---
title: 'spaCy 101: Everything you need to know'
teaser: The most important concepts, explained in simple terms
menu:
- ["What's spaCy?", 'whats-spacy']
- ['Features', 'features']
- ['Linguistic Annotations', 'annotations']
- ['Pipelines', 'pipelines']
- ['Architecture', 'architecture']
- ['Vocab', 'vocab']
- ['Serialization', 'serialization']
- ['Training', 'training']
- ['Language Data', 'language-data']
- ['Community & FAQ', 'community-faq']
---
Whether you're new to spaCy, or just want to brush up on some NLP basics and
implementation details – this page should have you covered. Each section will
explain one of spaCy's features in simple terms and with examples or
illustrations. Some sections will also reappear across the usage guides as a
quick introduction.
> #### Help us improve the docs
>
> Did you spot a mistake or come across explanations that are unclear? We always
> appreciate improvement
> [suggestions](https://github.com/explosion/spaCy/issues) or
> [pull requests](https://github.com/explosion/spaCy/pulls). You can find a
> "Suggest edits" link at the bottom of each page that points you to the source.
[](https://course.spacy.io)
In this course you'll learn how to use spaCy to build advanced natural language
understanding systems, using both rule-based and machine learning approaches. It
includes 55 exercises featuring interactive coding practice, multiple-choice
questions and slide decks.
## What's spaCy? {#whats-spacy}
spaCy is a **free, open-source library** for advanced **Natural Language
Processing** (NLP) in Python.
If you're working with a lot of text, you'll eventually want to know more about
it. For example, what's it about? What do the words mean in context? Who is
doing what to whom? What companies and products are mentioned? Which texts are
similar to each other?
spaCy is designed specifically for **production use** and helps you build
applications that process and "understand" large volumes of text. It can be used
to build **information extraction** or **natural language understanding**
systems, or to pre-process text for **deep learning**.
- [Features](#features)
- [Linguistic annotations](#annotations)
- [Tokenization](#annotations-token)
- [POS tags and dependencies](#annotations-pos-deps)
- [Named entities](#annotations-ner)
- [Word vectors and similarity](#vectors-similarity)
- [Pipelines](#pipelines)
- [Library architecture](#architecture)
- [Vocab, hashes and lexemes](#vocab)
- [Serialization](#serialization)
- [Training](#training)
- [Language data](#language-data)
- [Community & FAQ](#community)
### What spaCy isn't {#what-spacy-isnt}
- **spaCy is not a platform or "an API"**. Unlike a platform, spaCy does not
provide a software as a service, or a web application. It's an open-source
library designed to help you build NLP applications, not a consumable service.
- **spaCy is not an out-of-the-box chat bot engine**. While spaCy can be used to
power conversational applications, it's not designed specifically for chat
bots, and only provides the underlying text processing capabilities.
- **spaCy is not research software**. It's built on the latest research, but
it's designed to get things done. This leads to fairly different design
decisions than [NLTK](https://github.com/nltk/nltk) or
[CoreNLP](https://stanfordnlp.github.io/CoreNLP/), which were created as
platforms for teaching and research. The main difference is that spaCy is
integrated and opinionated. spaCy tries to avoid asking the user to choose
between multiple algorithms that deliver equivalent functionality. Keeping the
menu small lets spaCy deliver generally better performance and developer
experience.
- **spaCy is not a company**. It's an open-source library. Our company
publishing spaCy and other software is called
[Explosion](https://explosion.ai).
## Features {#features}
In the documentation, you'll come across mentions of spaCy's features and
capabilities. Some of them refer to linguistic concepts, while others are
related to more general machine learning functionality.
| Name | Description |
| ------------------------------------- | ------------------------------------------------------------------------------------------------------------------ |
| **Tokenization** | Segmenting text into words, punctuations marks etc. |
| **Part-of-speech** (POS) **Tagging** | Assigning word types to tokens, like verb or noun. |
| **Dependency Parsing** | Assigning syntactic dependency labels, describing the relations between individual tokens, like subject or object. |
| **Lemmatization** | Assigning the base forms of words. For example, the lemma of "was" is "be", and the lemma of "rats" is "rat". |
| **Sentence Boundary Detection** (SBD) | Finding and segmenting individual sentences. |
| **Named Entity Recognition** (NER) | Labelling named "real-world" objects, like persons, companies or locations. |
| **Entity Linking** (EL) | Disambiguating textual entities to unique identifiers in a knowledge base. |
| **Similarity** | Comparing words, text spans and documents and how similar they are to each other. |
| **Text Classification** | Assigning categories or labels to a whole document, or parts of a document. |
| **Rule-based Matching** | Finding sequences of tokens based on their texts and linguistic annotations, similar to regular expressions. |
| **Training** | Updating and improving a statistical model's predictions. |
| **Serialization** | Saving objects to files or byte strings. |
### Statistical models {#statistical-models}
While some of spaCy's features work independently, others require
[trained pipelines](/models) to be loaded, which enable spaCy to **predict**
linguistic annotations – for example, whether a word is a verb or a noun. A
trained pipeline can consist of multiple components that use a statistical model
trained on labeled data. spaCy currently offers trained pipelines for a variety
of languages, which can be installed as individual Python modules. Pipeline
packages can differ in size, speed, memory usage, accuracy and the data they
include. The package you choose always depends on your use case and the texts
you're working with. For a general-purpose use case, the small, default packages
are always a good start. They typically include the following components:
- **Binary weights** for the part-of-speech tagger, dependency parser and named
entity recognizer to predict those annotations in context.
