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Step 06 of 8 1-2 weeks· advanced

Step 6: Validate Parity

Verify the target has the same data as the source — beyond just counts. Investigate any drift before cutover.

What you're doing in this step

Run multi-level validation: row counts, aggregate sums, distributions, FK integrity, sample-row diffs, time-windowed reconciliation, and business invariant checks (sums of related tables match).

Recommended prompts

Use one of these to do the work in your IDE

Open the template to read it in full. Click Copy prompt to grab it (with your stack values pre-filled where they apply) — then paste into Claude Code, Cursor, or wherever you build.

Primary recommendation 1-2 days

Behavior Parity Test Suite

Generate tests that lock down current legacy behavior so the new system doesn't accidentally change it during migration.

View template

Template· Template 1-2 days

Data Migration Plan

Plan a safe data migration: schema mapping, ETL strategy, dual-write or one-shot, validation, and cutover with rollback.

Use this when: Use the validation-queries section of your existing plan instead of starting fresh

View template

Recommended skills

Drop these into Claude Code for this phase

Skills auto-trigger on the right kind of request. Install once; they apply to every prompt that fits.

Skill· Skill 5 min setup

Data Validation Skill

Claude Code skill that compares old and new system outputs for parity — running validation queries on both DBs and reporting drift.

claude-codesql

View skill

Skill· Skill 5 min setup

Database Migration Skill

Claude Code skill that generates safe forward and reverse migrations with transaction-wrapping, idempotency, and zero-downtime patterns.

claude-code

View skill

Recommended MCP configs

Wire these tools into Claude Code first

MCP servers give Claude Code direct access to external systems (Jira, browsers, databases). Configure once.

MCP config· MCP config 10 min setup

Postgres MCP for Evoke

Pre-configured Postgres MCP server for Claude Code — schema inspection and read-only queries to make database work safer and faster.

claude-codemcppostgres

View config

MCP config· MCP config 5 min setup

Filesystem MCP for Evoke

Pre-configured filesystem MCP server for Claude Code — safe, scoped read/write access to project files.

claude-codemcp

View config

When you're done

Verify these in your own work before moving on

This is a checklist for you to mentally tick off in your repo and IDE — the site doesn't track it, you do.

All Level 1-7 validations passed (counts, sums, distributions, FK integrity, spot checks, time-windowed reconciliation, business invariants)
Drift report shows zero unexplained differences
Validation can be re-run on demand
Performance comparison done (top 20 queries on both engines)

Common pitfalls

What goes wrong at this step

Validating only counts — counts can match while individual rows are corrupted
Skipping the spot-check — sample rows reveal field-level translation bugs
Accepting "small" drift — 5 missing rows out of 9M might be 5 missing customer orders
No business invariant checks — sums of related tables (e.g., line items vs order totals) catch issues other checks miss

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