FlatType.jsFlatten API JSON. Get typed models.

Compact key-value text that is about half the size of JSON on list payloads, cheaper in LLM prompts, and maps straight to typed models in every frontend framework.

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About half the size on lists

Arrays of same-shaped objects become tables: keys written once, nested fields flattened into the header. 45% smaller than minified JSON on a list of 1,000 users.

Benchmarks

Typed models

defineModel maps snake_case keys, numeric strings and ISO dates for you and reports every problem with its path. Generate models from a sample or an OpenAPI spec.

Models

Every framework

Hooks for React, composables for Vue, signals for Angular, stores for Svelte, resources for Solid, plus fetch, axios and server middleware. Python backends use the same format: pip install flattype.

Frameworks

Built for Claude and LLMs

toPrompt, a tolerant fromModelOutput, real token counts with Claude's tokenizer, and compact MCP / Claude tool results.

LLM helpers

Lossless and safe

decode(encode(x)) equals JSON.parse(JSON.stringify(x)), checked by property-based fuzzing; the decoder is prototype-safe and linear-time.

Security

Small

The core is 6.2 KB min+gz with no third-party dependencies. Every package ships ESM, CJS and types, with npm provenance.

Packages

import { encode } from "@flattype/core";

encode({ page: 1, users: [{ id: 1, name: "Alice", address: { city: "Paris" } }, { id: 2, name: "Bob", address: { city: "Delhi" } }] });
// page: 1
// users[2]{id,name,address.city}:
//   1, Alice, Paris
//   2, Bob, Delhi