diff --git a/README.md b/README.md
index 0559ece..6df093c 100644
--- a/README.md
+++ b/README.md
@@ -15,7 +15,7 @@ and bash, you might do something like this:
       ffmpeg -i /tmp/my/source.mp4 -ss ${i} -t $((i+INCR)) /tmp/my/slice_${i}_$((i+INCR)).mp4
     done
 ```
-With JVCL, you'd write this spec file:
+With JVCL, you'd write this spec file and save it to a file (for example `my-spec.jvcl`):
 ```json
 {
   "assets": [ {"name": "src", "path": "/tmp/my/source.mp4"} ],
@@ -31,7 +31,7 @@ With JVCL, you'd write this spec file:
 ```
 and then run it like this:
 ```shell script
-jvcl my-spec.json
+jvcl my-spec.jvcl
 ```
 Yes, the JVCL is longer, but I think many would agree it is easier to read and maintain.
 
@@ -67,16 +67,40 @@ Unlike most JSON, comments *are* allowed in JVCL spec files:
 * A line comment starts with `//` and continue to the end of the line
 * A multi-line block syntax starts with `/*` and ends with `*/`
 
+### Executing a JVCL Spec
+To execute a spec stored in the file `my-spec.json`, you would run:
+```shell script
+jvcl my-spec.jvcl
+```
+
+#### Scratch Directory
+Output assets will be placed in the scratch directory, unless otherwise specified
+in the spec file. By default, JVCL will create a new temporary directory to use as the scratch
+directory. You can set the scratch directory explicitly using the `-t` or `--temp-dir` option:
+
+```shell script
+jvcl -t /some/tempdir my-spec.json
+```
+
+#### Command Help
+To view a list of all `jvcl` command-line options, run `jvcl -h` or `jvcl --help`
+
 ## Assets
-Assets are the inputs: generally image, audio and video files. Assets have a name and a path.
+Assets are your media files: generally image, audio and video files.
 
-The path can be a file or a URL.
+All assets have a name and a path.
 
 Input assets are defined using the `assets` array of a JVCL spec.
 
-Operations produce one or more assets, as specified in the `creates` property of
+For input assets, the path can be a file or a URL. URL-based assets will be downloaded
+to the scratch directory. This can be overridden using the `dest` property on the asset.
+
+Operations produce one or more output assets, as specified in the `creates` property of
 an operation JSON object.
 
+For output assets, the path will be within the scratch directory.
+You can override this using the `dest` property on the `creates` object associated with the operation.
+
 ### Asset Properties
 Assets expose properties that can be referenced in operations. The properties currently exposed are:
 
diff --git a/src/main/java/jvcl/main/JvclOptions.java b/src/main/java/jvcl/main/JvclOptions.java
index 2c6a076..5be5512 100644
--- a/src/main/java/jvcl/main/JvclOptions.java
+++ b/src/main/java/jvcl/main/JvclOptions.java
@@ -5,6 +5,7 @@ import lombok.Getter;
 import lombok.Setter;
 import lombok.extern.slf4j.Slf4j;
 import org.cobbzilla.util.main.BaseMainOptions;
+import org.kohsuke.args4j.Argument;
 import org.kohsuke.args4j.Option;
 
 import java.io.File;
@@ -19,10 +20,8 @@ import static org.cobbzilla.util.json.JsonUtil.json;
 @Slf4j
 public class JvclOptions extends BaseMainOptions {
 
-    public static final String USAGE_SPEC = "Spec file to run. Default is to read from stdin.";
-    public static final String OPT_SPEC = "-f";
-    public static final String LONGOPT_SPEC = "--file";
-    @Option(name=OPT_SPEC, aliases=LONGOPT_SPEC, usage=USAGE_SPEC)
+    public static final String USAGE_SPEC = "Spec file to run. Set to '-' to read from stdin.";
+    @Argument(usage=USAGE_SPEC, required=true)
     @Getter @Setter private File specFile;
 
     public JSpec getSpec() {
diff --git a/src/test/java/javicle/test/BasicTest.java b/src/test/java/javicle/test/BasicTest.java
index e7bd91d..559c29a 100644
--- a/src/test/java/javicle/test/BasicTest.java
+++ b/src/test/java/javicle/test/BasicTest.java
@@ -6,21 +6,30 @@ import org.junit.Test;
 
 import java.io.File;
 
-import static jvcl.main.JvclOptions.LONGOPT_SPEC;
+import static org.apache.commons.lang3.exception.ExceptionUtils.getStackTrace;
+import static org.cobbzilla.util.daemon.ZillaRuntime.shortError;
 import static org.cobbzilla.util.io.FileUtil.abs;
 import static org.cobbzilla.util.io.StreamUtil.loadResourceAsStream;
 import static org.cobbzilla.util.io.StreamUtil.stream2file;
+import static org.junit.Assert.fail;
 
 public class BasicTest {
 
-    @Test public void testSplit  () { runSpec("tests/test_split.json"); }
-    @Test public void testConcat () { runSpec("tests/test_concat.json"); }
-    @Test public void testTrim   () { runSpec("tests/test_trim.json"); }
-    @Test public void testOverlay() { runSpec("tests/test_overlay.json"); }
+    @Test public void testSplitConcatAndTrim  () {
+        runSpec("tests/test_split.jvcl");
+        runSpec("tests/test_concat.jvcl");
+        runSpec("tests/test_trim.jvcl");
+    }
+
+    // @Test public void test4Overlay() { runSpec("tests/test_overlay.jvcl"); }
 
     private void runSpec(String specPath) {
-        @Cleanup("delete") final File specFile = stream2file(loadResourceAsStream(specPath));
-        Jvcl.main(new String[]{LONGOPT_SPEC, abs(specFile)});
+        try {
+            @Cleanup("delete") final File specFile = stream2file(loadResourceAsStream(specPath));
+            Jvcl.main(new String[]{abs(specFile)});
+        } catch (Exception e) {
+            fail("runSpec("+specPath+") failed: "+shortError(e)+"\n"+getStackTrace(e));
+        }
     }
 
 }
diff --git a/src/test/resources/tests/test_concat.json b/src/test/resources/tests/test_concat.jvcl
similarity index 100%
rename from src/test/resources/tests/test_concat.json
rename to src/test/resources/tests/test_concat.jvcl
diff --git a/src/test/resources/tests/test_overlay.json b/src/test/resources/tests/test_overlay.jvcl
similarity index 98%
rename from src/test/resources/tests/test_overlay.json
rename to src/test/resources/tests/test_overlay.jvcl
index 2b7d0d1..adf037f 100644
--- a/src/test/resources/tests/test_overlay.json
+++ b/src/test/resources/tests/test_overlay.jvcl
@@ -18,7 +18,6 @@
         "name": "overlay1",
         "dest": "src/test/resources/outputs/overlay/"
       },
-      "perform": {
         "source": "vid1",              // main video asset
         "overlay": "vid2",             // overlay this video on the main video
 
diff --git a/src/test/resources/tests/test_split.json b/src/test/resources/tests/test_split.jvcl
similarity index 100%
rename from src/test/resources/tests/test_split.json
rename to src/test/resources/tests/test_split.jvcl
diff --git a/src/test/resources/tests/test_trim.json b/src/test/resources/tests/test_trim.jvcl
similarity index 100%
rename from src/test/resources/tests/test_trim.json
rename to src/test/resources/tests/test_trim.jvcl