Opinion: Runtime Types vs. Validation — A Pragmatist’s Guide for 2026

Opinion: Runtime Types vs. Validation — A Pragmatist’s Guide for 2026

Hook: There’s a recurring debate: "Should we rely on TypeScript types or add runtime validation everywhere?" In 2026, the right approach is contextual. This guide gives rules of thumb and practical decision criteria.

Rule of thumb

Trust but verify: Use TypeScript for developer ergonomics and compile-time guarantees, and apply runtime validation at trust boundaries — external APIs, untrusted clients, and critical financial flows.

Decision criteria

• Source trustworthiness: External public APIs — validate. Internal packages with strict ownership — prefer type-only with compatibility checks.
• Risk level: Anything affecting money, privacy, or safety needs runtime checks.
• Performance sensitivity: For hot paths, prefer lightweight checks and move in-depth validation off the hot path.

“Types are necessary, but not sufficient. Validation is an investment in trust.”

Operational examples

When designing a payment flow, you should validate payloads at the edge and keep rich invariants in background processors. For marketing experiment flags where retention is a concern, coordinate any change through a product-retention playbook: Retention Tactics.

Tooling and audits

Use codegen to minimize duplication between types and validators. For security-sensitive transforms and protocols, borrow audit frameworks used in other domains, such as DeFi safety audits: DeFi Safety Audit Guide.

Cross-disciplinary references

• When image payloads matter for UX or performance, compression decisions affect validation strategies: JPEG Compression.
• For teams archiving release artifacts or web snapshots to meet compliance, check web archiving tooling: Webrecorder Review.
• Community stories help surface pragmatic compromises — this spotlight is instructive: Community Spotlight.

Final verdict

Adopt a hybrid approach: keep types as your team’s primary design tool, but make runtime validation policy explicit at trust boundaries. Measure the customer and technical impacts of any change — and communicate deprecation windows clearly.