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Non-functional requirements · Changing it safely next year

Maintainability-style app

Illustrative system design for a changing it safely next year app like Maintainability: 4 topics to read, from requirements to deep dives.

Illustrative design, not Maintainability’s actual implementation. Arrowbox is not affiliated with Maintainability’s owner. Disclaimer

Start with Testing Sign in to start readingUpdated 2 Oct 2026

Core

  • A testing strategy for UIBeginner · 27 min read · Sign in to read

    Spend tests where regressions are likely and expensive: many fast unit and component tests, integration tests that render real components against a fake network, a few end-to-end journeys, plus visual and accessibility checks.

  • Typed contracts at the boundariesIntermediate · 33 min read · Sign in to read

    Types help most where code you don't control meets code you do: API responses, storage, URL params, and shared components. Generate types from the API schema and validate untrusted data once, at the edge.

  • Design tokens and themingIntermediate · 37 min read · Sign in to read

    Named design decisions (colours, spacing, type, radius, motion) stored once and consumed everywhere let five teams stay visually consistent and let themes, dark mode and high-contrast modes change by swapping values, not code.

  • Feature flags, rollouts and removing codeIntermediate · 42 min read · Sign in to read

    Ship code dark, turn it on for a slice of users, watch, then widen or roll back without a deploy. And plan the removal: every flag, shim and deprecated component is debt with an owner and a date.