Text Labelling Made Simple With How To Guide & Tools List

by | Sep 21, 2023 | Data Science, Natural Language Processing

What is text labelling?

Text labelling, or text annotation or tagging, assigns labels or categories to text data to make it more understandable and usable for various natural language processing (NLP) tasks. Text labelling is crucial in training machine learning models for text classification, sentiment analysis, named entity recognition, and more tasks.

A brief overview of some everyday text labelling tasks

  1. Text Classification: In text classification, each document or piece of text is assigned to one or more predefined categories or classes. For example, classifying emails as spam or not, categorizing news articles into topics like sports, politics, or entertainment, or sentiment analysis, where text is organized as positive, negative, or neutral.
  2. Named Entity Recognition (NER): NER involves identifying and classifying entities such as names of people, organizations, locations, dates, and other specific terms within a text. This helps in extracting structured information from unstructured text.
  3. Part-of-Speech (POS) Tagging: POS tagging assigns grammatical tags to each word in a sentence, indicating its role in the sentence structure, such as nouns, verbs, adjectives, etc.
  4. Sentiment Analysis: Sentiment analysis involves labelling text with sentiments or emotions, typically positive, negative, or neutral. This is often used in social media monitoring, product reviews, and customer feedback analysis.
  5. Topic Modeling: In topic modelling, text documents are labelled with topics or themes that they are related to. This helps in organizing and summarizing extensive collections of documents.
  6. Intent Classification: In chatbots and virtual assistants, the text is labelled with the intent of the user’s query so that the system can provide appropriate responses.

Text labelling can be done manually by human annotators or through automated methods. Manual annotation is often time-consuming and requires human expertise, but it is crucial for creating high-quality labelled datasets for training machine learning models.

Automated methods, such as rule-based approaches or distant supervision, can speed up the labelling process but may not consistently achieve the same level of accuracy as human annotation.

In text labelling and classification, each document or piece of text is assigned to one or more predefined categories or classes

In text classification, each document or piece of text is assigned to one or more predefined categories or classes.

Once text data is labelled, it can be used to train and evaluate machine learning models, enabling them to make predictions, extract information, or perform other NLP tasks based on the labelled information.

What is the difference between text labelling and annotating?

Text labelling and annotating are closely related concepts in natural language processing (NLP) and data analysis, but they refer to slightly different processes and tasks. Here’s a comparison of text labeling vs. annotating:

What is Text Labeling?

Text labelling involves the assignment of predefined labels or categories to specific sections of text data, often intending to categorize or classify the text based on these labels.

Task Examples:

  • Labelling movie reviews as “positive,” “negative,” or “neutral” for sentiment analysis.
  • Categorizing news articles into topics like “sports,” “politics,” or “entertainment.”
  • Tagging entities like names of people, organizations, and locations in a text document (named entity recognition).

Methodology: Text labelling is typically done using guidelines that define the criteria for assigning labels to text, and it can be performed manually by human annotators or through automated methods.

Use Cases: Text labelling is commonly used for supervised machine learning tasks where labelled data is required to train and evaluate models. It’s essential for classification, information extraction, and various NLP tasks.

What is Text Annotation?

Text annotation is a broader term encompassing adding additional information, metadata, or context to a text. Annotation can include labelling but also covers a broader range of activities.

Task Examples:

  • Highlighting and marking specific text parts to indicate their importance or relevance.
  • Adding comments or explanations to text for clarity or to provide additional context.
  • Associating multimedia elements like images, videos, or links with text passages.

Methodology: Text annotation is not limited to labelling; it can involve various activities beyond classification. Annotation can be done manually or with automated tools, depending on the specific task.

Use Cases: Text annotation is used in various contexts, including text analysis, data organization, information retrieval, and document management. It’s not limited to machine learning but can enhance data understanding and accessibility.

Text labelling is a specific subtask within text annotation. While labelling involves categorizing text data into predefined classes or categories, text annotation encompasses a broader set of activities, including labelling but extending to adding metadata, context, or comments to enrich the understanding and utility of text. Both text labelling and text annotation are essential processes in NLP and data analysis, serving different purposes depending on the task at hand.

