/core

name: core
description: Core package for defining schemas, catalogs, and AI prompt generation for json-render. Use when working with @json-render/core, defining schemas, creating catalogs, or building JSON specs for UI/video generation.

@json-render/core

Core package for schema definition, catalog creation, and spec streaming.

Key Concepts

• **Schema**: Defines the structure of specs and catalogs (use `defineSchema`)
• **Catalog**: Maps component/action names to their definitions (use `defineCatalog`)
• **Spec**: JSON output from AI that conforms to the schema
• **SpecStream**: JSONL streaming format for progressive spec building

Defining a Schema

import { defineSchema } from "@json-render/core";

export const schema = defineSchema((s) => ({
  spec: s.object({
    // Define spec structure
  }),
  catalog: s.object({
    components: s.map({
      props: s.zod(),
      description: s.string(),
    }),
  }),
}), {
  promptTemplate: myPromptTemplate, // Optional custom AI prompt
});

Creating a Catalog

import { defineCatalog } from "@json-render/core";
import { schema } from "./schema";
import { z } from "zod";

export const catalog = defineCatalog(schema, {
  components: {
    Button: {
      props: z.object({
        label: z.string(),
        variant: z.enum(["primary", "secondary"]).nullable(),
      }),
      description: "Clickable button component",
    },
  },
});

Generating AI Prompts

const systemPrompt = catalog.prompt(); // Uses schema's promptTemplate
const systemPrompt = catalog.prompt({ customRules: ["Rule 1", "Rule 2"] });

SpecStream Utilities

For streaming AI responses (JSONL patches):

import { createSpecStreamCompiler } from "@json-render/core";

const compiler = createSpecStreamCompiler<MySpec>();

// Process streaming chunks
const { result, newPatches } = compiler.push(chunk);

// Get final result
const finalSpec = compiler.getResult();

Dynamic Prop Expressions

Any prop value can be a dynamic expression resolved at render time:

• **`{ "$state": "/state/key" }`** - reads a value from the state model (one-way read)
• **`{ "$bindState": "/path" }`** - two-way binding: reads from state and enables write-back. Use on the natural value prop (value, checked, pressed, etc.) of form components.
• **`{ "$bindItem": "field" }`** - two-way binding to a repeat item field. Use inside repeat scopes.
• **`{ "$cond": <condition>, "$then": <value>, "$else": <value> }`** - evaluates a visibility condition and picks a branch
• **`{ "$template": "Hello, ${/user/name}!" }`** - interpolates `${/path}` references with state values
• **`{ "$computed": "fnName", "args": { "key": <expression> } }`** - calls a registered function with resolved args

`$cond` uses the same syntax as visibility conditions (`$state`, `eq`, `neq`, `not`, arrays for AND). `$then` and `$else` can themselves be expressions (recursive).

Components do not use a `statePath` prop for two-way binding. Instead, use `{ "$bindState": "/path" }` on the natural value prop (e.g. `value`, `checked`, `pressed`).

{
  "color": {
    "$cond": { "$state": "/activeTab", "eq": "home" },
    "$then": "#007AFF",
    "$else": "#8E8E93"
  },
  "label": { "$template": "Welcome, ${/user/name}!" },
  "fullName": {
    "$computed": "fullName",
    "args": {
      "first": { "$state": "/form/firstName" },
      "last": { "$state": "/form/lastName" }
    }
  }
}

import { resolvePropValue, resolveElementProps } from "@json-render/core";

const resolved = resolveElementProps(element.props, { stateModel: myState });

State Watchers

Elements can declare a `watch` field (top-level, sibling of type/props/children) to trigger actions when state values change:

{
  "type": "Select",
  "props": { "value": { "$bindState": "/form/country" }, "options": ["US", "Canada"] },
  "watch": {
    "/form/country": { "action": "loadCities", "params": { "country": { "$state": "/form/country" } } }
  },
  "children": []
}

Watchers only fire on value changes, not on initial render.

Validation

Built-in validation functions: `required`, `email`, `url`, `numeric`, `minLength`, `maxLength`, `min`, `max`, `pattern`, `matches`, `equalTo`, `lessThan`, `greaterThan`, `requiredIf`.

Cross-field validation uses `$state` expressions in args:

import { check } from "@json-render/core";

check.required("Field is required");
check.matches("/form/password", "Passwords must match");
check.lessThan("/form/endDate", "Must be before end date");
check.greaterThan("/form/startDate", "Must be after start date");
check.requiredIf("/form/enableNotifications", "Required when enabled");

User Prompt Builder

Build structured user prompts with optional spec refinement and state context:

import { buildUserPrompt } from "@json-render/core";

// Fresh generation
buildUserPrompt({ prompt: "create a todo app" });

// Refinement with edit modes (default: patch-only)
buildUserPrompt({ prompt: "add a toggle", currentSpec: spec, editModes: ["patch", "merge"] });

// With runtime state
buildUserPrompt({ prompt: "show data", state: { todos: [] } });

Available edit modes: `"patch"` (RFC 6902 JSON Patch), `"merge"` (RFC 7396 Merge Patch), `"diff"` (unified diff).

Spec Validation

Validate spec structure and auto-fix common issues:

import { validateSpec, autoFixSpec } from "@json-render/core";

const { valid, issues } = validateSpec(spec);
// issues include: missing_child, invalid_visible (malformed conditions),
// repeat_without_children, repeat_item_outside_scope, repeat_state_mismatch

const { spec: fixed, fixDetails } = autoFixSpec(spec);
// fixDetails entries are { message, lossy }. Lossless fixes relocate
// misplaced fields; lossy fixes prune dangling children references.
// In a repair loop, withhold lossy fixes until retries are exhausted:
const attempt = autoFixSpec(spec, { lossy: