windmill-labs/windmill · error

Invalid preprocessor_module: only "rawscript" and "script" m

Error message

Invalid preprocessor_module: only "rawscript" and "script" modules are supported

What it means

A preprocessor_module must have a value of type "rawscript" or "script"; the preprocessor runs inline code before the flow body, so other module types (aiagent, flow, scriptloader, etc.) are invalid there. This complements the id check with a type check on the module's value.

Source

Thrown at frontend/src/lib/components/copilot/chat/flow/editableFlowJson.ts:387

		flow.preprocessor_module,
		'preprocessor_module'
	)
	const failureModule = validateOptionalFlowModule(flow.failure_module, 'failure_module')
	const groupModuleIds = new Set(collectAllFlowModuleIdsFromModules(modules))
	const groups = validateFlowGroups(flow.groups, groupModuleIds)
	const notes = validateFlowNotes(flow.notes, groupModuleIds)

	if (preprocessorModule) {
		if (preprocessorModule.id !== SPECIAL_MODULE_IDS.PREPROCESSOR) {
			throw new Error(
				`Invalid preprocessor_module: id must be "${SPECIAL_MODULE_IDS.PREPROCESSOR}"`
			)
		}
		if (
			preprocessorModule.value.type !== 'rawscript' &&
			preprocessorModule.value.type !== 'script'
		) {
			throw new Error(
				'Invalid preprocessor_module: only "rawscript" and "script" modules are supported'
			)
		}
	}
	if (failureModule) {
		if (failureModule.id !== SPECIAL_MODULE_IDS.FAILURE) {
			throw new Error(`Invalid failure_module: id must be "${SPECIAL_MODULE_IDS.FAILURE}"`)
		}
		if (failureModule.value.type !== 'rawscript' && failureModule.value.type !== 'script') {
			throw new Error('Invalid failure_module: only "rawscript" and "script" modules are supported')
		}
	}

	const ids = new Set(collectAllFlowModuleIdsFromModules(modules))
	if (preprocessorModule) {
		if (ids.has(preprocessorModule.id)) {
			throw new Error(`Duplicate module ID found in preprocessor_module: ${preprocessorModule.id}`)
		}

View on GitHub (pinned to e474e8803c)

Solutions

1. Replace the preprocessor_module value with a rawscript or script value (type, content/code, language set).
2. Move non-script module types into the regular modules list instead.
3. Re-run the tool after converting the module.

Example fix

// before
{"preprocessor_module":{"id":"preprocessor","value":{"type":"aiagent",...}}}
// after
{"preprocessor_module":{"id":"preprocessor","value":{"type":"rawscript","language":"python3","content":"..."}}}

const t = flow.preprocessor_module?.value?.type
if (t && t !== 'rawscript' && t !== 'script')
  throw new Error(`preprocessor_module type must be rawscript|script, got ${t}`)

function isScriptValue(v) {
  return v?.type === 'rawscript' || v?.type === 'script'
}

try {
  validateEditableFlowJson(raw)
} catch (e) {
  if (String(e.message).includes('preprocessor_module: only')) {
    // replace the value with a rawscript/script module or move it to modules
  } else throw e
}

When it happens

Trigger: Calling flowTools modules/patches with preprocessor_module set to a module whose value.type is e.g. "aiagent", "flow", or "identity" while the id is correct.

Common situations: An LLM wires an AI agent or subflow as a preprocessor; a regular module is pasted into preprocessor_module without changing its type; template misuse.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• Invalid ${fieldName}: ${error?.message ?? 'unknown error'}
• Invalid preprocessor_module: id must be "${SPECIAL_MODULE_ID
• Invalid failure_module: id must be "${SPECIAL_MODULE_IDS.FAI
• result.substring(__RESULT_ERR_PREFIX.length)
• Invalid migration name '${name}': use only letters, digits,

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/4e626a11ab30dd40. Report an issue: GitHub.