Automated and Semi-Automated Labelling

Automated and semi-automated labelling techniques have become increasingly valuable in efficiently handling large-scale labelling tasks. This section will explore these approaches and how they aid labelling processes.

1. Automated Labeling:

  • Rule-Based Labeling: Create predefined rules or patterns to label text based on specific criteria automatically. For instance, you can use regular expressions to identify email addresses, phone numbers, or URLs in text.
  • Dictionary-Based Labeling: Utilize dictionaries or lexicons to match words or phrases in the text with predefined categories or labels. This is commonly used in sentiment analysis, where words are associated with positive or negative sentiments.
  • Machine Learning Models: Train machine learning models to predict labels for text data. For instance, you can use pre-trained models for named entity recognition (NER) or text classification. Fine-tuning these models on your specific data can further improve accuracy.

2. Semi-Automated Labeling:

  • Active Learning: Implement active learning strategies to prioritize which examples should be labelled by human annotators. Algorithms select examples the model is uncertain about, improving model performance while reducing the need for extensive human labelling.
  • Human-in-the-Loop Labeling: Combine human expertise with automated processes. Annotators review and correct labels generated by automated methods, ensuring high-quality data.
  • Bootstrapping: Start with a small set of manually labelled data and expand iteratively. Use this growing dataset to train and improve automated labelling models. This approach is effective for named entity recognition and relation extraction tasks.

3. Hybrid Approaches:

  • Consider hybrid approaches that blend automated and human labelling. Combining the strengths of both paths can lead to efficient and accurate results, particularly in complex tasks like named entity recognition and entity linking.

Automated and semi-automated labelling approaches are powerful tools for managing the challenges of labelling large and diverse text datasets. By carefully designing workflows incorporating human expertise and automation, you can accelerate the labelling process, reduce costs, and maintain high data quality, ultimately leading to more effective machine learning models and NLP applications.

Challenges and Considerations:

  • Data Quality: Automated labelling can introduce errors if not carefully designed and validated. Regularly assess the quality of automated labels and make necessary corrections.
  • Human Oversight: Maintain human oversight and intervention to handle ambiguous cases and ensure the correctness of labels.
  • Feedback Loop: Establish a feedback loop where annotators review and provide feedback on automated labels. This iterative process helps train models to improve over time.
  • Scalability: Leverage automated techniques for large-scale datasets, but be cautious about their limitations and adapt the approach as needed for specific use cases.

Top text labelling tools

Text labelling tools are software applications that help data analysts label text data according to specific techniques. This can include tasks such as named entity recognition (NER), sentiment analysis, topic classification, and relationship extraction.

Text labelling tools are essential for training machine learning models to perform natural language processing (NLP) tasks. By labelling data, data analysts can provide the models with the ground truth information they need to learn to perform these tasks accurately.

Various text labelling tools are available, both free and paid. Some of the most popular text labelling tools are:

  • Labelbox is a cloud-based text labelling tool that offers a variety of features, including pre-trained models for NER, sentiment analysis, and topic classification.
  • Doccano is an open-source text labelling tool that is easy to use and deploy. It offers a variety of features for labelling text data, including NER, sentiment analysis, and topic classification.
  • Prodigy is a paid text labelling tool known for its flexibility and powerful features. It can label text data, including NER, sentiment analysis, topic classification, and relationship extraction.
  • brat is an open-source text labelling tool popular in the academic community. It offers a variety of features for labelling text data, including NER, sentiment analysis, and relationship extraction.

If you are new to text labelling, starting with a free and easy-to-use tool like Doccano is recommended. Once you have gained some text labelling experience, you can consider switching to a more powerful tool, such as Labelbox or Prodigy.

Additional tips for choosing and using a text labelling tool

  • Make sure the tool supports the types of text labelling tasks you need to perform. Not all text labelling tools support the same kinds of tasks. For example, some tools may only support NER, while others may support a broader range of tasks, such as sentiment analysis, topic classification, and relationship extraction.
  • Choose a tool with the features you need. Some text labelling tools offer a variety of features, such as pre-trained models, collaboration features, and data quality control features. Consider the features that are important to you when choosing a tool.
  • Consider your budget. Text labelling tools can range in price from free to several thousand dollars annually. Choose a tool that fits your budget.
  • Read reviews of different text labelling tools before making a decision. This can help you learn more about the strengths and weaknesses of various tools.
  • Start with a free trial or demo before committing to a paid tool. This will allow you to try the tool and see if it is correct.

