dax

name: dax version: 26.24 description: DAX performance optimization for semantic models. Automatically invoke when the user asks to "optimize DAX", "fix slow DAX", "DAX performance", "tune a measure", "debug a measure", "DAX anti-patterns", or mentions slow queries, server timings, or DAX authoring.

Skills and references for writing, debugging, and optimizing DAX in semantic models.

For systematic DAX query performance optimization, read the workflow reference first:

references/dax-performance-optimization.md — Tiered framework (4 tiers), phased workflow, decision guide, and error handling.

Detailed reference files (progressive disclosure — consult as directed by the workflow):

references/engine-internals.md — FE/SE architecture, xmSQL, compression/segments, SE fusion, trace diagnostics
references/dax-patterns.md — Tier 1 DAX patterns (DAX001–DAX021) + Tier 2 query structure (QRY001–QRY004)
references/model-optimization.md — Tier 3 model patterns (MDL001–MDL009) + Tier 4 Direct Lake (DL001–DL002)

Trace capture and performance profiling:

Local models (Power BI Desktop): Use the connect-pbid skill — specifically performance-profiling.md for FE/SE timing and evaluateandlog-debugging.md for intermediate result inspection.
Remote models (Fabric Service / XMLA): Use the powerbi-modeling-mcp VS Code extension for trace and query operations. Install: code --install-extension analysis-services.powerbi-modeling-mcp

semantic-model — Model design, build, and auditing including DAX anti-patterns and best practices
connect-pbid (pbi-desktop plugin) — Trace capture, performance profiling, EVALUATEANDLOG debugging
lineage-analysis — Impact analysis before model changes