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Tag type: modifier

TSDoc standardization: extended

This modifier tag is used with a property of a class or interface. It indicates that the property should be documented as being read-only, even if the type signature indicates otherwise.

This modifier is only needed in special situations. Generally API Extractor will use the property's type signature to determine whether it is read-only.

However, suppose that a class property has a setter function that always throws an exception explaining that the property cannot be assigned. In this situation, the @readonly modifier should be added so that the property will be documented as being read-only.

Usage example:

/** @public */
export class Widget {
* Everyday case: API Extractor will document this property as being read-only.
public get x(): number {
return this._x;

* Special case: We need to tell API Extractor to ignore the property setter.
* @readonly
public get title(): string {
return this._title;

public set title(value: string) {
throw new Error('This property is read-only!');