Once you have chosen a text labelling tool, you can start labelling your text data. Be sure to follow the instructions provided by the tool to ensure that your labels are accurate and consistent.

How to implement text labelling in Python

Text labelling in Python can be accomplished using various libraries and techniques, depending on the specific text labelling task you need to perform. Here, I’ll provide a general overview of how to do text labelling for a few everyday tasks:

Text Classification

Text classification involves assigning predefined labels or categories to text documents. You can use Python and popular libraries like scikit-learn for this task. Here’s a simplified example of binary text classification:

from sklearn.feature_extraction.text import CountVectorizer
from sklearn.model_selection import train_test_split
from sklearn.naive_bayes import MultinomialNB

# Sample text data and labels
texts = ["Text 1", "Text 2", ...]
labels = [0, 1, ...]  # 0 for one class, 1 for another class

# Vectorize the text data
vectorizer = CountVectorizer()
X = vectorizer.fit_transform(texts)

# Split data into training and testing sets
X_train, X_test, y_train, y_test = train_test_split(X, labels, test_size=0.2, random_state=42)

# Train a classifier
classifier = MultinomialNB()
classifier.fit(X_train, y_train)

# Make predictions
predictions = classifier.predict(X_test)

You can replace the MultinomialNB classifier with other algorithms like Support Vector Machines, Random Forests, or deep learning models.

Named Entity Recognition (NER)

Named Entity Recognition involves identifying and labelling entities in text. You can use libraries like spaCy or NLTK for NER tasks:

import spacy

# Load the spaCy NER model
nlp = spacy.load("en_core_web_sm")

# Sample text
text = "Apple Inc. is a technology company based in Cupertino, California."

# Process the text
doc = nlp(text)

# Extract named entities and labels
for ent in doc.ents:
    print(ent.text, ent.label_)

SpaCy provides various pre-trained models for multiple languages, and you can also train custom NER models if needed.

Sentiment Analysis

Sentiment analysis involves classifying text as positive, negative, or neutral. You can use pre-trained models like TextBlob:

from textblob import TextBlob

# Sample text
text = "I love this product. It's amazing!"

# Perform sentiment analysis
analysis = TextBlob(text)

# Get sentiment polarity (-1 to 1: negative to positive)
sentiment = analysis.sentiment.polarity

if sentiment > 0:
    print("Positive sentiment")
elif sentiment < 0:
    print("Negative sentiment")
    print("Neutral sentiment")

You can also use more advanced sentiment analysis models like those provided by the Hugging Face Transformers library for fine-grained sentiment analysis.

These are just basic examples to get you started. Depending on your specific task and dataset, you may need to preprocess text data, perform feature engineering, and fine-tune models for optimal performance. Deep learning frameworks like TensorFlow and PyTorch offer flexibility and scalability for more complex NLP tasks.

Challenges and Pitfalls

Text labelling is crucial in natural language processing (NLP) and machine learning. Still, it comes with challenges and potential pitfalls that can affect the quality of labelled data and the performance of your models. In this section, we’ll explore some of the common challenges and pitfalls associated with text labelling:

1. Ambiguity in Language:

  • Challenge: Language is inherently ambiguous; text often contains sentences or phrases with multiple interpretations.
  • Pitfall: Annotators may make subjective judgments, leading to inconsistent labelling. Ambiguity can also result in models making incorrect predictions.

2. Context Dependency:

  • Challenge: The meaning of a word or phrase can change based on the context in which it appears.
  • Pitfall: Annotators may overlook or misinterpret context, leading to mislabeled data. Models trained on such data may struggle with context-dependent tasks.

3. Bias and Stereotyping:

  • Challenge: Annotators may unknowingly introduce bias or stereotypes into the labelling process, which can propagate into machine learning models.
  • Pitfall: Biased data can lead to biased models that produce unfair or discriminatory results.

4. Subjectivity and Inter-Annotator Variability:

  • Challenge: Different annotators may have varying interpretations and subjective opinions, leading to label discrepancies.
  • Pitfall: Low inter-annotator agreement can result in unreliable labelled data and reduce the model’s accuracy.