- **Lexical entries** in the vocabulary, i.e. words and their
context-independent attributes like the shape or spelling.
- **Data files** like lemmatization rules and lookup tables.
- **Word vectors**, i.e. multi-dimensional meaning representations of words that
let you determine how similar they are to each other.
- **Configuration** options, like the language and processing pipeline settings
and model implementations to use, to put spaCy in the correct state when you
load the pipeline.
## Linguistic annotations {#annotations}
spaCy provides a variety of linguistic annotations to give you **insights into a
text's grammatical structure**. This includes the word types, like the parts of
speech, and how the words are related to each other. For example, if you're
analyzing text, it makes a huge difference whether a noun is the subject of a
sentence, or the object – or whether "google" is used as a verb, or refers to
the website or company in a specific context.
> #### Loading pipelines
>
> ```cli
> $ python -m spacy download en_core_web_sm
>
> >>> import spacy
> >>> nlp = spacy.load("en_core_web_sm")
> ```
Once you've [downloaded and installed](/usage/models) a trained pipeline, you
can load it via [`spacy.load`](/api/top-level#spacy.load). This will return a
`Language` object containing all components and data needed to process text. We
usually call it `nlp`. Calling the `nlp` object on a string of text will return
a processed `Doc`:
```python
### {executable="true"}
import spacy
nlp = spacy.load("en_core_web_sm")
doc = nlp("Apple is looking at buying U.K. startup for $1 billion")
for token in doc:
print(token.text, token.pos_, token.dep_)
```
Even though a `Doc` is processed – e.g. split into individual words and
annotated – it still holds **all information of the original text**, like
whitespace characters. You can always get the offset of a token into the
original string, or reconstruct the original by joining the tokens and their
trailing whitespace. This way, you'll never lose any information when processing
text with spaCy.
### Tokenization {#annotations-token}
import Tokenization101 from 'usage/101/\_tokenization.md'
To learn more about how spaCy's tokenization rules work in detail, how to
**customize and replace** the default tokenizer and how to **add
language-specific data**, see the usage guides on
[adding languages](/usage/adding-languages) and
[customizing the tokenizer](/usage/linguistic-features#tokenization).
### Part-of-speech tags and dependencies {#annotations-pos-deps model="parser"}
import PosDeps101 from 'usage/101/\_pos-deps.md'
To learn more about **part-of-speech tagging** and rule-based morphology, and
how to **navigate and use the parse tree** effectively, see the usage guides on
[part-of-speech tagging](/usage/linguistic-features#pos-tagging) and
[using the dependency parse](/usage/linguistic-features#dependency-parse).
### Named Entities {#annotations-ner model="ner"}
import NER101 from 'usage/101/\_named-entities.md'
To learn more about entity recognition in spaCy, how to **add your own
entities** to a document and how to **train and update** the entity predictions
of a model, see the usage guides on
[named entity recognition](/usage/linguistic-features#named-entities) and
[training pipelines](/usage/training).
### Word vectors and similarity {#vectors-similarity model="vectors"}
import Vectors101 from 'usage/101/\_vectors-similarity.md'
To learn more about word vectors, how to **customize them** and how to load
**your own vectors** into spaCy, see the usage guide on
[using word vectors and semantic similarities](/usage/linguistic-features#vectors-similarity).
## Pipelines {#pipelines}
import Pipelines101 from 'usage/101/\_pipelines.md'
To learn more about **how processing pipelines work** in detail, how to enable
and disable their components, and how to **create your own**, see the usage
guide on [language processing pipelines](/usage/processing-pipelines).
## Architecture {#architecture}
import Architecture101 from 'usage/101/\_architecture.md'
## Vocab, hashes and lexemes {#vocab}
Whenever possible, spaCy tries to store data in a vocabulary, the
[`Vocab`](/api/vocab), that will be **shared by multiple documents**. To save
memory, spaCy also encodes all strings to **hash values** – in this case for
example, "coffee" has the hash `3197928453018144401`. Entity labels like "ORG"
and part-of-speech tags like "VERB" are also encoded. Internally, spaCy only
"speaks" in hash values.
