prefer-type-fest-json-value

Prefers TypeFest JsonObject for serialization-bound string-keyed record contracts.

Targeted pattern scope

This rule targets boundary-layer Record<string, unknown/any> payload aliases that are intended to represent JSON-compatible values.

Payload/context-like contract aliases using Record<string, unknown>/Record<string, any> in JSON boundary folders.

General-purpose records outside configured JSON boundaries are intentionally excluded.

What this rule reports

This rule reports boundary payload aliases that should use JsonObject.

Payload/context-like contract aliases using Record<string, unknown>/Record<string, any> in JSON boundary folders.

Why this rule exists

Serialization boundaries should declare JSON-compatible intent directly so type safety and runtime assumptions stay aligned.

❌ Incorrect

type Payload = Record<string, unknown>;

✅ Correct

type Payload = JsonObject;

Behavior and migration notes

JsonObject models JSON-compatible object payloads with string keys.
Use JsonObject when your boundary contract must stay object-shaped.
Replace open-ended Record<string, unknown>/any boundary contracts with JsonObject when schema intent is serialization.

Additional examples

❌ Incorrect — Additional example

type ConfigSnapshot = Record<string, unknown>;

✅ Correct — Additional example

type ConfigSnapshot = JsonObject;

✅ Correct — Repository-wide usage

type CacheEntry = JsonObject;

ESLint flat config example

import typefest from "eslint-plugin-typefest";

export default [
    {
        plugins: { typefest },
        rules: {
            "typefest/prefer-type-fest-json-value": "error",
        },
    },
];

When not to use it

Disable this rule if boundary contracts intentionally allow non-JSON runtime values.

Package documentation

TypeFest package documentation:

Source file: source/json-value.d.ts

/**
Matches any valid JSON value.

@see `Jsonify` if you need to transform a type to one that is assignable to `JsonValue`.

@category JSON
*/

Rule catalog ID: R046

prefer-type-fest-json-value

Targeted pattern scope

What this rule reports

Why this rule exists

❌ Incorrect

✅ Correct

Behavior and migration notes

Additional examples

❌ Incorrect — Additional example

✅ Correct — Additional example

✅ Correct — Repository-wide usage

ESLint flat config example

When not to use it

Package documentation

Further reading

Adoption resources

Targeted pattern scope​

What this rule reports​

Why this rule exists​

❌ Incorrect​

✅ Correct​

Behavior and migration notes​

Additional examples​

❌ Incorrect — Additional example​

✅ Correct — Additional example​

✅ Correct — Repository-wide usage​

ESLint flat config example​

When not to use it​

Package documentation​

Further reading​

Adoption resources​

Targeted pattern scope

What this rule reports

Why this rule exists

❌ Incorrect

✅ Correct

Behavior and migration notes

Additional examples

❌ Incorrect — Additional example

✅ Correct — Additional example

✅ Correct — Repository-wide usage

ESLint flat config example

When not to use it

Package documentation

Further reading

Adoption resources