5. Labeling Rare and Uncommon Entities:

  • Challenge: Identifying and labelling rare or infrequently occurring entities in the text can be challenging, mainly when annotators have limited exposure to them.
  • Pitfall: Underrepresentation of rare entities in labelled data can lead to poor model performance for those entities.

6. Scalability and Cost:

  • Challenge: Scaling up text labelling for large datasets can be time-consuming and expensive when using human annotators.
  • Pitfall: Limited resources may lead to inadequate labelling or force compromises on the quality of annotations.

7. Ambiguous Guidelines:

  • Challenge: Incomplete or unclear labelling guidelines can confuse annotators and result in inconsistent annotations.
  • Pitfall: Lack of clarity in policies can lead to errors and additional rounds of annotation.

8. Handling Negations and Double Negatives:

  • Challenge: Detecting negations (e.g., “not good”) and double negatives can be complex and context-dependent.
  • Pitfall: Mislabeling negated text can flip the sentiment or meaning, causing errors in sentiment analysis and other tasks.

9. Long and Complex Texts:

  • Challenge: Annotating long and complex documents or texts with multiple labels can be time-consuming and prone to oversights.
  • Pitfall: Incomplete or inaccurate annotations in lengthy documents can impact model performance.

10. Maintaining Consistency Over Time: 

  • Challenge: Consistency in labelling practices as annotators change or guidelines evolve can be a long-term challenge.
  • Pitfall: Inconsistencies in annotations over time can affect model stability and require ongoing quality control.

11. Inadequate Evaluation Metrics:

  • Challenge: Choosing appropriate evaluation metrics for text labelling tasks can be challenging.
  • Pitfall: Using improper metrics may not reflect the actual quality of labelled data and model performance.

Awareness of these challenges and pitfalls is the first step in mitigating them. Addressing these issues requires careful planning, clear communication with annotators, ongoing quality control, and, in some cases, automated tools and techniques to improve the reliability and consistency of labelled data. By proactively tackling these challenges, you can enhance the effectiveness of your text labelling efforts and the overall success of your NLP projects.


In natural language processing (NLP) and machine learning, text labelling bridges unstructured text data and intelligent, data-driven applications. This comprehensive guide explored the fundamental aspects of text labelling, from its significance and various tasks to best practices, challenges, and incorporating automated and semi-automated techniques. As we conclude, let’s recap the key takeaways and the broader impact of text labelling:

The Power of Text Labeling:

  • Text labelling is the cornerstone of NLP, enabling machines to understand, classify, and extract valuable insights from textual data.

Text Labeling Tasks:

  • We’ve delved into standard text labelling tasks such as text classification, named entity recognition (NER), sentiment analysis, and more, each with unique challenges and applications.

Best Practices for Success:

  • Establishing clear guidelines, ensuring annotator training, maintaining consistency, and addressing bias are essential best practices for producing high-quality labelled data.

Challenges and Pitfalls:

  • Text labelling has difficulties, including ambiguity, context dependency, bias, and scalability issues. Awareness of these challenges is the first step toward mitigation.

Automated and Semi-Automated Labeling:

  • We’ve explored the use of automation, from rule-based approaches to machine learning models, and how they can complement human labelling efforts. Hybrid processes and data annotation platforms offer efficient solutions.

Real-World Impact:

  • Text labelling is more than just a technical task; it profoundly impacts applications such as chatbots, sentiment analysis for customer feedback, information extraction for research, and more.

In conclusion, text labelling is both an art and a science, requiring a delicate balance between human judgment and automated precision. As you embark on your text labelling journey, remember that the quality of labelled data is the bedrock upon which powerful NLP models are built.

By applying the best practices, staying vigilant against pitfalls, and harnessing the potential of automation, you’ll advance your NLP projects and contribute to the ever-expanding landscape of human-computer interaction, understanding, and communication. Text labelling is the key that unlocks the vast potential of language in the digital age.

About the Author

Neri Van Otten

Neri Van Otten

Neri Van Otten is the founder of Spot Intelligence, a machine learning engineer with over 12 years of experience specialising in Natural Language Processing (NLP) and deep learning innovation. Dedicated to making your projects succeed.

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