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polytype

polytype

One Go type. Many typed projections.
Human docsAgent skill

Agent quickstart

Install the skill, then tell your agent what to build

terminal
npx skills add tylergannon/polytype

Start with the task in front of you

Section titled “Start with the task in front of you”

Generate your first schema

Pin the Go tool, register a type, generate, validate, and commit the outputs.

Model missing and null

Choose ordinary fields, Optional[T], or Nullable[T] without guessing.

Enums and interfaces

Teach tool schemas named values and discriminated implementations.

Validate and prevent drift

Validate LLM output and make CI reject stale generated schemas.

Ship a Go ↔ JavaScript transport

Generate strict Go codecs for the devalue wire format SvelteKit speaks.

Build your own projection

Lower any Go types into the shared type grammar and emit a new target.

One grammar, many projections

Section titled “One grammar, many projections”

polytype lowers Go types, statically at go generate time, into one closed type grammar and projects it into whatever the boundary needs:

Projection How
JSON Schema, embedded in Go, for LLM tool calls and structured output go tool polytype (always on)
ValidateJSON methods --validate
Go JSON codecs: membership-checked enums and discriminated sealed unions Inferred from the types; no flag
Structural TypeScript declarations --typescript DIR, or the typescript package
devalue transport: Go runtime port plus generated typed codecs devalue, devalue/codegen packages
Your own backend grammar, typegrammar packages

What every projection guarantees

Section titled “What every projection guarantees”
  • The Go type is the single source of truth; nothing uses runtime reflection.
  • Property order follows Go struct field order, producing deterministic prompts and stable wire layouts.
  • Unknown properties are rejected: additionalProperties: false in schemas, strict decoders elsewhere.
  • Go doc comments become LLM-facing schema descriptions.
  • Ordinary and nullable fields are required; only Optional[T] removes a property from required.
  • Union discriminators and enum values are the same in every projection.
  • A shape that cannot be represented faithfully fails generation with a diagnostic naming the type or field, instead of widening to any.
  • Generated files are safe to commit and verify in CI.

Need exact exported signatures? The generated Go API reference is available, but most integrations should begin with Getting started.