FlowiseAI/Flowise · error · Error

Invalid JSON format in body. Original error

Error message

Invalid JSON format in body. Original error: ${error.message}. After cleanup attempts: ${secondError.message}. 3rd attempt: ${thirdError.message}. Final attempt: ${fourthError.message}.\n\nCommon fixes:\n${suggestions.join('\n')}\n\nReceived body: ${body.substring(0, 200)}${body.length > 200 ? '...' : ''}

What it means

Thrown after JSON/JSON5 parsing fails four successive attempts (JSON5 original, JSON5 cleaned, JSON.parse original, JSON.parse cleaned). The message aggregates all four error messages plus remediation hints and a 200-char preview of the received body. It indicates the input is structurally not parseable JSON even after common cleanup (trailing commas, single quotes, comments, backslash escapes).

Solutions

Inspect the 200-char preview in the message to see what was actually received (HTML? truncated? wrong format?).
Fix the upstream sender to send well-formed JSON with double quotes, no trailing commas, no comments.
If a proxy injects error pages, ensure requests reach the API route (check Content-Type and routing).
Increase any body-size limits so payloads aren't truncated before parsing.

Example fix

// before — single throw with aggregated message
throw new Error(`Invalid JSON format in body. Original error: ${error.message}. ... Received body: ${body.substring(0,200)}...`)

// caller-side: guard before calling the parser
if (!body || !body.trim().startsWith('{') && !body.trim().startsWith('[')) {
  return res.status(400).json({ error: 'Expected JSON object or array', preview: body.substring(0, 200) })
}

Defensive patterns

Strategy: validation

Validate before calling

function looksLikeJson(body: string): boolean {
  const t = (body || '').trim()
  return t.startsWith('{') || t.startsWith('[')
}

Type guard

function isJsonArrayOrObject(body: string): boolean {
  const t = body.trim()
  if (!t.startsWith('{') && !t.startsWith('[')) return false
  try { JSON.parse(t); return true } catch { return false }
}

Try / catch

if (!looksLikeJson(body)) {
  throw new Error(`Expected JSON object or array. Received (${body.length} chars): ${body.substring(0, 200)}`)
}

Prevention

Reject non-JSON bodies at the route boundary (400) before parsing.
Ensure reverse proxies return JSON error bodies, not HTML, on application/json routes.
Cap request body size to avoid truncated-payload parsing failures.

When it happens

Trigger: Body is HTML (e.g. an error page from a proxy) instead of JSON; body is truncated by a proxy/gateway mid-payload; body uses a non-JSON format (YAML, XML, form-encoded); nested string contains an unescaped control character; surrogate pairs broken by truncation.

Common situations: Reverse proxy returning its own HTML error page with Content-Type application/json; client sending multipart/form-data but the handler expects JSON; load balancer truncating oversized bodies; AI-generated payloads with subtle syntax errors that the cleanup heuristics can't fix.

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

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/70c23073f3d15e42. Report an issue: GitHub.

Appendix: source

Thrown at packages/components/src/utils.ts:1947

                    const finalCleanedBody = body
                        // eslint-disable-next-line
                        .replace(/\\(?=[\[\]{}])/g, '') // Basic escape cleanup
                        .replace(/,(\s*[}\]])/g, '$1') // Remove trailing commas
                        .trim()

                    return JSON.parse(finalCleanedBody)
                } catch (fourthError) {
                    // Provide comprehensive error message with suggestions
                    const suggestions = [
                        '• Ensure all strings are enclosed in double quotes',
                        '• Remove trailing commas',
                        '• Remove comments (// or /* */)',
                        '• Escape special characters properly (\\n for newlines, \\" for quotes)',
                        '• Use double quotes instead of single quotes',
                        '• Remove unnecessary backslashes before brackets [ ] { }'
                    ]

                    throw new Error(
                        `Invalid JSON format in body. Original error: ${error.message}. ` +
                            `After cleanup attempts: ${secondError.message}. 3rd attempt: ${thirdError.message}. Final attempt: ${fourthError.message}.\n\n` +
                            `Common fixes:\n${suggestions.join('\n')}\n\n` +
                            `Received body: ${body.substring(0, 200)}${body.length > 200 ? '...' : ''}`
                    )
                }
            }
        }
    }
}

/**
 * Parse a value against a Zod schema with automatic type conversion for common type mismatches
 * @param schema - The Zod schema to parse against
 * @param arg - The value to parse
 * @param maxDepth - Maximum recursion depth to prevent infinite loops (default: 10)
 * @returns The parsed value
 * @throws Error if parsing fails after attempting type conversions

View on GitHub (pinned to abe4a8601a)