21 best annotation tools for documents, video, and more

In today’s data-driven world, annotation tools have become indispensable for various tasks, ranging from data labeling and content review to collaborative editing and research analysis. 

These tools empower users to add comments, highlights, and annotations to different types of content, enabling enhanced organization, collaboration, and understanding.

In this article, we will explore the top 21 annotation tools that cater to different purposes and domains.

What are annotation tools?

Annotation tools are software applications or platforms designed to facilitate the process of adding comments, highlights, or other annotations to various types of content. These tools play a crucial role in tasks such as data annotation, document review, collaborative editing, and research analysis. 

Annotation tools offer a range of features and functionalities that let users mark specific sections of text, images, videos, or documents for further context, explanation, or reference.

Types of annotation tools

There are various different types of annotation tools on the market that cater to specific needs. 

Here’s a list of the seven most common types of annotation tools: 

1. Data annotation tools – these tools allow users to highlight, underline, strikethrough, or add comments to text-based content
2. Image annotation tools – annotate images by adding text, shapes, or drawings
3. Video annotation tools – annotate videos frame by frame, marking objects, actions, or events
4. Audio annotation tools – annotate audio files by adding markers, tags, or comments at specific timestamps or sections
5. Web annotation tools – annotate web pages or online documents, facilitating collaborative research and discussions
6. Document annotation tools – annotate academic papers, research, articles, and more
7. Code annotation tools – add comments, explanations, or documentation within source code files

Our shortlist of the top three annotation tools

Annotation tools can serve various different purposes. Here’s a closer look into the top three annotation tools that offer a comprehensive set of features from different fields of annotation.

1. Filestage – the best annotation tool for reviewing various file formats

Filestage is a review and feedback tool that makes it simple to collaborate on PDF documents, share videos, graphics, and marketing projects in general. 

It offers project managers a wide range of annotation and proofing features, which makes it easy for your internal and external key stakeholders to leave and discuss logical in-context feedback in real time.

A range of workflow features will make sure that you never miss a deadline or a game-changing suggestion. Next to custom pricing options, Filestage offers a Free plan – so you can check out the markup software at no risk.

And with the ability to integrate Filestage with Microsoft Teams, Jira, Adobe Premiere Pro, and a bunch of other tools, it fits in perfectly with your tool stack.

Key features

• Collaborative video annotation – Filestage enables multiple stakeholders to review and annotate various file types, including images, videos, and documents, in a centralized platform
• Review workflow management – It offers customizable workflows and task assignments, facilitating seamless collaboration and efficient annotation processes
• Commenting and markup tools – Users can leave comments, draw annotations, and highlight specific areas within files to provide feedback and suggestions
• Document version control – Filestage keeps track of file versions, allowing reviewers to compare changes and annotations over time
• Approval and feedback management – It provides features for approving or rejecting annotations and consolidating feedback from multiple reviewers

2. Labelbox

Labelbox is a popular data annotation platform that offers a wide range of annotation capabilities for images, videos, and text. It provides an intuitive interface for annotating and labeling data, along with powerful collaboration and project management features.

Labelbox supports various annotation types, including bounding boxes, polygons, keypoints, and semantic segmentation. It also offers automation features like active learning and model-assisted labeling.

Key features

• Data annotation – Labelbox supports a range of annotation types, including bounding boxes, polygons, semantic segmentation, and keypoint annotations, for various data types such as images, videos, and text
• Collaboration and review – It allows teams to collaborate on annotation projects, review annotations, and manage annotation quality control.
• Automation and active learning – Labelbox offers features for automating certain annotation tasks using pre-trained models and implementing active learning techniques to reduce annotation efforts
• Workflow management – users can create customized annotation workflows, assign tasks, and track the progress of annotation projects
• Integration and deployment – Labelbox provides integration with popular machine learning frameworks and cloud storage platforms for seamless data management and model deployment

3. SuperAnnotate

SuperAnnotate is a versatile and feature-rich data annotation platform that caters to image and video annotation needs. It offers a user-friendly interface with advanced annotation tools for bounding boxes, polygons, key points, and semantic segmentation.

SuperAnnotate provides powerful automation capabilities, including AI-assisted annotation and collaborative review workflows. It also offers integrations with popular machine-learning frameworks and platforms.

Key features

• Advanced annotation tools – SuperAnnotate offers a wide range of annotation tools and techniques, including bounding boxes, polygons, keypoint detection, instance segmentation, and semantic segmentation
• Collaboration and review – It enables real-time collaboration among team members, allowing them to review and validate annotations together
• Quality control – SuperAnnotate provides tools for quality control, such as metrics calculation, consensus review, and inter-annotator agreement analysis
• Automation and AI assistance – The platform uses AI to accelerate annotation tasks, improve annotation efficiency, and reduce human error
• Project management and versioning – SuperAnnotate offers project management features, version control, and comparison tools for managing and tracking annotation projects

Best data annotation tools

Data annotation tools are software applications or platforms specifically designed to assist in the process of annotating or labeling data.

Here are the top two data annotation tools available on the market:

1. Amazon SageMaker Ground Truth

SageMaker Ground Truth is a data annotation tool provided by Amazon Web Services (AWS). It simplifies the process of creating high-quality labeled datasets for machine learning models. It offers a scalable and customizable platform for annotation tasks, supporting both automated and human-in-the-loop labeling.

