Reflecting on deserialization: why you should explicitly decode your JSON

The familiar shortcut

JSON is the lingua franca of the web, and most developers reach for the same shortcut: define a POCO or DTO, hand the string to Newtonsoft.Json or System.Text.Json, and let reflection do the heavy lifting. It has been reported that many teams default to this pattern because it’s fast, low-friction, and “just works” when you control both sides of an API. But when the world throws you a slightly different shape — a missing field, a renamed key, a subtly wrong type — that magic can slow-roll into bugs that are hard to trace.

What’s at stake?

The original piece argues that reflection-based deserialization trades explicitness for convenience. You get terse code and fewer lines, yes. But you also get runtime mapping that depends on property names, hidden coercions, and sometimes silent failures. The emotional heart of the problem? The surprise. A payload that looks fine in logs can still turn into bad domain objects when the mapper guesses wrong. The author recommends keeping DTOs separate from domain models — an old but still-solid rule of separation of concerns — and questions whether reflection should be the default tool in every situation.

Greener pastures: explicit decoders

Enter explicit decoding: write a focused parser that validates and constructs your types deterministically. The article points to functional languages such as Gleam as examples where explicit decoders are idiomatic, allegedly providing clearer error handling and stronger guarantees at parse time. Explicit decoding is more verbose up front, sure, but it forces you to think about edge cases, versioning, and the contract you actually expect. That upfront pain often pays dividends when real-world inputs go off the rails.

The takeaway

You don’t have to abandon reflection for every endpoint. For internal, well-controlled APIs, the convenience of automatic deserialization often outweighs the cost. But when correctness, resilience, or public contracts matter — or when you want fewer surprises in production — explicitly decoding JSON is a small discipline that can save headaches later. Want fewer midnight bug chases? Be explicit.

Sources: hashset.dev, Lobsters