diff --git a/src/fetch.cr b/src/fetch.cr
index 58b69a0..dd80dee 100644
--- a/src/fetch.cr
+++ b/src/fetch.cr
@@ -43,7 +43,10 @@ module Muse::Dl
 
       # TODO: Add validation for the downloaded file (should be PDF)
       Crest.get(url, max_redirects: 0, handle_errors: false, headers: headers) do |response|
-        # puts response.headers["Content-Type"]
+        if !response.success?
+          raise Muse::Dl::Errors::DownloadError.new("Error downloading chapter. HTTP response code: #{response.status}")
+        end
+
         content_type = response.headers["Content-Type"]
         if content_type.is_a? String
           if /html/.match content_type
@@ -59,7 +62,12 @@ module Muse::Dl
           end
         end
         File.open(tmp_pdf_file, "w") do |file|
-          IO.copy(response.body_io, file)
+          response_str = response.body
+          file << response_str
+          if file.size == 0
+            # puts response.headers
+            raise Muse::Dl::Errors::DownloadError.new("Error: downloaded chapter file size is zero. Response size was #{response_str.bytesize}")
+          end
         end
       end
 
diff --git a/src/muse-dl.cr b/src/muse-dl.cr
index 5ae80e5..fcce75d 100644
--- a/src/muse-dl.cr
+++ b/src/muse-dl.cr
@@ -65,14 +65,30 @@ module Muse::Dl
     def self.run(args : Array(String))
       parser = Parser.new(args)
 
+      delay_secs = 1
       input_list = parser.input_list
       if input_list
         File.each_line input_list do |url|
-          # TODO: Change this to nil
-          parser.reset_output_file
-          parser.url = url.strip
-          # Ask the download process to not quit the process, and return instead
-          Main.dl parser
+          begin
+            # TODO: Change this to nil
+            parser.reset_output_file
+            parser.url = url.strip
+            # Ask the download process to not quit the process, and return instead
+            Main.dl parser
+            if delay_secs >= 2
+              delay_secs /= 2
+            end
+          rescue ex : Muse::Dl::Errors::DownloadError
+            puts ex
+            puts "Download error. Skipping book: #{url}. Waiting for #{delay_secs} seconds before continuing."
+            # Sleep to prevent hammering the server.
+            sleep(delay_secs)
+            delay_secs *= 2
+          rescue ex
+            puts ex
+            puts "Non-download error. Skipping book: #{url}."
+            sleep(1)
+          end
         end
       elsif parser.url
         Main.dl parser
diff --git a/src/pdftk.cr b/src/pdftk.cr
index d62c500..6833b5f 100644
--- a/src/pdftk.cr
+++ b/src/pdftk.cr
@@ -28,14 +28,22 @@ module Muse::Dl
     def execute(args : Array(String))
       binary = @binary
       if binary
-        Process.run(binary, args)
+        status = Process.run(binary, args, output: STDOUT, error: STDERR)
+        if !status.success?
+          puts "pdftk command failed: #{binary} #{args.join(" ")}"
+        end
+        return status.success?
       end
     end
 
     def strip_first_page(input_file : String)
       output_pdf = File.tempfile("muse-dl-temp", ".pdf")
-      execute [input_file, "cat", "2-end", "output", output_pdf.path]
-      File.rename output_pdf.path, input_file
+      is_success = execute [input_file, "cat", "2-end", "output", output_pdf.path]
+      if is_success
+        File.rename output_pdf.path, input_file
+      else
+        raise Muse::Dl::Errors::PDFOperationError.new("Error stripping first page of chapter.")
+      end
     end
 
     def add_bookmark(input_file : String, title : String)
@@ -48,11 +56,15 @@ module Muse::Dl
       BookmarkPageNumber: 1
       END
       File.write(bookmark_text_file.path, bookmark_text)
-      execute [input_file, "update_info", bookmark_text_file.path, "output", output_pdf.path]
+      is_success = execute [input_file, "update_info", bookmark_text_file.path, "output", output_pdf.path]
 
       # Cleanup
       bookmark_text_file.delete
-      File.rename output_pdf.path, input_file
+      if is_success
+        File.rename output_pdf.path, input_file
+      else
+        raise Muse::Dl::Errors::PDFOperationError.new("Error adding bookmark metadata to chapter.")
+      end
     end
 
     def add_metadata(input_file : File, output_file : String, book : Book)
@@ -95,7 +107,10 @@ module Muse::Dl
       EOT
 
       File.write(metadata_text_file.path, text)
-      execute [input_file.path, "update_info_utf8", metadata_text_file.path, "output", output_file]
+      is_success = execute [input_file.path, "update_info_utf8", metadata_text_file.path, "output", output_file]
+      if !is_success
+        raise Muse::Dl::Errors::PDFOperationError.new("Error adding metadata to book.")
+      end
       metadata_text_file.delete
     end
 
@@ -111,9 +126,12 @@ module Muse::Dl
 
       chapter_files = chapter_ids.map { |id| Fetch.chapter_file_name(id, @tmp_file_path) }
       args = chapter_files + ["cat", "output", output_file.path]
-      execute args
+      is_success = execute args
 
       # TODO: Validate final file here
+      if !is_success
+        raise Muse::Dl::Errors::PDFOperationError.new("Error stitching chapters together.")
+      end
 
       return output_file
     end