---
url: 'https://adk.nht.io/api/@nhtio/adk/common/classes/Tokenizable.md'
description: A mutable string with a built-in token counter.
---

# Class: Tokenizable

Defined in: [lib/classes/tokenizable.ts:101](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L101)

A mutable string with a built-in token counter.

## Remarks

The wrapped string can be read via the standard coercion protocol and updated at any time via
[Tokenizable.set](#property-set). Token counts are computed lazily on first access per encoding and
cached until the value changes, avoiding redundant encoder invocations when the same content
is measured multiple times across a pipeline.

Estimation is dispatched by encoding identifier — see [TokenEncoding](../variables/TokenEncoding.md) for the full list
of supported backends and their accuracy characteristics. Unrecognised encodings fall back to
a `ceil(length / 4)` character heuristic.

The class implements the standard JS value-coercion protocol (`toString`, `valueOf`,
`toJSON`, `toLocaleString`, `Symbol.for('nodejs.util.inspect.custom')`) so instances behave
transparently as strings in most contexts.

## Constructors

### Constructor

```ts
new Tokenizable(value: string): Tokenizable;
```

Defined in: [lib/classes/tokenizable.ts:126](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L126)

#### Parameters

| Parameter | Type     | Description                       |
| --------- | -------- | --------------------------------- |
| `value`   | `string` | The initial string value to wrap. |

#### Returns

`Tokenizable`

## Properties

| Property                                              | Modifier | Type                                                                                                                                                                    | Default value               | Description                                                                                                                                                                                                                                           | Defined in                                                                                                            |
| ----------------------------------------------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------- |
|  `estimateTokens` | `public` | (`encoding`: | `"gpt2"` | `"r50k_base"` | `"p50k_base"` | `"p50k_edit"` | `"cl100k_base"` | `"o200k_base"` | `"gemini"` | `"llama2"` | `"claude"`) => `number` | `undefined`                 | -                                                                                                                                                                                                                                                     | [lib/classes/tokenizable.ts:118](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L118) |
|  `set`                       | `public` | (`value`: `string`) => `void`                                                                                                                                           | `undefined`                 | -                                                                                                                                                                                                                                                     | [lib/classes/tokenizable.ts:117](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L117) |
|  `toJSON`                 | `public` | () => `string`                                                                                                                                                          | `undefined`                 | -                                                                                                                                                                                                                                                     | [lib/classes/tokenizable.ts:113](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L113) |
|  `toLocaleString` | `public` | () => `string`                                                                                                                                                          | `undefined`                 | -                                                                                                                                                                                                                                                     | [lib/classes/tokenizable.ts:116](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L116) |
|  `toString`             | `public` | () => `string`                                                                                                                                                          | `undefined`                 | -                                                                                                                                                                                                                                                     | [lib/classes/tokenizable.ts:114](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L114) |
|  `valueOf`               | `public` | () => `string`                                                                                                                                                          | `undefined`                 | -                                                                                                                                                                                                                                                     | [lib/classes/tokenizable.ts:115](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L115) |
|  `schema`                 | `static` | `AlternativesSchema`<`any`>                                                                                                                                           | `stringOrTokenizableSchema` | Validator schema that accepts a plain `string` or a Tokenizable instance. **Remarks** Reusable fragment for any schema that wants to accept either form — for example, `systemPrompt` and each item in `standingInstructions` in `turnContextSchema`. | [lib/classes/tokenizable.ts:111](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L111) |
|  `TokenEncoding`   | `static` | readonly \[`"gpt2"`, `"r50k_base"`, `"p50k_base"`, `"p50k_edit"`, `"cl100k_base"`, `"o200k_base"`, `"gemini"`, `"llama2"`, `"claude"`]                                 | `TokenEncoding`             | -                                                                                                                                                                                                                                                     | [lib/classes/tokenizable.ts:102](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L102) |

## Methods

### estimateTokens()

```ts
static estimateTokens(value: string, encoding:
  | "gpt2"
  | "r50k_base"
  | "p50k_base"
  | "p50k_edit"
  | "cl100k_base"
  | "o200k_base"
  | "gemini"
  | "llama2"
  | "claude"): number;
```

Defined in: [lib/classes/tokenizable.ts:254](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L254)

Convenience overload for one-off token counting without managing a Tokenizable instance.

#### Parameters

| Parameter  | Type                                                                                                                                          | Description                                  |
| ---------- | --------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------- |
| `value`    | `string`                                                                                                                                      | The string to count tokens for.              |
| `encoding` | | `"gpt2"` | `"r50k_base"` | `"p50k_base"` | `"p50k_edit"` | `"cl100k_base"` | `"o200k_base"` | `"gemini"` | `"llama2"` | `"claude"` | The encoding identifier to use for counting. |

#### Returns

`number`

The estimated number of tokens.

#### Remarks

Creates a temporary instance and immediately discards it — no caching benefit. Use the
instance method when you need to count the same value under multiple encodings or when the
value may change over time.

***

### isTokenizable()

```ts
static isTokenizable(value: unknown): value is Tokenizable;
```

Defined in: [lib/classes/tokenizable.ts:269](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/classes/tokenizable.ts#L269)

Returns `true` if `value` is a Tokenizable instance.

#### Parameters

| Parameter | Type      | Description        |
| --------- | --------- | ------------------ |
| `value`   | `unknown` | The value to test. |

#### Returns

`value is Tokenizable`

`true` when `value` is a Tokenizable instance.

#### Remarks

Uses [@nhtio/adk!isInstanceOf](../../guards/functions/isInstanceOf.md) for cross-realm safety — `instanceof` would fail for instances
created in a different module copy or VM context.