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Step 06 of 10 4-6 months for the first slice· advanced

Step 6: Migrate the First Capability (Vertical Slice)

Ship one complete capability through the new stack. Read-only or low-stakes, self-contained, bounded data — exercises the coexistence layer end-to-end.

What you're doing in this step

Pick a small capability (read-only, self-contained, bounded data). Use the rule catalog from Phase 2 as the spec. Build the modern implementation, build behavior parity tests from the extracted rules, deploy via feature flag in shadow mode (new runs but doesn't affect users), run shadow for weeks, then canary to a small % of users.

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 0.5 day

Feature Flag Rollout Strategy for Migrations

Use feature flags to safely route traffic between legacy and new systems during migration with controlled rollout and instant rollback.

View template
Template· Template 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.

Use this when: The slice is regulated and parity must be proven; expand the parity-test framework you built in earlier migrations

View template
Template· Template reference document

COBOL to Java/.NET Translation Checklist

Pattern-by-pattern translation guide for COBOL constructs to modern Java or .NET equivalents — including the patterns that don't translate.

Use this when: Implementation pattern reference while writing the new code

coboljavadotnet
View template
Template· Template 25 min

OpenAPI 3.1 Spec Generator

Generate a complete OpenAPI 3.1 specification from user stories or a feature description, ready for API-first development.

Use this when: Slice exposes a public API; lock the contract first

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

Spec-Driven Builder Skill

Tool-neutral skill that walks developers through PRD → stories → schema → API → tests for any new feature, producing real artifacts at each step. The methodology is identical on every supported tool.

claude-codecopilotcursor
View skill
Skill· Skill 5 min setup

Test Generator Skill

Claude Code skill that picks the right test type (unit/integration/E2E) based on context and applies Evoke's testing patterns automatically.

claude-code
View skill
Skill· Skill 5 min setup

Code Reviewer Skill

Claude Code skill that performs comprehensive code review on PRs and diffs, prioritized by severity with concrete fixes.

claude-code
View skill
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
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

Azure DevOps MCP for Evoke

Pre-configured Azure DevOps MCP server for Claude Code — work items, repos, PRs, and pipelines from chat.

claude-codemcp
View config
MCP config· MCP config 10 min setup

GitHub MCP for Evoke

Pre-configured GitHub MCP server for Claude Code — issues, PRs, code search, and Actions from chat.

claude-codemcp
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
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
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.

  • Slice 1 implementation complete in the new stack
  • Parity tests pass against extracted rules
  • Shadow mode running, comparing output to mainframe
  • Performance meets targets
  • Internal validation passed
  • Canary rollout to a small user set successful
  • Stop conditions clear; rollback procedure tested
Common pitfalls

What goes wrong at this step

  • Big slice 1 — the first slice should be small enough to fail safely
  • Skipping shadow mode — running new in parallel without affecting users catches bugs that tests miss
  • Performance neglect — cloud-native architectures can be slower than COBOL on hot paths if not designed carefully
  • No rollback drill — the first time you flip the flag back is the worst time to discover it doesn't work
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