diff --git a/web/workspace/src/app.css b/web/workspace/src/app.css
index 789b733a..9d9bd050 100644
--- a/web/workspace/src/app.css
+++ b/web/workspace/src/app.css
@@ -1411,3 +1411,38 @@
   background: rgba(255, 255, 255, 0.04);
   padding: 0.75rem;
 }
+
+@layer components {
+    .worker-submit-error {
+        display: grid;
+        gap: var(--space-2);
+    }
+
+    .worker-submit-error p {
+        margin: 0;
+    }
+
+    .worker-error-diagnostics {
+        display: grid;
+        gap: var(--space-1);
+        margin: 0;
+        padding-left: var(--space-4);
+    }
+
+    .worker-error-diagnostics li {
+        color: var(--text-muted);
+    }
+
+    .worker-error-diagnostics li.error {
+        color: var(--danger);
+    }
+
+    .worker-error-diagnostics strong {
+        color: inherit;
+        font-weight: 750;
+    }
+
+    .worker-error-diagnostics span {
+        display: block;
+    }
+}
diff --git a/web/workspace/src/lib/workspace-sidebar/WorkersNavSection.svelte b/web/workspace/src/lib/workspace-sidebar/WorkersNavSection.svelte
index 4a9acbf3..526776d7 100644
--- a/web/workspace/src/lib/workspace-sidebar/WorkersNavSection.svelte
+++ b/web/workspace/src/lib/workspace-sidebar/WorkersNavSection.svelte
@@ -5,6 +5,7 @@
   import type {
     BrowserCreateWorkerResponse,
     BrowserWorkingDirectoryCreateResponse,
+    Diagnostic,
     ListResponse,
     Worker,
     WorkerLaunchOptionsResponse,
@@ -17,6 +18,17 @@
     workspaceId: string;
   };
 
+  type DisplayError = {
+    message: string;
+    diagnostics: Diagnostic[];
+  };
+
+  type ErrorPayload = {
+    error?: { message?: string; code?: string } | string;
+    message?: string;
+    diagnostics?: Diagnostic[];
+  };
+
   let { currentPath = '/', workspaceId }: Props = $props();
 
   function workerApiPath(path: string): string {
@@ -31,7 +43,7 @@
   let optionsError = $state<string | null>(null);
   let showNewWorker = $state(false);
   let submitting = $state(false);
-  let submitError = $state<string | null>(null);
+  let submitError = $state<DisplayError | null>(null);
   let displayName = $state('Coding Worker');
   let runtimeId = $state('');
   let profile = $state('builtin:coder');
@@ -124,7 +136,7 @@
 
   async function createWorkingDirectory() {
     if (!workingDirectoryRepositoryId) {
-      submitError = 'select a repository before creating a working directory';
+      submitError = { message: 'select a repository before creating a working directory', diagnostics: [] };
       return;
     }
     creatingWorkingDirectory = true;
@@ -140,7 +152,8 @@
         }),
       });
       if (!response.ok) {
-        throw new Error(await responseErrorMessage(response, 'working directory create failed'));
+        submitError = await responseDisplayError(response, 'working directory create failed');
+        return;
       }
       const payload = (await response.json()) as BrowserWorkingDirectoryCreateResponse;
       const items = options?.working_directories ?? [];
@@ -149,7 +162,7 @@
         : options;
       workingDirectoryAllocationId = payload.item.allocation_id;
     } catch (err) {
-      submitError = err instanceof Error ? err.message : 'working directory create failed';
+      submitError = exceptionDisplayError(err, 'working directory create failed');
     } finally {
       creatingWorkingDirectory = false;
     }
@@ -157,7 +170,7 @@
 
   async function createWorker() {
     if (!workspaceId) {
-      submitError = 'workspace id is unavailable';
+      submitError = { message: 'workspace id is unavailable', diagnostics: [] };
       return;
     }
 
@@ -179,32 +192,44 @@
         })),
       });
       if (!response.ok) {
-        throw new Error(await responseErrorMessage(response, 'worker create failed'));
+        submitError = await responseDisplayError(response, 'worker create failed');
+        return;
       }
       const payload = (await response.json()) as BrowserCreateWorkerResponse;
       await loadWorkers();
       window.location.href = payload.console_href;
     } catch (err) {
-      submitError = err instanceof Error ? err.message : 'worker create failed';
+      submitError = exceptionDisplayError(err, 'worker create failed');
     } finally {
       submitting = false;
     }
   }
 
-  async function responseErrorMessage(response: Response, fallback: string): Promise<string> {
+  async function responseDisplayError(response: Response, fallback: string): Promise<DisplayError> {
     try {
-      const payload = (await response.json()) as { error?: { message?: string; code?: string } | string; message?: string };
+      const payload = (await response.json()) as ErrorPayload;
+      const diagnostics = Array.isArray(payload.diagnostics) ? payload.diagnostics : [];
       if (typeof payload.error === 'object' && payload.error?.message) {
-        return `${payload.error.code ?? 'request_failed'}: ${payload.error.message}`;
+        return {
+          message: `${payload.error.code ?? 'request_failed'}: ${payload.error.message}`,
+          diagnostics,
+        };
       }
       if (payload.message) {
         const code = typeof payload.error === 'string' ? payload.error : 'request_failed';
-        return `${code}: ${payload.message}`;
+        return { message: `${code}: ${payload.message}`, diagnostics };
       }
     } catch {
       // fall through
     }
-    return `${fallback} (${response.status})`;
+    return { message: `${fallback} (${response.status})`, diagnostics: [] };
+  }
+
+  function exceptionDisplayError(err: unknown, fallback: string): DisplayError {
+    return {
+      message: err instanceof Error ? err.message : fallback,
+      diagnostics: [],
+    };
   }
 </script>
 
@@ -296,7 +321,19 @@
         <p class="section-state error">{optionsError}</p>
       {/if}
       {#if submitError}
-        <p class="section-state error">{submitError}</p>
+        <div class="section-state error worker-submit-error">
+          <p>{submitError.message}</p>
+          {#if submitError.diagnostics.length > 0}
+            <ul class="worker-error-diagnostics">
+              {#each submitError.diagnostics as diagnostic}
+                <li class={diagnostic.severity}>
+                  <strong>{diagnostic.code}</strong>
+                  <span>{diagnostic.message}</span>
+                </li>
+              {/each}
+            </ul>
+          {/if}
+        </div>
       {/if}
       <button type="submit" disabled={submitting || !runtimeId || !profile || !workingDirectoryAllocationId}>
         {submitting ? 'Starting…' : 'Start Coding Worker'}