More screenshots

    Works with the AI Agents you already use

    Claude CodeClaude CodeCursorCursorCodex CLICodex CLIMuseMuseDotsDots+22 more

    n8n Expression & Mapping Debugger

    1

    Diagnose and fix n8n expression errors, JSON mapping failures, and broken item linking.

    $8.99

    Secure checkout via Stripe

    Money-back guarantee

    Converts to your local currency at checkout

    Security scanned
    n8n Expression & Mapping Debugger

    n8n Expression & Mapping Debugger

    Example session with this skill installed

    My n8n Code node runs once for all items and uses:

    return $input.all().map(item => ({
  json: {
    email: item.json.email.toLowerCase()
  }
}));

    Downstream, {{ $("Webhook").item.json.id }} fails because n8n cannot determine the matching item. Keep one output per input and fix the Code node.

    • Read your context and instructions
    • Compiled the n8n expression

    Cause

    The Code node creates new output items without preserving which input item produced each output. This breaks the item lineage required by {{ $("Webhook").item.json.id }}.

    Corrected code

    return $input.all().map((item, index) => ({
  json: {
    email: item.json.email.toLowerCase()
  },
  pairedItem: {
    item: index
  }
}));

    Why it works

    Each output item is explicitly linked to the input item at the same index. This allows downstream .item references to resolve the corresponding upstream Webhook item.

    Verify

    1. Run the Code node with several input items.
    2. Confirm that input and output item counts match.
    3. Preview {{ $("Webhook").item.json.id }} downstream.
    4. Confirm that each output resolves to the ID of its corresponding Webhook item.

    This assumes that every output corresponds to the input item at the same index and that the earlier lineage back to Webhook is still intact.

    Confidence: High.

    Connects securely to your tools. The creator never sees your data.

    About this skill

    Stop guessing why an n8n field is blank, returns undefined, resolves to the wrong item, or produces [object Object].

    n8n Expression & Mapping Debugger is a focused Agent Skill for diagnosing expression and data-mapping failures inside n8n.

    It helps with

    • nested JSON paths and arrays
    • $json and previous-node references
    • .item, .first() and .all()
    • Merge and Aggregate item-linking problems
    • Code-node pairedItem lineage
    • null and undefined values
    • object-to-text mapping errors

    Give it the failing expression, relevant Input/Output JSON, actual result and expected value. It identifies the smallest proven cause and returns a corrected expression or mapping change, explanation and verification steps.

    The Skill is evidence-first: it does not invent JSON paths, node names or item relationships when the available data is insufficient.

    Best for n8n builders, automation freelancers, agencies and operations teams.

    Scope: n8n expressions and data mapping only. It does not troubleshoot credentials, installation, infrastructure or complete workflow architecture.

    How to use

    Skills on Agensi run inside your AI agent. Copy the prompt, paste it into your agent, and it connects to Agensi and installs this skill for you. If a payment is needed, your agent shows it to you first.

    Reviews

    No reviews yet

    Be one of the first to try it. Every listed skill passes our trust checks below.

    Security scanned

    Passed our 8-point scan before listing

    Fresh listing

    Recently published to Agensi

    Money-back guarantee

    Doesn't do what its page promises? You get your money back.

    Trust & safety

    Security scanned

    Verified clean 1 month ago

    • Passed all security checks, Safe to install

    Listed1 month ago

    What's inside

    Frequently Asked Questions