dax

name: daxdescription: 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.

DAX

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

Object references

Write column references as 'Table'[Column]: the table name is always present and always in single quotes. Write measure references as [Measure], never prefixed with a table. This applies everywhere DAX or model metadata names an object: measure, calculated column and calculation item expressions, RLS filters, format string expressions, DAX queries (te query, pbir model -q), and descriptions or annotations that mention an object.

Why: a measure belongs to the model rather than to its home table, so moving it between tables must not change any expression that uses it; a bare [Measure] also tells the reader at a glance that it is a measure and not a column. An unqualified column is ambiguous as soon as two tables share a column name, and quoting every table name keeps one consistent form whether or not the name needs quotes.

Optimization

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 Tabular Editor CLI te query (see the te-cli skill) first; as an alternative, the connect-pbid skill covers FE/SE timing (performance-profiling.md) and intermediate result inspection (evaluateandlog-debugging.md).
• Remote models (Fabric Service / XMLA): Run DAX with the Tabular Editor CLI te query (-s <workspace> -d <model>) against the workspace XMLA endpoint; see the te-cli skill (tabular-editor plugin).
• Power BI Modeling MCP: also available for trace and query if you prefer an MCP tool; reach for it after the options above.

User-defined functions

• references/udf-authoring.md — UDF signatures, the parameter type system, VAL versus EXPR evaluation, type checks, patterns and testing

Related Skills

• 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