FlowiseAI/Flowise · error · Error

Invalid JSON in the Custom Document Loader Input Variables:

Error message

Invalid JSON in the Custom Document Loader Input Variables: ${exception}

What it means

CustomDocumentLoader tries to JSON.parse the functionInputVariables input when it is a string. If the string is not valid JSON, the SyntaxError is caught and re-thrown with this prefix. When the input is already an object it is used as-is and never hits the parser.

Source

Thrown at packages/components/nodes/documentloaders/CustomDocumentLoader/CustomDocumentLoader.ts:88

        const functionInputVariablesRaw = nodeData.inputs?.functionInputVariables
        const appDataSource = options.appDataSource as DataSource
        const databaseEntities = options.databaseEntities as IDatabaseEntity

        const variables = await getVars(appDataSource, databaseEntities, nodeData, options)
        const flow = {
            chatflowId: options.chatflowid,
            sessionId: options.sessionId,
            chatId: options.chatId,
            input
        }

        let inputVars: ICommonObject = {}
        if (functionInputVariablesRaw) {
            try {
                inputVars =
                    typeof functionInputVariablesRaw === 'object' ? functionInputVariablesRaw : JSON.parse(functionInputVariablesRaw)
            } catch (exception) {
                throw new Error('Invalid JSON in the Custom Document Loader Input Variables: ' + exception)
            }
        }

        // Some values might be a stringified JSON, parse it
        for (const key in inputVars) {
            let value = inputVars[key]
            if (typeof value === 'string') {
                value = handleEscapeCharacters(value, true)
                if (value.startsWith('{') && value.endsWith('}')) {
                    try {
                        value = JSON.parse(value)
                    } catch (e) {
                        // ignore
                    }
                }
                inputVars[key] = value
            }
        }

View on GitHub (pinned to abe4a8601a)

Solutions

1. Validate the string with JSON.parse in a scratch console before pasting it into the node.
2. Use double quotes around all keys and string values; remove trailing commas.
3. If the value is built from variables, build the object upstream and pass it as an object rather than a JSON string so the parse branch is skipped.

Example fix

// before
inputVars = typeof functionInputVariablesRaw === 'object'
  ? functionInputVariablesRaw
  : JSON.parse(functionInputVariablesRaw)
// after - explicit, helpful error
if (typeof functionInputVariablesRaw === 'object') {
  inputVars = functionInputVariablesRaw
} else {
  try { inputVars = JSON.parse(functionInputVariablesRaw) }
  catch (exception) {
    throw new Error(`Invalid JSON in Custom Document Loader Input Variables: ${exception.message}. Input was: ${functionInputVariablesRaw}`)
  }
}

function parseInputVars(raw: unknown): Record<string, unknown> {
  if (raw == null) return {}
  if (typeof raw === 'object') return raw as Record<string, unknown>
  if (typeof raw === 'string') {
    try { return JSON.parse(raw) }
    catch (e) { throw new Error(`functionInputVariables is not valid JSON: ${(e as Error).message}. Got: ${raw}`) }
  }
  throw new Error(`functionInputVariables must be an object or JSON string, got ${typeof raw}`)
}
// const inputVars = parseInputVars(nodeData.inputs?.functionInputVariables)

function isJsonString(v: unknown): v is string {
  if (typeof v !== 'string') return false
  try { JSON.parse(v); return true } catch { return false }
}

When it happens

Trigger: User typed input variables as a JS-like object literal with unquoted keys (e.g., {foo: 1}); trailing comma; single quotes instead of double quotes; copy-paste introduced smart quotes; templated variable produced a partial JSON fragment.

Common situations: Confusing JSON syntax with JS object literal syntax; passing a comma-separated 'key=value' list instead of JSON; a templated {{variable}} injecting unescaped quotes.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Invalid JSON in the Chat NVIDIA NIM's baseOptions: ${excepti
• Invalid JSON in the ChatOpenAI's BaseOptions: ${exception}
• Invalid JSON in the ChatOpenAI's BaseOptions: ${exception}
• Invalid JSON in the ChatOpenRouter's BaseOptions: ${exceptio
• Invalid JSON in Search Domain Filter: ${exception}

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/8572842c46c0a70b. Report an issue: GitHub.