Parsing LLM Responses in DataWeave: 3-Layer Defense Against Markdown Fences

LLMs often wrap JSON outputs with markdown fences, preamble text, or trailing commentary that breaks direct JSON parsing.

The author implemented a 3-layer DataWeave parser: regex fence extraction, try() wrapping of read(), and required-key validation.

The regex /(?s)(?:json)?\s*(\{.*?\})\s*/ extracts fenced JSON but can fail on nested objects, so additional brace-matching may be needed.

After deploying the 3-layer approach, the parser handled 50,000 responses per day at ~2ms each and eliminated daily flow crashes.