diff --git a/vidformer-cli/src/bench.rs b/vidformer-cli/src/bench.rs
index 1a4be79..eac3bcb 100644
--- a/vidformer-cli/src/bench.rs
+++ b/vidformer-cli/src/bench.rs
@@ -3,7 +3,7 @@ use glob::glob;
 use serde::Deserialize;
 use std::collections::BTreeMap;
 use std::sync::Arc;
-use vidformer::run_spec;
+use vidformer::run;
 
 #[derive(Deserialize)]
 struct DveBench {
@@ -69,11 +69,11 @@ pub(crate) fn cmd_benchmark(opt: &BenchmarkCmd) {
 
         println!("Running spec {} benches", entry.display());
         for _i in 0..opt.warmup_runs {
-            run_spec(&spec, "/tmp/output.mp4", &context, &config, &None).unwrap();
+            run(&spec, "/tmp/output.mp4", &context, &config, &None).unwrap();
         }
 
         for i in 0..opt.runs {
-            let stat = run_spec(&spec, "/tmp/output.mp4", &context, &config, &None).unwrap();
+            let stat = run(&spec, "/tmp/output.mp4", &context, &config, &None).unwrap();
 
             let benchmark_stat = BenchmarkStat {
                 bench: entry.display().to_string(),
diff --git a/vidformer-cli/src/main.rs b/vidformer-cli/src/main.rs
index 600e5c1..1cc4101 100644
--- a/vidformer-cli/src/main.rs
+++ b/vidformer-cli/src/main.rs
@@ -2,7 +2,7 @@ use clap::{Parser, Subcommand};
 use num_rational::Rational64;
 use std::{collections::BTreeMap, fs::File, io::Write};
 
-use vidformer::{filter, run_spec, sir, source, spec};
+use vidformer::{filter, run, sir, source, spec};
 
 mod bench;
 mod yrden;
@@ -177,7 +177,7 @@ fn cmd_x() {
     let dve_config = std::sync::Arc::new(dve_config);
 
     println!("Running spec...");
-    let stats = run_spec(&spec, output_path, &context, &dve_config, &None).unwrap();
+    let stats = run(&spec, output_path, &context, &dve_config, &None).unwrap();
 
     dbg!(&stats);
 
diff --git a/vidformer-cli/src/yrden.rs b/vidformer-cli/src/yrden.rs
index 755b31b..0397f82 100644
--- a/vidformer-cli/src/yrden.rs
+++ b/vidformer-cli/src/yrden.rs
@@ -382,6 +382,7 @@ async fn yrden_http_req(
                 serde_json::from_reader(spec_content).expect("Unable to parse JSON");
 
             let spec: Box<dyn spec::Spec> = Box::new(spec);
+            let spec = std::sync::Arc::new(spec);
             let mut filters = crate::default_filters();
 
             for (name, filter) in request.filters {
@@ -423,18 +424,34 @@ async fn yrden_http_req(
             };
             let dve_config = std::sync::Arc::new(dve_config);
 
+            // Validate the spec
+            let validation_status = vidformer::validate(&spec, &context, &dve_config);
+            if let Err(err) = validation_status {
+                return Ok(hyper::Response::builder()
+                    .status(hyper::StatusCode::BAD_REQUEST)
+                    .header("Access-Control-Allow-Origin", "*")
+                    .body(http_body_util::Full::new(hyper::body::Bytes::from(
+                        format!("Error validating spec: {}", err),
+                    )))
+                    .unwrap());
+            }
+
             let host_prefix = {
                 let global: std::sync::MutexGuard<'_, YrdenGlobal> = global.lock().unwrap();
                 global.host_prefix.clone()
             };
 
