Power BI Validation and Self-Testing

Overview

Validation skill for any TMDL, PBIR, DAX, or M artifact a developer (or Claude) generates. The goal: catch syntax, schema, and best-practice errors locally before a Fabric REST deploy fails. This skill is essential for the powerbi-expert agent's Self-Validation Protocol -- whenever the agent writes TMDL or PBIR, it should describe (or run) the matching validation step from this skill.

As of 2026, Power BI validation has four distinct layers, each catching a different class of error:

The cardinal rule: never deploy without passing layers 1 and 2; never merge to main without passing layer 3.

2026 Validation Tooling Snapshot

Self-Validation Protocol (For Generated Artifacts)

When generating TMDL or PBIR artifacts inside an agent loop, follow this minimum protocol:

1. Before writing files -- mentally validate the structure: every object reference must resolve, every required property must be set.
2. After writing files -- run a syntax-level parse (TmdlSerializer for TMDL; JSON schema validation for PBIR).
3. Before suggesting deployment -- run a BPA pass (Tabular Editor CLI or semantic-link-labs).
4. Report results inline -- never silently swallow validation errors. Surface line numbers, file paths, and the specific rule that failed.

A valid agent response that generates a 50-line TMDL measure block should always be followed by either:

• (a) A validation script the user can paste, OR
• (b) An inline Bash/PowerShell/Python validation invocation if the environment supports it.

TMDL Validation -- Layer 1 (Syntax Parser)

The fastest, lowest-dependency TMDL syntax check is TmdlSerializer.DeserializeDatabaseFromFolder. It throws:

• TmdlFormatException -- the TMDL text has invalid syntax (bad keyword, wrong indentation, malformed expression). Includes Document, Line, and LineText properties pointing to the exact location.
• TmdlSerializationException -- the TMDL text parses but produces invalid TOM metadata (e.g., a column references a dataType that doesn't exist, or a partition references an unknown data source).

Minimal C# validator (.NET 8):

using Microsoft.AnalysisServices.Tabular;
using Microsoft.AnalysisServices.Tabular.Tmdl;

string folder = args[0];
try
{
    var db = TmdlSerializer.DeserializeDatabaseFromFolder(folder);
    Console.WriteLine($"OK: TMDL parsed. CompatLevel={db.CompatibilityLevel}, Tables={db.Model.Tables.Count}");
    return 0;
}
catch (TmdlFormatException fx)
{
    Console.Error.WriteLine($"SYNTAX ERROR  {fx.Document}:{fx.Line}");
    Console.Error.WriteLine($"  {fx.LineText}");
    Console.Error.WriteLine($"  -> {fx.Message}");
    return 1;
}
catch (TmdlSerializationException sx)
{
    Console.Error.WriteLine($"METADATA ERROR  {sx.Document}:{sx.Line}");
    Console.Error.WriteLine($"  {sx.Message}");
    return 2;
}

One-liner via Tabular Editor 2 CLI (no C# project required):

# Loads TMDL folder; non-zero exit on parse failure
TabularEditor.exe "MyProject.SemanticModel/definition" -B "MyProject.bim"

The -B (bim output) switch forces a deserialize + reserialize round-trip. Any parse failure exits non-zero with the error written to stderr.

For full scripted patterns and Python equivalents, see references/tmdl-validation-recipes.md.

TMDL Validation -- Layer 3 (Best Practice Analyzer)

The Best Practice Analyzer (BPA) is the canonical anti-pattern checker for tabular models. It is the same engine in Tabular Editor 2, Tabular Editor 3, semantic-link-labs, and Fabric > Workspace settings > Best Practice Analyzer.

Tabular Editor 2 CLI (free, recommended for CI):

# Run BPA against a TMDL folder using the official Microsoft rule set
TabularEditor.exe "MyProject.SemanticModel/definition" \
  -A "https://raw.githubusercontent.com/TabularEditor/BestPracticeRules/master/BPARules.json" \
  -V \
  -G

# Exit codes:
#   0 = no violations
#   1 = warnings only
#   2 = errors found (any rule with Severity >= 3) -- pipeline should FAIL

Switches that matter for CI/CD:

Severity-driven failure: when a BPA rule is set to Error (level 3), the CLI immediately stops and exits non-zero. Set BPA rules to Error severity for any anti-pattern that should block a PR; set to Warning for advisory-only rules.

Standard Microsoft rule set: TabularEditor/BestPracticeRules -- ~60 rules covering performance, error prevention, DAX, maintenance, and naming. Always pin to a specific commit in CI.

For a complete BPA rule reference (every Microsoft rule explained, plus how to author custom rules), see references/bpa-rules-reference.md.

TMDL Validation from Python (semantic-link-labs)

%pip install semantic-link-labs -q
import sempy_labs as labs

# Run the default BPA against a deployed model
results = labs.run_model_bpa(
    dataset="SalesModel",
    workspace="Sales-Dev",
    extended=True,        # adds VertiPaq Analyzer stats for performance rules
)
results.head(20)

# Run BPA against every model in a workspace and store to delta
labs.run_model_bpa_bulk(
    workspace="Sales-Dev",
    extended=True,
)

# Custom rule set from a JSON file in the lakehouse
my_rules = labs.model_bpa_rules()  # built-in rule definitions
my_rules.append({
    "ID": "AVOID_AUTO_DATE",
    "Name": "Disable auto date/time",
    "Category": "Performance",
    "Severity": 3,
    "Scope": "Model",
    "Expression": "DiscourageImplicitMeasures and not AutoDateTime",
})
labs.run_model_bpa(dataset="SalesModel", rules=my_rules)

semantic-link-labs is the Python path for layer 3. Use it inside Fabric notebooks, scheduled BPA runs, or Spark pipelines. See references/tmdl-validation-recipes.md for the full Python validation cookbook including offline TMDL parse from a local folder.

