Skip the Designer — Editing Logic Apps Data Mapper LML Files Directly

The Azure Logic Apps Data Mapper has a visual designer in VS Code. You drag lines between schemas, drop in functions, and it generates an .lml file (YAML) that compiles to XSLT 3.0. In theory, you never touch the YAML. In practice, the designer has reliability problems that make direct LML editing the better workflow. Why skip the designer? The designer doesn't always persist changes correctly: Changes revert on reopen — save, close, reopen, and the .lml on disk has the old value String literals lose inner quotes — xpath("'kg'") becomes xpath("kg"), changing a literal to an element reference Expressions get corrupted — conditions like xpath("if (...) then 'Y' else 'N'") lose quote characters Function arguments get rewritten — argument order or paths change silently No undo across sessions — you need git diff to catch silent corruption These happen with normal operations, not edge cases. What LML looks like LML is YAML. Here's a complete map: $version: 1 $input: XML $output: XML $source