-            let (namespace_id, playlist, stream, ranges) =
-                vidformer::create_spec_hls(spec.as_ref(), &host_prefix, &context, &dve_config);
+            let (namespace_id, playlist, stream, ranges) = vidformer::create_spec_hls(
+                spec.as_ref().as_ref(),
+                &host_prefix,
+                &context,
+                &dve_config,
+            );
 
             let namespace = YrdenNamespace {
                 context,
                 dve_config,
-                spec: std::sync::Arc::new(spec),
+                spec,
                 playlist,
                 stream,
                 ranges,
@@ -625,7 +642,7 @@ async fn yrden_http_req(
             let spec = std::sync::Arc::new(spec);
 
             let spec_result = tokio::task::spawn_blocking(move || {
-                vidformer::run_spec(&spec, &output_path2, &context, &dve_config, &None)
+                vidformer::run(&spec, &output_path2, &context, &dve_config, &None)
             })
             .await
             .unwrap();
@@ -748,7 +765,7 @@ async fn yrden_http_req(
 
             // todo, don't unwrap
             let spec_result = tokio::task::spawn_blocking(move || {
-                vidformer::run_spec(
+                vidformer::run(
                     &spec,
                     &tmp_path_2,
                     &context,
@@ -847,7 +864,7 @@ async fn yrden_http_req(
 
             // todo, don't unwrap
             let spec_result = tokio::task::spawn_blocking(move || {
-                vidformer::run_spec(
+                vidformer::run(
                     &spec,
                     &tmp_path_2,
                     &context,
diff --git a/vidformer/src/dve.rs b/vidformer/src/dve.rs
index b780b5f..dc54c64 100644
--- a/vidformer/src/dve.rs
+++ b/vidformer/src/dve.rs
@@ -1040,8 +1040,8 @@ impl ExecContext {
     }
 }
 
-/// Execute a vidformer spec
-pub fn run_spec(
+/// Execute a spec, or a range of a spec.
+pub fn run(
     spec: &Arc<Box<dyn Spec>>,
     output_path: &str,
     context: &Arc<Context>,
@@ -1117,6 +1117,31 @@ pub fn run_spec(
     exec_contex.run()
 }
 
+/// Validate that a spec can be run.
+pub fn validate(
+    spec: &Arc<Box<dyn Spec>>,
+    context: &Arc<Context>,
+    config: &Arc<Config>,
+) -> Result<(), Error> {
+    let expected_output_type = config.expected_output_type();
+
+    let process_span = Arc::new(crate::sir::ProcessSpan::create(
+        spec.as_ref().as_ref(),
+        context,
+        &None,
+    ));
+
+    // Type check frames
+    for oframe in &process_span.frames {
+        let frame_type = type_frame(context, config, oframe)?;
+        if frame_type != expected_output_type {
+            return Err(Error::InvalidOutputFrameType);
+        }
+    }
+
+    Ok(())
+}
+
 fn encoder_thread(
     config: Arc<Config>,
     stat: Arc<StatRunner>,
diff --git a/vidformer/src/lib.rs b/vidformer/src/lib.rs
index 4c20e99..8300d12 100644
--- a/vidformer/src/lib.rs
+++ b/vidformer/src/lib.rs
@@ -11,6 +11,7 @@ mod pool;
 mod util;
 
 pub use dve::{
-    create_spec_hls, run_spec, Config, Context, EncoderConfig, Error, Range, RangeTsFormat, Stats,
+    create_spec_hls, run, validate, Config, Context, EncoderConfig, Error, Range, RangeTsFormat,
+    Stats,
 };
 pub use util::{codecs, init, CodecDescriptor};
diff --git a/vidformer/tests/basic_tests.rs b/vidformer/tests/basic_tests.rs
index 3b7a4e0..b631670 100644
--- a/vidformer/tests/basic_tests.rs
+++ b/vidformer/tests/basic_tests.rs
@@ -115,7 +115,7 @@ fn test_placeholder() {
     let spec = std::sync::Arc::new(spec);
     let context = std::sync::Arc::new(context);
     let dve_config = std::sync::Arc::new(dve_config);
-    let stats = run_spec(&spec, output_path, &context, &dve_config, &None).unwrap();
+    let stats = run(&spec, output_path, &context, &dve_config, &None).unwrap();
     assert_eq!(stats.max_decoder_count, 0);
     assert_eq!(stats.frames_written, 24 * 3);
 
