Script snapshot creation was not successful: ${req.status} -

Error message

Script snapshot creation was not successful: ${req.status} - ${req.statusText} - ${await req.text()}

What it means

In the dev/test panel (Dev.svelte `testBundle`), the built bundle is uploaded to create a script snapshot via a raw fetch. Any non-201 response (auth failure, payload too large, server error, backend down) triggers this error containing status, statusText and the response body.

Source

Thrown at frontend/src/lib/components/Dev.svelte:397

						}
						let blob = new Blob([new Uint8Array(array)], { type: 'application/octet-stream' })

						form.append('file', blob)
					} else {
						form.append('file', file)
					}

					const url = '/api/w/' + workspace + '/jobs/run/preview_bundle'

					const req = await fetch(url, {
						method: 'POST',
						body: form,
						headers: {
							Authorization: 'Bearer ' + token
						}
					})
					if (req.status != 201) {
						throw Error(
							`Script snapshot creation was not successful: ${req.status} - ${
								req.statusText
							} - ${await req.text()}`
						)
					}
					return await req.text()
				} catch (e) {
					sendUserToast(`Failed to send bundle ${e}`, true)
					throw Error(e)
				}
			},
			{
				done(x) {
					loadPastTests()
				}
			}
		)
		loadingCodebaseButton = false

View on GitHub (pinned to e474e8803c)

Solutions

Read the status and body in the error: 401 → re-login; 413 → reduce bundle size; 502 → fix backend port/REMOTE
Re-login to refresh the Bearer token used in the request
Verify the backend is running and the frontend REMOTE points to it
Check the script path/workspace are valid and saved before running a test

Example fix

// diagnose the embedded status
} catch (e) {
  const m = String(e).match(/not successful: (\d+)/);
  if (m?.[1] === '401') await relogin();
  throw e;
}

Defensive patterns

Strategy: retry

Validate before calling

// pre-flight auth + connectivity check
const probe = await fetch(`${backendUrl}/api/workspaces/list`, { headers: { Authorization: `Bearer ${token}` } });
if (probe.status === 401) throw new Error('Session expired — re-login before running tests');

Try / catch

try {
  await runTest();
} catch (e) {
  const status = Number(String(e).match(/not successful: (\d+)/)?.[1]);
  if (status === 401) await reloginAndRetry();
  else if (status >= 500 || status === 0) await retryWithBackoff(runTest);
  else throw e;
}

Prevention

Re-login when dev sessions run long (token expiry)
Keep the frontend REMOTE aligned with the live backend port
Keep test bundles small to avoid 413s
Save the script and confirm the workspace before running tests

When it happens

Trigger: The POST that creates a script snapshot for running a test returns a status other than 201 — e.g. 401 with an expired token, 422 from backend validation, 413 oversized bundle, or 502 because the frontend proxy points at a dead backend.

Common situations: Session token expired during a long dev session, running the frontend with a REMOTE mismatch, backend rebuilt without the workspace/script existing yet, or a syntax/size problem in the generated bundle.

Understand the failure class

Background: 'Something went wrong' / 'Request failed (500)' / 'HTTP error! status: 404' — what failed HTTP requests actually mean and how to find the real cause — this error's family across 28 libraries.

Related errors

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/914d7be9cf22e4dc. Report an issue: GitHub.