prefer-type-fest-json-object

Require TypeFest JsonObject over equivalent explicit Record<string, JsonValue> aliases.

Targeted pattern scope

This rule targets direct Record<string, JsonValue> aliases used as JSON object contracts.

Record<string, JsonValue>

Broader record aliases and structurally different object constraints are intentionally left unchanged.

What this rule reports

This rule reports Record<string, JsonValue> aliases that should use JsonObject.

Record<string, JsonValue>

Why this rule exists

JsonObject communicates intent directly and avoids repeating verbose JSON object alias patterns.

❌ Incorrect

type Payload = Record<string, JsonValue>;

✅ Correct

type Payload = JsonObject;

Behavior and migration notes

JsonObject is equivalent in intent to Record<string, JsonValue> for JSON object contracts.
Standardize on JsonObject for shared payload/config types to avoid repeating low-level dictionary syntax.
Keep runtime validation separate; this rule only normalizes compile-time type naming.

Additional examples

❌ Incorrect — Additional example

type Payload = Record<string, JsonValue>;

✅ Correct — Additional example

type Payload = JsonObject;

✅ Correct — Repository-wide usage

type EventAttributes = JsonObject;

ESLint flat config example

import typefest from "eslint-plugin-typefest";

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

When not to use it

Disable this rule if a published API requires preserving existing alias names.

Package documentation

TypeFest package documentation:

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

/**
Matches a JSON object.

This type can be useful to enforce some input to be JSON-compatible or as a super-type to be extended from. Don't use this as a direct return type as the user would have to double-cast it: `jsonObject as unknown as CustomResponse`. Instead, you could extend your CustomResponse type from it to ensure your type only uses JSON-compatible types: `interface CustomResponse extends JsonObject { … }`.

@category JSON
*/

Rule catalog ID: R044

prefer-type-fest-json-object

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