@@ -169,7 +169,7 @@ fn test_bad_resolution() {
     let context = std::sync::Arc::new(context);
     let dve_config = std::sync::Arc::new(dve_config);
     assert!(matches!(
-        run_spec(
+        run(
             &spec,
             test_output_path!(test_bad_resolution),
             &context,
@@ -227,7 +227,7 @@ fn test_non_existant_source() {
     let context = std::sync::Arc::new(context);
     let dve_config = std::sync::Arc::new(dve_config);
 
-    let ret = run_spec(
+    let ret = run(
         &spec,
         test_output_path!(test_non_existant_source),
         &context,
@@ -299,7 +299,7 @@ fn test_no_source_file() {
     let context = std::sync::Arc::new(context);
     let dve_config = std::sync::Arc::new(dve_config);
 
-    let ret = run_spec(
+    let ret = run(
         &spec,
         test_output_path!(test_non_existant_source),
         &context,
@@ -371,7 +371,7 @@ fn test_tos_transcode_1dec() {
         num_frames: NUM_FRAMES,
     }));
     let output_path = test_output_path!(test_tos_transcode_1dec);
-    let stats = run_spec(&spec, output_path, &context, &dve_config, &None).unwrap();
+    let stats = run(&spec, output_path, &context, &dve_config, &None).unwrap();
 
     assert_eq!(stats.max_decoder_count, 1);
     assert_eq!(stats.frames_written, NUM_FRAMES as usize);
@@ -400,7 +400,7 @@ fn test_tos_transcode_2dec() {
         num_frames: NUM_FRAMES,
     }));
     let output_path = test_output_path!(test_tos_transcode_2dec);
-    let stats = run_spec(&spec, output_path, &context, &dve_config, &None).unwrap();
+    let stats = run(&spec, output_path, &context, &dve_config, &None).unwrap();
 
     assert!(stats.max_decoder_count >= 1 && stats.max_decoder_count <= 2);
     assert_eq!(stats.frames_written, NUM_FRAMES as usize);
@@ -429,7 +429,7 @@ fn test_tos_transcode_4dec() {
         num_frames: NUM_FRAMES,
     }));
     let output_path = test_output_path!(test_tos_transcode_4dec);
-    let stats = run_spec(&spec, output_path, &context, &dve_config, &None).unwrap();
+    let stats = run(&spec, output_path, &context, &dve_config, &None).unwrap();
 
     assert!(stats.max_decoder_count >= 1 && stats.max_decoder_count <= 4);
     assert_eq!(stats.frames_written, NUM_FRAMES as usize);
@@ -458,7 +458,7 @@ fn test_tos_transcode_manydec() {
         num_frames: NUM_FRAMES,
     }));
     let output_path = test_output_path!(test_tos_transcode_manydec);
-    let stats = run_spec(&spec, output_path, &context, &dve_config, &None).unwrap();
+    let stats = run(&spec, output_path, &context, &dve_config, &None).unwrap();
 
     assert!(stats.max_decoder_count >= 1 && stats.max_decoder_count <= 100);
     assert_eq!(stats.frames_written, NUM_FRAMES as usize);
@@ -486,7 +486,7 @@ fn test_tos_transcode_1dec_1pool() {
     let spec: std::sync::Arc<Box<dyn spec::Spec>> =
         std::sync::Arc::new(Box::new(ClipSpec { num_frames: 2 * 24 })); // make sure we only need one source GOP
     let output_path = test_output_path!(test_tos_transcode_1dec_1pool);
-    let stats = run_spec(&spec, output_path, &context, &dve_config, &None).unwrap();
+    let stats = run(&spec, output_path, &context, &dve_config, &None).unwrap();
 
     assert_eq!(stats.max_decoder_count, 1);
     assert_eq!(stats.decoders_created, 1); // this is just a basic streaming edit. if our algorithm works it should just decode the one needed GOP