TMDL Authoring

Expert guidance for authoring and editing TMDL (Tabular Model Definition Language) files directly in PBIP projects.

This skill is a last resort. Direct TMDL file editing lacks the validation, atomicity, and DAX query capabilities of the Tabular Editor CLI, Power BI MCP server, or the connect-pbid skill (TOM via PowerShell). Use those tools when available. TMDL editing is appropriate when:

• Working with PBIP files in a Git repo without Power BI Desktop open
• No Tabular Editor CLI or MCP server is installed
• Making quick text-level fixes (descriptions, format strings, display folders) where a full tool chain is overkill

Direct TMDL editing does not validate DAX syntax, check referential integrity, or verify that property values are valid. Errors will only surface when the model is next loaded in Power BI Desktop or deployed via XMLA. Use the pbip-validator agent to check TMDL files for syntax issues, indentation errors, and referential integrity before opening in PBI Desktop.

When to Use This Skill

Activate only when the Tabular Editor CLI, Power BI MCP server, or connect-pbid skill are not available, and tasks involve:

• Editing .tmdl files directly (measures, columns, tables, relationships)
• Adding or modifying measure definitions in TMDL
• Adding descriptions to columns, measures, or tables
• Fixing summarizeBy or formatString values
• Understanding TMDL syntax rules (indentation, quoting, property ordering)
• Writing multi-line DAX in TMDL format
• Understanding the difference between /// descriptions and // comments

Critical