Write Code in n8n Code Nodes

Teaches Claude the correct data access patterns for Code nodes ($input.all(), $input.item in JavaScript; _input, _json in Python), the critical webhook .body gotcha, correct return format, built-in functions (this.helpers for HTTP, DateTime), Python standard library limitations (no external packages), and the Code Tool node's completely different contract (string return, query input, no $input), so Code nodes run first time instead of failing with "No execution data available" or wrong return format errors.

When you ask to write code in a Code node, this skill activates and shows: for JavaScript, use $input.all() for All Items mode and $input.item for Each Item mode; access webhook data via $json.body.field; return format must be [{json: {...}}]; use this.helpers.httpRequest() for HTTP calls (bare $helpers is undefined in task-runner sandbox). For Python, use _input and _json similarly; accept that no external libraries are available (use standard library: json, datetime, re, etc.); return the same format. For Code Tool (the distinct node attached to AI agents), return a string, not [{json}], and use query (JS) / _query (Python) for input. The skill includes 10 production-tested patterns and top error catalogs (10 patterns cover 62%+ of failures).

Code nodes run in a sandboxed VM with per-invocation setup cost (500-1000ms cold start, amortizes on warm runs); a Code node is roughly 3x slower per-item than an expression for the same logic. Python Code nodes have no external library access (requests, pandas, numpy blocked); JavaScript is recommended for 95% of use cases. Code Tool sandbox has no $input, $helpers, $json, $getWorkflowStaticData access. It's a different environment entirely. The $helpers global in task-runner sandbox is undefined; use this.helpers instead.