> - **Token**: A word, punctuation mark etc. _in context_, including its
> attributes, tags and dependencies.
> - **Lexeme**: A "word type" with no context. Includes the word shape and
> flags, e.g. if it's lowercase, a digit or punctuation.
> - **Doc**: A processed container of tokens in context.
> - **Vocab**: The collection of lexemes.
> - **StringStore**: The dictionary mapping hash values to strings, for example
> `3197928453018144401` → "coffee".
If you process lots of documents containing the word "coffee" in all kinds of
different contexts, storing the exact string "coffee" every time would take up
way too much space. So instead, spaCy hashes the string and stores it in the
[`StringStore`](/api/stringstore). You can think of the `StringStore` as a
**lookup table that works in both directions** – you can look up a string to get
its hash, or a hash to get its string:
```python
### {executable="true"}
import spacy
nlp = spacy.load("en_core_web_sm")
doc = nlp("I love coffee")
print(doc.vocab.strings["coffee"]) # 3197928453018144401
print(doc.vocab.strings[3197928453018144401]) # 'coffee'
```
Now that all strings are encoded, the entries in the vocabulary **don't need to
include the word text** themselves. Instead, they can look it up in the
`StringStore` via its hash value. Each entry in the vocabulary, also called
[`Lexeme`](/api/lexeme), contains the **context-independent** information about
a word. For example, no matter if "love" is used as a verb or a noun in some
context, its spelling and whether it consists of alphabetic characters won't
ever change. Its hash value will also always be the same.
```python
### {executable="true"}
import spacy
nlp = spacy.load("en_core_web_sm")
doc = nlp("I love coffee")
for word in doc:
lexeme = doc.vocab[word.text]
print(lexeme.text, lexeme.orth, lexeme.shape_, lexeme.prefix_, lexeme.suffix_,
lexeme.is_alpha, lexeme.is_digit, lexeme.is_title, lexeme.lang_)
```
> - **Text**: The original text of the lexeme.
> - **Orth**: The hash value of the lexeme.
> - **Shape**: The abstract word shape of the lexeme.
> - **Prefix**: By default, the first letter of the word string.
> - **Suffix**: By default, the last three letters of the word string.
> - **is alpha**: Does the lexeme consist of alphabetic characters?
> - **is digit**: Does the lexeme consist of digits?
| Text | Orth | Shape | Prefix | Suffix | is_alpha | is_digit |
| ------ | --------------------- | ------ | ------ | ------ | -------- | -------- |
| I | `4690420944186131903` | `X` | I | I | `True` | `False` |
| love | `3702023516439754181` | `xxxx` | l | ove | `True` | `False` |
| coffee | `3197928453018144401` | `xxxx` | c | fee | `True` | `False` |
The mapping of words to hashes doesn't depend on any state. To make sure each
value is unique, spaCy uses a
[hash function](https://en.wikipedia.org/wiki/Hash_function) to calculate the
hash **based on the word string**. This also means that the hash for "coffee"
will always be the same, no matter which pipeline you're using or how you've
configured spaCy.
However, hashes **cannot be reversed** and there's no way to resolve
`3197928453018144401` back to "coffee". All spaCy can do is look it up in the
vocabulary. That's why you always need to make sure all objects you create have
access to the same vocabulary. If they don't, spaCy might not be able to find
the strings it needs.
```python
### {executable="true"}
import spacy
from spacy.tokens import Doc
from spacy.vocab import Vocab
nlp = spacy.load("en_core_web_sm")
doc = nlp("I love coffee") # Original Doc
print(doc.vocab.strings["coffee"]) # 3197928453018144401
print(doc.vocab.strings[3197928453018144401]) # 'coffee' 👍
empty_doc = Doc(Vocab()) # New Doc with empty Vocab
# empty_doc.vocab.strings[3197928453018144401] will raise an error :(
empty_doc.vocab.strings.add("coffee") # Add "coffee" and generate hash
print(empty_doc.vocab.strings[3197928453018144401]) # 'coffee' 👍
new_doc = Doc(doc.vocab) # Create new doc with first doc's vocab
print(new_doc.vocab.strings[3197928453018144401]) # 'coffee' 👍
```
If the vocabulary doesn't contain a string for `3197928453018144401`, spaCy will
raise an error. You can re-add "coffee" manually, but this only works if you
actually _know_ that the document contains that word. To prevent this problem,
spaCy will also export the `Vocab` when you save a `Doc` or `nlp` object. This
will give you the object and its encoded annotations, plus the "key" to decode
it.
## Serialization {#serialization}
import Serialization101 from 'usage/101/\_serialization.md'
To learn more about how to **save and load your own pipelines**, see the usage
guide on [saving and loading](/usage/saving-loading#models).