PBIR Validation -- Layer 1 (JSON Schema)

Every PBIR file embeds a $schema URL pointing to the official Microsoft schema in microsoft/json-schemas. This means any JSON Schema validator can syntax-check PBIR files locally.

Python jsonschema validator:

import json
import urllib.request
from pathlib import Path
from jsonschema import Draft202012Validator, RefResolver

def validate_pbir_file(pbir_file: Path) -> list[str]:
    doc = json.loads(pbir_file.read_text(encoding="utf-8"))
    schema_url = doc.get("$schema")
    if not schema_url:
        return [f"{pbir_file}: no $schema declared"]

    schema = json.loads(urllib.request.urlopen(schema_url).read())
    validator = Draft202012Validator(schema)
    errors = sorted(validator.iter_errors(doc), key=lambda e: e.path)
    return [f"{pbir_file}#{'/'.join(map(str, e.path))}: {e.message}" for e in errors]

# Walk the entire PBIR folder
report_root = Path("MyProject.Report/definition")
all_errors = []
for f in report_root.rglob("*.json"):
    all_errors.extend(validate_pbir_file(f))

if all_errors:
    print(f"FAIL: {len(all_errors)} schema violations")
    for e in all_errors[:50]:
        print(f"  {e}")
    raise SystemExit(1)
print(f"OK: validated {sum(1 for _ in report_root.rglob('*.json'))} PBIR files")

Cache the schemas locally for offline CI: git clone https://github.com/microsoft/json-schemas.git once, then point RefResolver at the local copy. Stops your CI from making 1000+ HTTP calls per build.

PBIR Validation -- Layer 3 (PBI-InspectorV2 / Fab Inspector)

NatVanG/PBI-InspectorV2 (also known as Fab Inspector) is the canonical rules-based PBIR/PBIP validator. v2.3+ supports all Fabric item types (semantic models, reports, notebooks, lakehouses) via the -fabricitem switch and the new PBIR enhanced format (the original PBI-Inspector repo only handles PBIR-Legacy).

Install (cross-platform .NET tool):

# Download the latest release from https://github.com/NatVanG/PBI-InspectorV2/releases
# Or use the published Docker image
docker pull natvang/pbi-inspector-v2:latest

Run against a PBIP folder:

PBIInspectorCLI \
  -fabricitem "./MyProject.Report" \
  -rules "./pbi-inspector-rules.json" \
  -formats "JSON,HTML,GitHub" \
  -output "./inspector-results"

# Exit codes:
#   0 = all rules passed
#   1 = warnings only
#   2 = at least one Error-severity rule failed

Rules format -- start from Base-rules.json and customize. Each rule has:

• Name (display)
• Description
• LogType (Error / Warning / Info)
• Disabled (skip without deleting)
• Path (JSONPath into PBIR file)
• Test (one of isEqualTo, isGreaterThan, isLessThan, mustExist, mustNotExist, regex, etc.)

Common rules to enforce on every PBIR PR:

[
  {
    "Name": "All visuals have a title",
    "LogType": "Error",
    "Path": "$.visual.objects.title[0].properties.show.expr.Literal.Value",
    "Test": "isEqualTo",
    "Expected": "true"
  },
  {
    "Name": "Page count under limit",
    "LogType": "Error",
    "Path": "$.pages",
    "Test": "arrayLengthLessThan",
    "Expected": 1000
  },
  {
    "Name": "Bookmarks reference real pages",
    "LogType": "Error",
    "Path": "$.children[?(@.targetSection)].targetSection",
    "Test": "mustResolveToPage"
  }
]

Full rule examples and CI gating patterns in references/pbir-validation-recipes.md.

Fabric CI/CD, DAX, Lineage, CI Gates & Error Catalog

Focused recipes for fabric-cicd pre-deployment validation, DAX syntax validation without a server, and lineage / cross-reference validation live in references/fabric-dax-lineage-validation.md. GitHub Actions CI gate patterns, common error mappings, and static-validation limits live in references/ci-gates-and-error-catalog.md.

Additional Resources

Reference Files

• references/tmdl-validation-recipes.md -- Full TMDL validation cookbook: TmdlSerializer C# patterns, Python pythonnet wrapper, Tabular Editor C# scripts, INFO DAX introspection, offline parsing
• references/pbir-validation-recipes.md -- PBIR JSON schema validation, PBI-InspectorV2 rule examples, lineage cross-reference linter, GitHub Actions integration
• references/bpa-rules-reference.md -- The standard Microsoft BPA ruleset summary, rule authoring guide, severity strategy, and pinning recipes
• references/fabric-dax-lineage-validation.md -- fabric-cicd, DAX syntax, and lineage validation recipes
• references/ci-gates-and-error-catalog.md -- CI gate patterns, common validation errors, and static-validation limits

Related Skills

• powerbi-master:tmdl-mastery -- TMDL syntax reference (use this when generating TMDL; come back here to validate it)
• powerbi-master:programmatic-development -- PBIR generation (use this when generating PBIR; come back here to validate it)
• powerbi-master:performance-optimization -- For run-time validation via DAX Studio, VertiPaq Analyzer, Performance Analyzer

Official 2026 References

• TmdlSerializer Class (Microsoft Learn)
• TmdlFormatException Class (Microsoft Learn)
• Tabular Editor BPA documentation
• TabularEditor/BestPracticeRules (official Microsoft rule set)
• NatVanG/PBI-InspectorV2 (Fab Inspector)
• semantic-link-labs Best Practice Analyzer
• microsoft/json-schemas (PBIR official JSON schemas)
• fabric-cicd parameterization