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    Code Migration Planner

    1

    The Code Migration Planner is a specialized architect-level skill designed to de-risk complex codebase transitions.

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    Code Migration Planner

    Code Migration Planner

    Example session with this skill installed

    We need to move order management out of our 9-year-old Rails 5 monolith into a new Go service with its own Postgres database. Orders are written by checkout, admin and a nightly ERP sync, and we cannot take downtime.

    • Read your context and instructions
    • Compiled the code migration planner

    Phased plan to move order management from the Rails monolith to the Go service with zero downtime, using strangler-fig routing and gated dual writes.

    Strangler-fig boundary

    • Seam: an OrdersGateway interface inside Rails. All three writers (checkout, admin, ERP sync) must call it before Phase 1 starts.

    Phases

    PhaseWhat changesFlagRollback gate
    0 SeamAll order access via OrdersGatewaynoneTests green, no direct Order calls outside it
    1 Shadow writeRails writes, plus async write to Goorders.shadow_writeNightly diff clean for 7 days
    2 Dual writeSync write to both, Rails is source of truthorders.dual_writeGo write errors under threshold, reconcile clean
    3 Read switchAdmin reads from Go, then checkoutorders.read_from_goSampled response diffs clean
    4 Go primaryGo is source of truth, back-writes to Railsorders.go_primaryReverse flag tested in staging
    5 DecommissionRemove Rails order tables after a retention windownoneFinal export archived

    Rules

    • Only one flag changes per deploy.
    • ERP sync moves last, since it writes in bulk.
    • Every phase has a written rollback drill before it goes to production.

    Next steps

    • Inventory every code path that touches Order to finish Phase 0.
    • Build the diff and reconcile job before enabling shadow writes.

    Connects securely to your tools. The creator never sees your data.

    What you get

    Design zero-downtime database schema migrations using dual-write patternsPlan incremental transitions from legacy frameworks to modern stacksApply the Strangler Fig pattern to decommission monoliths safelyEstablish rollback gates and verification criteria for major version upgrades

    About this skill

    What it does

    The Code Migration Planner is a specialized architect-level skill designed to de-risk complex codebase transitions. It moves beyond simple refactoring by generating staged, incremental migration plans that eliminate "big-bang" deployments. Whether you are moving from Python 2 to 3, transitioning a monolith to microservices, or porting a legacy JS app to TypeScript, this skill structures the move using industry-standard patterns like the Strangler Fig and Dual-Writing.

    Why use this skill

    Typical AI prompts often suggest "replacing X with Y," which leads to long-lived feature branches and integration nightmares. This skill enforces a "shippable main" philosophy. It identifies the riskiest assumptions first and mandates rollback gates for every phase. By using this skill, you ensure that your migration is reversible, verifiable, and continuously integrated into your production environment.

    Key Features

    • Risk-First Sequencing: Prioritizes the most volatile components to prove feasibility early.
    • Strangler Fig Design: Defines clear boundaries to migrate functionality bit-by-bit.
    • Verification Phases: Implements dual-write and comparison logic to ensure data integrity.
    • Feature Flag Routing: Uses flags to manage traffic between old and new implementations.
    • Operational Safety: Defines explicit rollback criteria and "shippable main" constraints for every PR.

    How to install

    Works the same in every agent - Claude, Cursor, Codex, Copilot and 20+ more.

    ~30 seconds
    1. 1

      Download the ZIP

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    2. 2

      Unzip into your skills folder

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    3. 3

      Ask your agent to use it

      Restart the agent if it was already running. It picks the skill up automatically - no config needed.

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    Listed3 months ago
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