value): $value | ensureString;
+def ensureArray($value): $value | ensureArray;
+def ensureObject($value): $value | ensureObject;
+def ensureNumber($value): $value | ensureNumber;
+
+def ensureNullOr(ensureType): 
+  if . == null then . else . | ensureType end;
+
+def ensureKey($type; $key): if (. | has($key) | not) then typeError("\($type):\($key)") end;
+def ensureKey($value; $type; $key): $value | ensureKey($type; $key);
+
+# TYPECHECKING=1 required for tests
+def typeLibTests:
+  expectPassed(runTest(
+    "null is null";
+    (null | ensureNull);
+    true;
+    false
+  )) |
+  expectPassed(runTest(
+    "boolean is not null";
+    (true | ensureNull);
+    (. == typeErrorText("null"));
+    true
+  ));
+
diff --git a/tool/types.jq b/tool/types.jq
new file mode 100644
index 0000000..6025b95
--- /dev/null
+++ b/tool/types.jq
@@ -0,0 +1,26 @@
+import "typeLib" as typeLib;
+
+def ensureExperience:
+  . as $experience |
+  typeLib::ensureObject |
+  
+  $experience |
+  typeLib::ensureKey("experience"; "title") | 
+  .title | typeLib::ensureString |
+
+  $experience |
+  typeLib::ensureKey("experience"; "text") | 
+  .text | typeLib::ensureString
+  
+  ;
+
+def ensureExportData:
+  . as $exportData |
+  if typeLib::typecheckingEnabled then
+    typeLib::ensureObject |
+    typeLib::ensureKey("exportData"; "customSubstances") |
+    typeLib::ensureKey("exportData"; "customUnits") |
+    typeLib::ensureKey("exportData"; "experiences") |
+    typeLib::ensureKey("exportData"; "substanceCompanions") |
+    (.experiences[] | ensureExperience)
+  end;
\ No newline at end of file