Error 13: Type mismatch in VB.NET Variant assignment

Error 13: Type mismatch in VB.NET Variant assignment

The goal is to establish a repeatable Visual Basic development environment that reliably surfaces type safety issues. In VB.NET projects, the runtime error Error 13: Type mismatch occurs when a Variant or Object containing a non‑numeric string is assigned to a numeric variable or used in an arithmetic expression without an explicit conversion. This behavior is governed by the project’s Option Strict setting.

When Option Strict Off (the legacy default), the compiler accepts the code, but the error surfaces only at runtime, making builds non‑deterministic. Switching to Option Strict On forces the compiler to reject such assignments, providing compile‑time safety but potentially breaking existing code.

Because the language specification does not mandate a default Option Strict value, teams often face an unresolved decision: should the default be On for new projects, or remain Off to preserve legacy behavior? This choice directly impacts build repeatability and error visibility.

• Should the default Option Strict setting be changed to On for new Visual Basic projects?
• What tooling can automatically detect implicit conversions that would trigger Error 13 under Option Strict Off?
• How can a project transition from Off to On without introducing runtime failures?