Fabric Tmdl Api

Semantic Model Definition API rules

• Two audiences: Fabric API (api.fabric.microsoft.com) for CRUD on definitions; Power BI API (analysis.windows.net/powerbi/api) for refresh, data sources, permissions
• updateDefinition must include ALL parts — modified AND unmodified. The API replaces the entire definition; omitting parts deletes them.
• Never include .platform in updateDefinition payloads — it is Git integration metadata and causes errors
• Base64-encode all TMDL content in definition payloads
• getDefinition is a POST (not GET) — requires --body '{}'
• Poll LRO to completion — createItemWithDefinition, getDefinition, and updateDefinition return 202

Required TMDL Parts

| Part Path | Content | |---|---| | definition.pbism | Semantic model connection settings (JSON) | | definition/database.tmdl | database declaration + compatibilityLevel: 1702 | | definition/model.tmdl | Model properties + ref declarations for tables/roles/etc. | | definition/tables/.tmdl | Per-table: measures, columns, partitions |

Critical: database.tmdl MUST start with database object declaration, not bare properties. Bare compatibilityLevel: causes InvalidLineType: Property! errors.

model.tmdl Required Properties

model Model
 culture: en-US
 defaultPowerBIDataSourceVersion: powerBI_V3
 discourageImplicitMeasures

defaultPowerBIDataSourceVersion: powerBI_V3 is required for Import-mode models. Without it: Import from JSON supported for V3 models only.

Direct Lake Configuration

• ALL partitions must use EntityPartitionSource — no M/Power Query
• A named expression pointing to the Lakehouse/Warehouse must be defined before tables:

``tmdl expression DL_Lakehouse = let Source = AzureStorage.DataLake("https://onelake.dfs.fabric.microsoft.com//", [HierarchicalNavigation=true]) in Source ``

• Each table partition references the expression:

``tmdl partition Sales = entity mode: directLake source entityName: Sales schemaName: dbo expressionSource: DL_Lakehouse ``

• dataType: binary columns are NOT supported in Direct Lake
• Columns map directly via sourceColumn — no transforms
• Calculated columns / tables (April 2026 preview): Direct Lake on OneLake now supports unmaterialized calculated columns (and calculated tables that reference them). Direct Lake on SQL still does not. User-context-aware DAX (USERCULTURE, USERPRINCIPALNAME, CUSTOMDATA, etc.) requires expressionContext: userContext on the column. See fabric-tmdl REFERENCE for the storage-mode × Expression-Context support matrix.

Reference

• Microsoft Learn: Item definition overview (Fabric REST)
• Microsoft Learn: SemanticModel definition envelope
• Microsoft Learn: Develop Direct Lake semantic models (TMDL partition mode)
• Comprehensive MS Learn link bundle (definition envelope / REST CRUD / TMDL language / required parts / Direct Lake configuration / refresh APIs): [references/REFERENCE.md](references/REFERENCE.md)

See also

• fabric-rest-api skill — LRO polling pattern, runtime item ID vs logicalId
• fabric-auth skill — Fabric vs Power BI audience selection
• fabric-cli skill — fab export / fab import wrap these APIs

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: wardawgmalvicious
• Source: wardawgmalvicious/claude-config
• License: MIT

Install and usage instructions live in the source repository linked above.