diff --git a/src/client.rs b/src/client.rs
index ad7a23d..705e65f 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -342,17 +342,7 @@ where
         params: JsonValue,
         options: SpawnOptions,
     ) -> DurableResult<SpawnResult> {
-        // Validate that the task is registered
-        {
-            let registry = self.registry.read().await;
-            if !registry.contains_key(task_name) {
-                return Err(DurableError::TaskNotRegistered {
-                    task_name: task_name.to_string(),
-                });
-            }
-        }
-
-        self.spawn_by_name_internal(&self.pool, task_name, params, options)
+        self.spawn_by_name_with(&self.pool, task_name, params, options)
             .await
     }
 
@@ -432,11 +422,16 @@ where
         // Validate that the task is registered
         {
             let registry = self.registry.read().await;
-            if !registry.contains_key(task_name) {
+            let Some(task) = registry.get(task_name) else {
                 return Err(DurableError::TaskNotRegistered {
                     task_name: task_name.to_string(),
                 });
-            }
+            };
+            task.validate_params(params.clone())
+                .map_err(|e| DurableError::InvalidTaskParams {
+                    task_name: task_name.to_string(),
+                    message: e.to_string(),
+                })?;
         }
 
         self.spawn_by_name_internal(executor, task_name, params, options)
diff --git a/src/error.rs b/src/error.rs
index f55fcfc..8972ad5 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -311,6 +311,18 @@ pub enum DurableError {
         task_name: String,
     },
 
+    //// Task params validation failed.
+    ///
+    /// Returned when the task definition in the registry fails to validate the params
+    /// (before we attempt to spawn the task in Postgres).
+    #[error("invalid task parameters for '{task_name}': {message}")]
+    InvalidTaskParams {
+        /// The name of the task being spawned
+        task_name: String,
+        /// The error message from the task.
+        message: String,
+    },
+
     /// Header key uses a reserved prefix.
     ///
     /// User-provided headers cannot start with "durable::" as this prefix
diff --git a/src/task.rs b/src/task.rs
index 54f6019..c857c6d 100644
--- a/src/task.rs
+++ b/src/task.rs
@@ -109,6 +109,8 @@ where
     State: Clone + Send + Sync + 'static,
 {
     fn name(&self) -> Cow<'static, str>;
+    /// Called before spawning, to check that the `params` are valid for this task.
+    fn validate_params(&self, params: JsonValue) -> Result<(), TaskError>;
     async fn execute(
         &self,
         params: JsonValue,
@@ -127,6 +129,12 @@ where
         T::name()
     }
 
+    fn validate_params(&self, params: JsonValue) -> Result<(), TaskError> {
+        // For now, just deserialize
+        let _typed_params: T::Params = serde_json::from_value(params)?;
+        Ok(())
+    }
+
     async fn execute(
         &self,
         params: JsonValue,
diff --git a/tests/spawn_test.rs b/tests/spawn_test.rs
index 5a79dd2..247f840 100644
--- a/tests/spawn_test.rs
+++ b/tests/spawn_test.rs
@@ -3,7 +3,7 @@
 mod common;
 
 use common::tasks::{EchoParams, EchoTask, FailingParams, FailingTask};
-use durable::{CancellationPolicy, Durable, MIGRATOR, RetryStrategy, SpawnOptions};
+use durable::{CancellationPolicy, Durable, DurableError, MIGRATOR, RetryStrategy, SpawnOptions};
 use sqlx::PgPool;
 use std::collections::HashMap;
 use std::time::Duration;
@@ -270,6 +270,33 @@ async fn test_spawn_by_name(pool: PgPool) -> sqlx::Result<()> {
     Ok(())
 }
 
+#[sqlx::test(migrator = "MIGRATOR")]
+async fn test_spawn_by_name_invalid_params(pool: PgPool) -> sqlx::Result<()> {
+    let client = create_client(pool.clone(), "spawn_by_name").await;
+    client.create_queue(None).await.unwrap();
+    client.register::<EchoTask>().await.unwrap();
+
+    let params = serde_json::json!({
+        "message": 12345
+    });
+
+    let result = client
+        .spawn_by_name("echo", params, SpawnOptions::default())
+        .await
+        .expect_err("Spawning task by name with invalid params should fail");
+
+    let DurableError::InvalidTaskParams { task_name, message } = result else {
+        panic!("Unexpected error: {}", result);
+    };
+    assert_eq!(task_name, "echo");
+    assert_eq!(
+        message,
+        "serialization error: invalid type: integer `12345`, expected a string"
+    );
+
+    Ok(())
+}
+
 #[sqlx::test(migrator = "MIGRATOR")]
 async fn test_spawn_by_name_with_options(pool: PgPool) -> sqlx::Result<()> {
     let client = create_client(pool.clone(), "spawn_by_name_opts").await;
@@ -308,9 +335,10 @@ async fn test_spawn_with_empty_params(pool: PgPool) -> sqlx::Result<()> {
     client.create_queue(None).await.unwrap();
     client.register::<EchoTask>().await.unwrap();
 
-    // Empty object is valid JSON params for EchoTask (message will be missing but that's ok for this test)
+    // Empty object is not valid JSON params for EchoTask,
+    // but spawn_by_name_unchecked does not validate the JSON
     let result = client
-        .spawn_by_name("echo", serde_json::json!({}), SpawnOptions::default())
+        .spawn_by_name_unchecked("echo", serde_json::json!({}), SpawnOptions::default())
         .await
         .expect("Failed to spawn task with empty params");
 
@@ -326,7 +354,8 @@ async fn test_spawn_with_complex_params(pool: PgPool) -> sqlx::Result<()> {
     client.register::<EchoTask>().await.unwrap();
 
     // Complex nested JSON structure - the params don't need to match the task's Params type
-    // because spawn_by_name accepts arbitrary JSON
+    // because spawn_by_name_unchecked does not validate the JSON
+    // (unlike `spawn_by_name`)
     let params = serde_json::json!({
         "nested": {
             "array": [1, 2, 3],
@@ -341,7 +370,7 @@ async fn test_spawn_with_complex_params(pool: PgPool) -> sqlx::Result<()> {
     });
 
     let result = client
-        .spawn_by_name("echo", params, SpawnOptions::default())
+        .spawn_by_name_unchecked("echo", params, SpawnOptions::default())
         .await
         .expect("Failed to spawn task with complex params");