JSON to TypeScript, Zod, Go, Python and JSON Schema

Several samples become one type, with optionals, nulls and unions.

Writing the interface for an API response by hand is the classic job for a generator, but a single JSON document is misleading: a field that is filled in the sample may be missing in another, an integer may be a decimal on the next row, and a null does not say what the type was. That is why this tool accepts several documents (an array, one JSON after another, or a file with one object per line) and merges them into a single model. A field missing from any sample becomes optional (name?: string, omitempty in Go, Option in Rust, NotRequired in TypedDict). A null makes the field nullable (string | null, a pointer in Go, a nullable type with @SerialName in Kotlin). An integer and a decimal in the same field become a decimal. Genuinely different types become a union: string | number in TypeScript, z.union in Zod, anyOf in JSON Schema, an untagged enum in Rust and json.RawMessage in Go. Objects with the same shape share one type (shipping and billing become Shipping), and type names come from the keys, singularized when they are array items (items becomes Item, addresses becomes Address). The text of every value is inspected too: RFC 3339 date-times (2026-03-14T09:30:00Z), plain dates, UUIDs, emails, URLs and IPv4 addresses are tagged with a format, which produces z.uuid() and z.iso.datetime() in Zod, time.Time in Go, DateTimeOffset and Guid in C#, datetime and UUID in Pydantic, and format in JSON Schema. String fields with a few repeated values (at least 8 samples, at most 10 distinct values, each appearing about twice on average) become an enum. Objects whose keys look like data, such as numeric ids, UUIDs or dates, become a dictionary (Record<string, T>, map[string]T) instead of a type with hundreds of fields. Integers above 9007199254740991 (2^53 - 1) are flagged, because JavaScript reads them with lost digits, and mapped to int64, uint64 or json.Number. Keys that are not identifiers (user-name, 2fa, class) get a valid name in the target language plus the annotation that keeps the original key: a json tag in Go, JsonPropertyName in C#, serde rename in Rust, JsonProperty in Java, SerialName in Kotlin, CodingKeys in Swift and an alias in Pydantic. Everything runs in your browser: the JSON, which is often a real production response, never leaves the page.

Paste the JSON, pick a language and check the decisions.

1. Paste the JSON in the left field, open a file (.json, .jsonl, .txt, up to 10 MB) or use one of the examples. To improve the inference, paste more than one document: one after another, or inside an array.
2. Pick the language with the buttons. Turn on Compare side by side to see two targets at once, adjust the root type name and, under Options, naming style, native dates, immutability and per-language details.
3. Open Inference decisions to check what became optional, a union, an enum or a dictionary. Then copy the code or download the file. The copied link stores only the options, never your JSON.

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Sources and references for this tool

These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.

• JSON Schema 2020-12: CoreJSON Schema, Draft 2020-12 specification: $defs, prefixItems and the basis of the generated schema.
• Zod 4: release notesZod, Top-level format validators (z.email, z.iso.datetime) and z.int() limited to safe integers.
• Zod: APIZod, z.uuid, z.ipv4, z.iso.datetime with offset, z.record(key, value) and z.tuple.
• Serde: container attributesSerde, rename_all values and the untagged representation used in the Rust output.
• JsonStringEnumMemberNameAttributeMicrosoft Learn, System.Text.Json attribute (.NET 9 or later) used for C# enums.

Frequently asked questions

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