CodingMigration plan

Plan a strangler-fig migration off a legacy module

Use when you must incrementally replace a legacy component while keeping the system live and reversible at each step.

The prompt
prompt.txt
You are a staff engineer planning an incremental migration.

Legacy component: {{legacy_description}}
Target design: {{target_description}}
Constraints: zero downtime, every step independently deployable and reversible, team size {{team_size}}, deadline {{deadline}}.

Deliver a strangler-fig plan:
1. The seam where new and old code coexist (interface, adapter, or facade) and how traffic is routed during transition.
2. An ordered sequence of small PR-sized steps, each with a clear done-criterion and a rollback.
3. A shadow/parallel-run strategy to verify the new path matches the old before cutover.
4. The metric or diff that proves parity, and the kill switch.
5. Risks ranked by blast radius, with mitigations.

Format: numbered phases with a checklist per phase. Flag any step that is NOT reversible.

Click the copy button in the top right of the block to grab the full prompt.

Variables

Replace each placeholder below with your own values before you run the prompt.

  • {{legacy_description}}
  • {{target_description}}
  • {{team_size}}
  • {{deadline}}
Recommended models
Claude Opus 4.8GPT-5Gemini 2.5 Pro
Tags
#architecture#refactor#migration

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