Jinja Template Renderer

Frappe developers building custom print formats, email templates, and report layouts in Jinja2 had no way to preview their work without connecting to a real Frappe instance. Testing a template change meant creating real documents in the system, which was slow and cumbersome. Alternatively, developers would write manual JSON mock data files, but keeping them in sync with evolving templates was error-prone and tedious.

Build a standalone renderer that automatically understands what data a Jinja template expects — and generates matching mock data on the fly — so developers can preview and iterate on templates instantly without any backend.

• Built an AST parser that walks the Jinja2 template tree to extract all variable paths, iterable references, and loop variable mappings — using the actual parser, not fragile regex patterns.

• Implemented automatic mock data generation: the parser infers variable types from usage context and generates plausible values (strings, numbers, dates, lists) without manual configuration.

• Created DocMock, a Frappe-aware mock object that simulates Frappe document fields and methods, enabling realistic previews of print formats and report templates.

• Added a live-reload development server with file watching — changes to templates or data files trigger instant browser refresh via injected polling.

• Included French-locale number formatting support and JSON context export for debugging and sharing template data.

Frappe template developers now iterate on print formats and reports with instant visual feedback and zero backend dependencies — the tool understands what data each template needs and generates it automatically.