n8n-io/n8n · error · GuardrailError

error?.description || error?.message || 'Unknown error'

Error message

error?.description || error?.message || 'Unknown error'

What it means

This is the fallback message inside GuardrailError thrown by wrapInGuardrailError() in the Guardrails base helper. It catches any rejection from a guardrail check promise and re-throws a GuardrailError whose message is error?.description || error?.message || 'Unknown error' and whose description is error?.description. It normalizes arbitrary thrown values into the GuardrailError shape so stage aggregation can group them.

Source

Thrown at packages/@n8n/nodes-langchain/nodes/Guardrails/helpers/base.ts:18

import {
	type GuardrailResult,
	GuardrailError,
	type GroupedGuardrailResults,
	type StageGuardRails,
} from '../actions/types';

type RunStageGuardrailsOptions = {
	stageGuardrails: StageGuardRails;
	stage: keyof StageGuardRails;
	inputText: string;
	failOnlyOnErrors?: boolean;
};

// eslint-disable-next-line @typescript-eslint/promise-function-async
const wrapInGuardrailError = (guardrailName: string, promise: Promise<GuardrailResult>) => {
	return promise.catch((error) => {
		throw new GuardrailError(
			guardrailName,
			error?.description || error?.message || 'Unknown error',
			error?.description,
		);
	});
};

export async function runStageGuardrails({
	stageGuardrails,
	stage,
	inputText,
	failOnlyOnErrors,
}: RunStageGuardrailsOptions): Promise<GroupedGuardrailResults> {
	const guardrailPromises: Array<Promise<GuardrailResult>> = [];
	for (const guardrail of stageGuardrails[stage]) {
		guardrailPromises.push(
			wrapInGuardrailError(
				guardrail.name,

View on GitHub (pinned to 5ac6606e81)

Solutions

Inspect the GuardrailError.guardrailName to identify which check threw, then debug that guardrail's check function.
Make custom guardrail implementations throw errors with both `message` and `description` so the surfaced text is meaningful.
Ensure guardrail check functions catch their own internal errors and return a structured GuardrailResult instead of throwing when the failure is a normal 'flagged' outcome.
Reproduce the failing input in isolation against the named guardrail to find the triggering value.

Example fix

// before: guardrail throws a bare string
check: (text) => { if (bad(text)) throw 'invalid'; }
// after: throw an Error with description, or return a structured result
check: (text) => { if (bad(text)) throw new Error('invalid input'); }

Defensive patterns

Strategy: try-catch

Type guard

function isGuardrailError(e): e is GuardrailError { return e instanceof GuardrailError; }

Try / catch

try {
  await runStageGuardrails({ ... });
} catch (e) {
  if (e instanceof GuardrailError) {
    // e.guardrailName tells you which check failed
  }
}

Prevention

Make custom guardrail checks return structured GuardrailResult instead of throwing.
Add try/catch inside custom checks to convert internal errors to results.
Always populate both message and description on thrown errors.

When it happens

Trigger: runStageGuardrails() wraps each guardrail.check(inputText) promise with wrapInGuardrailError. If the check function throws, rejects, or yields a non-GuardrailError, the wrapper converts it. Triggers: a guardrail check throwing a plain Error, a string, or undefined; an exception inside a custom guardrail implementation.

Common situations: A custom guardrail whose check function throws a non-standard error; a third-party guardrail raising an Error without a description; an unexpected runtime fault inside a guardrail (null dereference, bad cast).

Related errors

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/ad2a8bca6b3ded79. Report an issue: GitHub.