Reified vs zod

This page maps zod's model onto Reified for readers who know "parse, don't validate" from TypeScript.

Reified's schema group is the same idea zod made mainstream: declare the shape once, parse unknown input through it, and get either a typed value or structured, path-aware issues. If you like zod, Reified should feel familiar — the differences come from F# and .NET, not from a different philosophy.

The Same Moves

zod	Reified
z.object({ name: z.string().max(80) })	schema<...> { field _.Name { constrain (maxLength 80) }; construct ctor }
schema.safeParse(input)	Schema.parse schema raw → Result
result.error.issues with paths	SchemaErrors.toList errors and SchemaPath.format issue.Path
z.string().email().brand<'Email'>()	Schema.refine over a private representation and constraint-backed Refinement
z.discriminatedUnion("type", ...)	Schema.union [ UnionCase.fields ... ]
z.infer<typeof schema>	not needed — the schema is declared against your record type directly
zod-to-json-schema	JsonSchema.generate (in Reified.Schema, from the same metadata)

One inversion worth noticing: zod derives the static type from the schema; Reified declares the schema against a type you own. Your domain type stays an ordinary F# record with real members, and the compiler checks constructor/getter alignment field by field.

What Reified Adds Beyond Parsing

• Trusted-path serialization: Json.compile turns the same declaration into a compiled JSON codec on par with System.Text.Json — zod validates on the way in but does not own the way out.
• Redisplay: failed parses keep the structured data, so form fields re-render with the user's values next to their errors without extra state.
• Workflow policies: environment-aware requirements over already-trusted models, applied per workflow.

Runtime Differences That Matter

• No reflection: Reified schemas are explicit declarations compiled into plans; nothing depends on runtime type inspection, so NativeAOT and aggressive trimming work by construction.
• Fable: the schema core, including Reified.Schema.Json, compiles to JavaScript through Fable, so the browser and the server can share one declaration — encode and decode included — the role zod plays across the TypeScript stack.
• Errors are values with rendering: SchemaError is a typed union with a default English renderer (RetainedParseResult.renderErrors) and a one-function mapping into your own error union (RetainedParseResult.mapErrors), rather than a bag of issue objects.

Where zod Fits Better

zod is the right tool in TypeScript-first codebases — Reified is not trying to run there. The comparison matters when an F#/.NET team asks "what is our zod?": the answer is the schema group of Reified, with plain Result for code that never needed a schema at all.