## Training {#training}
import Training101 from 'usage/101/\_training.md'
To learn more about **training and updating** pipelines, how to create training
data and how to improve spaCy's named entity recognition models, see the usage
guides on [training](/usage/training).
## Language data {#language-data}
import LanguageData101 from 'usage/101/\_language-data.md'
## Community & FAQ {#community-faq}
We're very happy to see the spaCy community grow and include a mix of people
from all kinds of different backgrounds – computational linguistics, data
science, deep learning, research and more. If you'd like to get involved, below
are some answers to the most important questions and resources for further
reading.
### Help, my code isn't working! {#faq-help-code}
Bugs suck, and we're doing our best to continuously improve the tests and fix
bugs as soon as possible. Before you submit an issue, do a quick search and
check if the problem has already been reported. If you're having installation or
loading problems, make sure to also check out the
[troubleshooting guide](/usage/#troubleshooting). Help with spaCy is available
via the following platforms:
> #### How do I know if something is a bug?
>
> Of course, it's always hard to know for sure, so don't worry – we're not going
> to be mad if a bug report turns out to be a typo in your code. As a simple
> rule, any C-level error without a Python traceback, like a **segmentation
> fault** or **memory error**, is **always** a spaCy bug.
>
> Because models are statistical, their performance will never be _perfect_.
> However, if you come across **patterns that might indicate an underlying
> issue**, please do file a report. Similarly, we also care about behaviors that
> **contradict our docs**.
- [Stack Overflow](https://stackoverflow.com/questions/tagged/spacy): **Usage
questions** and everything related to problems with your specific code. The
Stack Overflow community is much larger than ours, so if your problem can be
solved by others, you'll receive help much quicker.
- [Gitter chat](https://gitter.im/explosion/spaCy): **General discussion** about
spaCy, meeting other community members and exchanging **tips, tricks and best
practices**.
- [GitHub issue tracker](https://github.com/explosion/spaCy/issues): **Bug
reports** and **improvement suggestions**, i.e. everything that's likely
spaCy's fault. This also includes problems with the trained pipelines beyond
statistical imprecisions, like patterns that point to a bug.
Please understand that we won't be able to provide individual support via email.
We also believe that help is much more valuable if it's shared publicly, so that
**more people can benefit from it**. If you come across an issue and you think
you might be able to help, consider posting a quick update with your solution.
No matter how simple, it can easily save someone a lot of time and headache –
and the next time you need help, they might repay the favor.
### How can I contribute to spaCy? {#faq-contributing}
You don't have to be an NLP expert or Python pro to contribute, and we're happy
to help you get started. If you're new to spaCy, a good place to start is the
[`help wanted (easy)` label](https://github.com/explosion/spaCy/issues?q=is%3Aissue+is%3Aopen+label%3A"help+wanted+%28easy%29")
on GitHub, which we use to tag bugs and feature requests that are easy and
self-contained. We also appreciate contributions to the docs – whether it's
fixing a typo, improving an example or adding additional explanations. You'll
find a "Suggest edits" link at the bottom of each page that points you to the
source.
Another way of getting involved is to help us improve the
[language data](/usage/adding-languages#language-data) – especially if you
happen to speak one of the languages currently in
[alpha support](/usage/models#languages). Even adding simple tokenizer
exceptions, stop words or lemmatizer data can make a big difference. It will
also make it easier for us to provide a trained pipeline for the language in the
future. Submitting a test that documents a bug or performance issue, or covers
functionality that's especially important for your application is also very
helpful. This way, you'll also make sure we never accidentally introduce
regressions to the parts of the library that you care about the most.
**For more details on the types of contributions we're looking for, the code
conventions and other useful tips, make sure to check out the
[contributing guidelines](%%GITHUB_SPACY/CONTRIBUTING.md).**
spaCy adheres to the
[Contributor Covenant Code of Conduct](http://contributor-covenant.org/version/1/4/).
By participating, you are expected to uphold this code.
### I've built something cool with spaCy – how can I get the word out? {#faq-project-with-spacy}
First, congrats – we'd love to check it out! When you share your project on
Twitter, don't forget to tag [@spacy_io](https://twitter.com/spacy_io) so we
don't miss it. If you think your project would be a good fit for the
[spaCy Universe](/universe), **feel free to submit it!** Tutorials are also
incredibly valuable to other users and a great way to get exposure. So we
strongly encourage **writing up your experiences**, or sharing your code and
some tips and tricks on your blog. Since our website is open-source, you can add
your project or tutorial by making a pull request on GitHub.
If you would like to use the spaCy logo on your site, please get in touch and
ask us first. However, if you want to show support and tell others that your
project is using spaCy, you can grab one of our **spaCy badges** here:
```markdown
[](https://spacy.io)
```
```markdown
[](https://spacy.io)
```
```markdown
[](https://spacy.io)
```
```markdown
[](https://spacy.io)
```