dbt-preflight

Purpose

Inspect a dbt change set before it ships: identify which assets changed, estimate downstream impact, detect likely gaps in testing, contracts, documentation, and YAML alignment, and recommend the narrowest safe validation path. Preflight is read-only — do not edit code unless explicitly asked.

When to Use

• Before opening a PR in an analytics repository
• Reviewing someone else's dbt change
• Assessing the risk of a change whose downstream impact is unclear

Inputs

• The change set (branch diff or working tree)
• The dbt project, for lineage and selector queries

Workflow

1. Enumerate changed assets:

   git diff --name-status origin/main...HEAD

   Classify each change: models, snapshots, seeds, macros, tests, schema YAML, semantic models, metrics, saved queries, exposures or BI-facing assets.

2. Estimate blast radius. For each changed model, list downstream dependents:

   dbt ls --select <model>+

   If a production manifest is available, cover the whole change set at once:

   dbt ls --select state:modified+ --state <path-to-prod-artifacts>

3. Run the review checklist. Check for:
   • model grain changes
   • renamed columns or breaking contract changes
   • missing or weakened tests
   • YAML not updated after model changes
   • metrics or semantic definitions drifting from prior meaning
   • high blast radius due to downstream dependencies
   • incremental logic changes
   • snapshot logic changes
   • joins or filters that may alter business meaning

4. Recommend the narrowest meaningful validation path first:

   1. targeted checks: dbt build --select <changed_model>
   2. narrow downstream checks: dbt build --select <changed_model>+1
   3. broader PR-level validation only if needed: dbt build --select state:modified+ --state <path>

   If exact commands are available in the repo (Makefile, CI config, docs), prefer them. If not, say what should be validated conceptually.

Output

1. changed assets summary
2. likely blast radius
3. likely missing checks or weak spots
4. recommended validation plan
5. items that need stakeholder or domain-owner confirmation

Verification

• Every changed file classified by asset type
• Blast radius backed by lineage (dbt ls), not guessed
• Each checklist hit mapped to a recommended validation step
• Validation plan starts with the narrowest step that covers the risk
• Stakeholder-confirmation items listed separately

Failure Modes

• Style distraction — preflight is about correctness and semantic impact, not formatting.
• Overclaiming impact — be conservative with claims; verify lineage before asserting blast radius.
• Validating everything — defaulting to a full rebuild obscures which check actually covers the risk; the goal is the narrowest safe path.
• Editing instead of reporting — do not edit code unless explicitly asked.