NLTK

What it does

NLTK is a Python library for building programs that work with human language data. It takes text as input and produces outputs such as tokens, part-of-speech tags, named entity labels, and parse trees. It gives access to over 50 corpora and lexical resources, including WordNet, along with libraries for classification, tokenization, stemming, tagging, parsing, and semantic reasoning.

People use NLTK by writing Python code, typically in an interactive session or a script. A common pattern is to tokenize a sentence, tag each token with its part of speech, and then identify named entities or display a parse tree. The project pairs these tools with a hands-on book that teaches programming fundamentals alongside computational linguistics, and with API documentation.

NLTK suits linguists, engineers, students, educators, researchers, and industry users who are comfortable with Python. It is available for Windows, macOS, and Linux and is a free, open source, community-driven project. Users should expect to work in code rather than a graphical interface, and should install the separate NLTK data resources before using many of the corpora.

What it can do

• Tokenize text into words and punctuation
• Tag tokens with part-of-speech labels
• Identify named entities in tagged text
• Display parse trees for treebank sentences
• Access over 50 corpora and lexical resources such as WordNet
• Apply classification, stemming, and semantic reasoning libraries

Before you choose

• Usage requires Python programming knowledge; the documentation describes a code-based library rather than a graphical interface.
• Many corpora and lexical resources are installed separately through the NLTK data installer.
• The online book covers NLTK 3 and Python 3; the original Python 2 edition is a separate legacy resource.

Listed under

• Coding
• Computational linguistics
• Education
• Natural language processing
• NLP
• Open source
• Python

Get started

Follow the installation guide, then install the NLTK data resources.

1. Read the Installing NLTK guide and install the library for your platform.
2. Install the NLTK data resources from the Installing NLTK Data page.
3. Import nltk in a Python session and try tokenizing and tagging a sentence.

No paid plans are listed. Any costs depend on your own Python environment and computing resources.

NLTK is free to use. See their pricing page ↗

Sources for this overview

Product pages, documentation, and pricing checked 29 Oct 2026. Each source supports part of the overview; availability and prices can change.

• NLTK :: Natural Language Toolkit ↗www.nltk.org

Company website

nltk.org: product, pricing and policy pages

GitHub

Public code and releases

YC directory mirror

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Human review

Checked by a person

knowledge_base

manual_review

Last checked 29 Oct 2026. Every field keeps its source and date; unknown means we couldn’t confirm it.