How to Fix Unexpected Token Error When Parsing JSON from Claude in n8n

1// Code node: Run Once for Each Item
2// Robust JSON extraction from Claude responses
3// Handles: markdown fences, surrounding text, escaped characters, nested JSON
4
5const rawOutput = $json.text || $json.output || $json.message?.content || '';
6
7function extractJSON(text) {
8  let cleaned = text.trim();
9
10  // Strategy 1: Remove markdown code fences
11  const fencePatterns = [
12    /```json\s*\n?([\s\S]*?)\n?\s*```/,
13    /```\s*\n?([\s\S]*?)\n?\s*```/,
14    /~~~json\s*\n?([\s\S]*?)\n?\s*~~~/,
15    /~~~\s*\n?([\s\S]*?)\n?\s*~~~/
16  ];
17
18  for (const pattern of fencePatterns) {
19    const match = cleaned.match(pattern);
20    if (match) {
21      cleaned = match[1].trim();
22      break;
23    }
24  }
25
26  // Strategy 2: Try direct parse
27  try {
28    return { data: JSON.parse(cleaned), method: 'direct' };
29  } catch (e) {
30    // Continue to next strategy
31  }
32
33  // Strategy 3: Find JSON object boundaries
34  const firstBrace = cleaned.indexOf('{');
35  const lastBrace = cleaned.lastIndexOf('}');
36  if (firstBrace !== -1 && lastBrace > firstBrace) {
37    try {
38      const substr = cleaned.substring(firstBrace, lastBrace + 1);
39      return { data: JSON.parse(substr), method: 'object_extraction' };
40    } catch (e) {
41      // Continue
42    }
43  }
44
45  // Strategy 4: Find JSON array boundaries
46  const firstBracket = cleaned.indexOf('[');
47  const lastBracket = cleaned.lastIndexOf(']');
48  if (firstBracket !== -1 && lastBracket > firstBracket) {
49    try {
50      const substr = cleaned.substring(firstBracket, lastBracket + 1);
51      return { data: JSON.parse(substr), method: 'array_extraction' };
52    } catch (e) {
53      // Continue
54    }
55  }
56
57  // Strategy 5: Fix common escaping issues
58  let fixedText = cleaned
59    .replace(/[\u2018\u2019]/g, "'")  // Smart quotes
60    .replace(/[\u201C\u201D]/g, '"')  // Smart double quotes
61    .replace(/\\n/g, '\\n')           // Already escaped newlines
62    .replace(/(?<!\\)\n/g, '\\n');    // Unescaped newlines in strings
63
64  try {
65    return { data: JSON.parse(fixedText), method: 'character_fix' };
66  } catch (e) {
67    // All strategies failed
68  }
69
70  return null;
71}
72
73const result = extractJSON(rawOutput);
74
75if (result) {
76  return [{
77    json: {
78      data: result.data,
79      extraction_method: result.method,
80      parse_status: 'success'
81    }
82  }];
83}
84
85// Return the raw text if JSON extraction fails
86return [{
87  json: {
88    raw_text: rawOutput,
89    parse_status: 'failed',
90    suggestion: 'Add stricter JSON-only instructions to your system prompt'
91  }
92}];