diff --git a/src/main/kotlin/org/idiosapps/ExceptionHelper.kt b/src/main/kotlin/org/idiosapps/ExceptionHelper.kt
index 805226e..7ddf00e 100644
--- a/src/main/kotlin/org/idiosapps/ExceptionHelper.kt
+++ b/src/main/kotlin/org/idiosapps/ExceptionHelper.kt
@@ -16,6 +16,8 @@ class ExceptionHelper {
                 return getExceptionMessage(XETEX)
             } else if (exception.toString().contains(PDFTEX)) {
                 return getExceptionMessage(PDFTEX)
+            } else if (exception.toString().contains("Input")) {
+                return exception.message.toString() // Exception already contains missing input file info
             } else {
                 // log out start of stacktrace - should help with any Exception
                 exception.printStackTrace()
diff --git a/src/main/kotlin/org/idiosapps/FXMLController.kt b/src/main/kotlin/org/idiosapps/FXMLController.kt
index 2b4b20a..5b8390d 100644
--- a/src/main/kotlin/org/idiosapps/FXMLController.kt
+++ b/src/main/kotlin/org/idiosapps/FXMLController.kt
@@ -14,10 +14,12 @@ class FXMLController {
     @FXML
     fun buildButtonClicked() {
 
-        try { // first check dependencies - have a good idea of what to expect
+        try { // first check dependencies & inputs - have a good idea of what to expect
             OSUtils.hasProgram(PDFTEX)
             OSUtils.hasProgram(XETEX)
-            buildGradedReader() // our pipeline for building our graded reader!
+            Filenames.checkInputs()
+
+            buildGradedReader() // use our pipeline for building our graded reader!
         } catch (exception: Exception) {
             exception.printStackTrace()
 
@@ -36,8 +38,6 @@ class FXMLController {
     private fun buildGradedReader() {
         var languageUsed = "mandarin"
 
-        val filenames = Filenames() // load defaults from class
-
         var vocabArray: ArrayList<String> = ArrayList() // This is a list of all the input vocabulary
         var vocabComponentArray: ArrayList<ArrayList<String>> =
             ArrayList() // This an [array of [arrays containing input vocab split into parts]]
@@ -50,16 +50,16 @@ class FXMLController {
 
 
         OSUtils.tryMakeOutputDir() // Java will only make a new file if the parent folder exists (on Windows anyway)
-        val outputStoryTeXWriter = PrintWriter(filenames.outputStoryFilename, "UTF-8")
+        val outputStoryTeXWriter = PrintWriter(Filenames.outputStoryFilename, "UTF-8")
 
-        VocabUtils.splitVocabIntoParts(filenames.inputVocabFilename, vocabArray, vocabComponentArray)
-        VocabUtils.splitVocabIntoParts(filenames.inputKeyNamesFilename, keyNameArray, keyNameComponentArray)
+        VocabUtils.splitVocabIntoParts(Filenames.inputVocabFilename, vocabArray, vocabComponentArray)
+        VocabUtils.splitVocabIntoParts(Filenames.inputKeyNamesFilename, keyNameArray, keyNameComponentArray)
 
-        TexUtils.copyToTex(outputStoryTeXWriter, filenames.inputHeaderFilename)
-        TexUtils.copyToTex(outputStoryTeXWriter, filenames.inputTitleFilename)
-        TexUtils.copyToTex(outputStoryTeXWriter, filenames.inputStoryFilename)
+        TexUtils.copyToTex(outputStoryTeXWriter, Filenames.inputHeaderFilename)
+        TexUtils.copyToTex(outputStoryTeXWriter, Filenames.inputTitleFilename)
+        TexUtils.copyToTex(outputStoryTeXWriter, Filenames.inputStoryFilename)
 
-        SummaryPageWriter.writeVocabSection(outputStoryTeXWriter, filenames.inputVocabFilename, vocabComponentArray)
+        SummaryPageWriter.writeVocabSection(outputStoryTeXWriter, Filenames.inputVocabFilename, vocabComponentArray)
         // todo WriteSummaryPage.writeTexGrammar
 
         outputStoryTeXWriter.append("\\end{document}")
@@ -67,21 +67,21 @@ class FXMLController {
 
