Gpt-Tokenizer

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gpt-tokenizer is a Coding & Development tool that provides a fast JavaScript BPE Tokenizer Encoder/Decoder for OpenAI's GPT models. It supports all current OpenAI models and offers features like chat tokenization and cost estimation.

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At a glance

Pricing

Open Source

Free tier

Yes

API

Yes

Skill level

Technical

About

What is gpt-tokenizer?

gpt-tokenizer is a high-performance JavaScript Byte Pair Encoder/Decoder specifically designed for OpenAI's GPT models, including the latest GPT-5, GPT-4o, and older versions like GPT-3.5 and GPT-4. It serves as a port of OpenAI's tiktoken library but includes additional features such as easy chat tokenization, synchronous loading, and generator functions for encoding and decoding. The library also provides a highly performant `isWithinTokenLimit` function to assess token limits without full encoding and built-in cost estimation with comprehensive pricing information for OpenAI models. It is type-safe, written in TypeScript, and works seamlessly across all JavaScript environments, including browsers.

Best used for

Ideal for developers who need to efficiently tokenize text and chat messages for OpenAI's GPT models, check if input is within token limits, and estimate API usage costs. Especially valuable for integrating advanced tokenization capabilities into JavaScript applications and managing OpenAI API consumption.

Common actions

tokenize text

encode chat

decode tokens

estimate API cost

check token limits

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Capabilities

Key features

BPE tokenizer for OpenAI models
Chat tokenization
Token limit assessment
API cost estimation
Synchronous loading
Generator functions

Target Audience

developer

Integrations

Not yet documented

Pricing & Plans

Open Source

Free

FAQs

Which OpenAI models does gpt-tokenizer support?

gpt-tokenizer supports all current OpenAI models, including the latest GPT-5, GPT-4o, o1, o3, o4, GPT-4.1, and older models like GPT-3.5 and GPT-4. It also supports open-weight Harmony models such as gpt-oss-20b and gpt-oss-120b, covering a wide range of encodings.

Can gpt-tokenizer be used in a browser environment?

Yes, gpt-tokenizer is designed to work out-of-the-box in browser environments. It can be installed as an NPM package or included as a UMD module via a script tag, making it versatile for various JavaScript projects.

How does gpt-tokenizer help with API cost management?

gpt-tokenizer includes an `estimateCost` function that provides built-in cost estimation for calculating API usage. It comes with a comprehensive library of OpenAI models and their pricing information, allowing developers to better manage and predict their API expenses.

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Open Source & Models DevOps & Infrastructure No-Code / Low-Code Testing & QA Backend & APIs Prompt Engineering

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