         PDFUtils.xelatexToPDF()
 
-        val pdfNumberOfPages = PDFUtils.getNumberOfPDFPages(filenames.outputPDFFilename)
-        PDFUtils.readPDF(filenames.outputPDFFilename, vocabComponentArray, pdfPageLastSentences, pdfNumberOfPages)
+        val pdfNumberOfPages = PDFUtils.getNumberOfPDFPages(Filenames.outputPDFFilename)
+        PDFUtils.readPDF(Filenames.outputPDFFilename, vocabComponentArray, pdfPageLastSentences, pdfNumberOfPages)
         TexUtils.getTexLineNumbers(
-            filenames.outputStoryFilename,
+            Filenames.outputStoryFilename,
             pdfPageLastSentences,
             texLinesOfPDFPagesLastSentences,
             texLineIndexOfPDFPageLastSentence
         )
 
-        TeXStyling.addStyling(vocabComponentArray, filenames.outputStoryFilename, SUPERSCRIPT_STYLING)
-        TeXStyling.addStyling(keyNameComponentArray, filenames.outputStoryFilename, UNDERLINE_STYLING)
+        TeXStyling.addStyling(vocabComponentArray, Filenames.outputStoryFilename, SUPERSCRIPT_STYLING)
+        TeXStyling.addStyling(keyNameComponentArray, Filenames.outputStoryFilename, UNDERLINE_STYLING)
 
         FooterUtils.addVocabFooters(
             vocabComponentArray,
-            filenames.outputStoryFilename,
+            Filenames.outputStoryFilename,
             texLinesOfPDFPagesLastSentences,
             languageUsed,
             pdfNumberOfPages,
diff --git a/src/main/kotlin/org/idiosapps/Filenames.kt b/src/main/kotlin/org/idiosapps/Filenames.kt
index 7c2af17..84cf9b3 100644
--- a/src/main/kotlin/org/idiosapps/Filenames.kt
+++ b/src/main/kotlin/org/idiosapps/Filenames.kt
@@ -1,17 +1,37 @@
 package org.idiosapps
 
+import java.io.File
+
 class Filenames {
-    val inputPrefix: String = "./input/"
-    val outputPrefix: String = "./output/"
+    companion object {
+        val inputPrefix: String = "./input/"
+        val outputPrefix: String = "./output/"
+
+        val inputHeaderFilename: String = inputPrefix + "header"
+        val inputTitleFilename: String = inputPrefix + "title"
+        val inputStoryFilename: String = inputPrefix + "story"
 
+        val inputVocabFilename: String = inputPrefix + "vocab"
+        val inputKeyNamesFilename: String = inputPrefix + "names"
 
-    val inputHeaderFilename: String = inputPrefix + "header"
-    val inputTitleFilename: String = inputPrefix + "title"
-    val inputStoryFilename: String = inputPrefix + "story"
+        val outputStoryFilename: String = outputPrefix + "outputStory.tex"
+        val outputPDFFilename: String = outputPrefix + "outputStory.pdf"
 
-    val inputVocabFilename: String = inputPrefix + "vocab"
-    val inputKeyNamesFilename: String = inputPrefix + "names"
+        fun checkInputs() {
+            val inputArray = arrayListOf(
+                inputHeaderFilename,
+                inputTitleFilename,
+                inputStoryFilename,
+                inputVocabFilename,
+                inputKeyNamesFilename
+            )
 
-    val outputStoryFilename: String = outputPrefix + "outputStory.tex"
-    val outputPDFFilename: String = outputPrefix + "outputStory.pdf"
+            for (input in inputArray) {
+                val inputFile = File(input)
+                if (!inputFile.exists()) { // could also check for size > 0 on required inputs
+                    throw Exception("Input does not exist: $input")
+                }
+            }
+        }
+    }
 }
\ No newline at end of file