SageMaker Ground Truth supports various annotation types, such as bounding boxes, semantic segmentation, and text classification. It integrates seamlessly with other AWS services, making it convenient for end-to-end machine learning workflows.

Key features

• Customizable annotation workflows – It allows users to create custom annotation workflows tailored to specific data types and annotation tasks
• Human-in-the-loop annotation – It combines automated annotation with human review, providing mechanisms to review and improve machine-generated annotations
• Scalability – The tool is designed to handle large-scale annotation projects
• Active learning – It supports active learning techniques to intelligently select samples for annotation and optimizes the annotation process
• Integration with Amazon Services – It seamlessly integrates with other Amazon Web Services (AWS) products, such as Amazon Rekognition, for enhanced annotation capabilities

2. SuperAnnotate

SuperAnnotate is a versatile and feature-rich data annotation platform that caters to image and video annotation needs. It offers a user-friendly interface with advanced annotation tools for bounding boxes, polygons, keypoints, and semantic segmentation.

SuperAnnotate provides powerful automation capabilities, including AI-assisted annotation and collaborative review workflows. It also offers integrations with popular machine learning frameworks and platforms.

Key features

• Advanced annotation tools
• Collaboration and review
• Quality control
• Automation and AI assistance
• Project management and versioning

Image annotation tools

Image annotation tools allow you to annotate images by adding bounding boxes, polygons, keypoints, or semantic segmentation masks to identify objects or regions of interest within the image.

Here are the two most popular image annotation tools:

1. RectLabel

RectLabel is a powerful visual object tagging tool specifically designed for object detection and localization tasks. It provides an intuitive interface with robust image annotations, including bounding boxes, polygons, lines, and keypoints.

RectLabel supports automatic annotation suggestions and offers features like image segmentation, instance tracking, and batch processing. It also integrates seamlessly with popular machine learning frameworks like TensorFlow and PyTorch.

Key features

• Image annotation – RectLabel focuses on image annotation and offers tools for bounding box annotation, segmentation masks, keypoints, and text annotations
• Object tracking – It provides features for object tracking within videos, allowing users to annotate objects across frames and track their movement
• Collaboration and versioning – RectLabel supports collaboration among team members and keeps track of annotations and changes across versions of the data
• Customizable annotation tools – Users can customize annotation tools and labels to match their specific annotation requirements and workflow
• Export formats – RectLabel allows users to export annotations in various formats, including Pascal VOC, COCO, YOLO, and TensorFlow Object Detection API

2. VGG Image Annotator (VIA)

VIA is a versatile and open-source image annotation tool developed by the Visual Geometry Group at the University of Oxford. It supports annotation of various shapes, including points, polygons, rectangles, and ellipses.

VIA allows for annotating images individually or in batches, and it supports exporting annotations in multiple formats. It also offers customizability and extensibility, making it suitable for research and specialized annotation requirements.

Key features

• Multi-format support – VIA supports a wide range of image formats, allowing users to annotate images in formats such as JPEG, PNG, and GIF
• Multiple annotation types – It provides various annotation types, including bounding boxes, polygons, keypoints, and region descriptions, to annotate objects and regions of interest within images
• Collaboration and version control – VIA supports collaborative annotation, allowing multiple users to work on the same set of images simultaneously
• Annotation import/export – VIA allows users to import and export annotations in different formats, including JSON, CSV, and VIA project files
• Customization and automation – VIA offers customization options, such as custom attribute definitions, and allows users to apply pre-trained models for automated annotation

Video annotation tools

As the name suggests, video annotation tools are used to add additional information on videos. This means that you can mark objects, track movements, or label frames.

Here are the two best annotation tools on the market:

1. Video Annotation Tool from Internet Curation (VATIC)

VATIC is a popular open-source video annotation tool developed by the Computer Vision Group at Stanford University. It offers an intuitive web-based interface for annotating videos frame by frame. Users can draw bounding boxes, track objects, and add labels or attributes to the annotated regions. VATIC supports collaboration, allowing multiple annotators to work on the same video simultaneously.

Key features

• Video annotation capabilities – VATIC focuses specifically on video annotation, allowing users to annotate objects, track their movements, and draw on videos
• Collaborative annotation – It supports collaborative annotation workflows, enabling multiple users to annotate videos and review annotations together.
• Tracking and object identification – VATIC provides tools for object tracking, allowing users to annotate objects across frames and track their trajectories
• Review and quality control – The tool offers review and validation features
• Project management – VATIC includes project management features, such as task assignment and progress tracking

2. Computer Vision Annotation Tool (CVAT)

CVAT is a powerful open-source video annotation tool developed by Intel. It supports annotation for a wide range of tasks, including object detection, tracking, and segmentation. CVAT allows users to annotate videos by drawing bounding boxes, polygons, polylines, or points.

It offers collaborative annotation, synchronization across multiple annotators, and detailed annotation statistics. CVAT also provides automation features like interpolation, semi-automatic annotation, and inference integration.

Key features

• Wide range of annotation types – CVAT supports diverse annotation types
• Collaborative annotation and review – It enables real-time collaboration among team members, by collectively annotating and reviewing data
• Automatic annotation – CVAT offers AI-based assistance to accelerate annotation tasks and reduce manual effort
• Advanced video annotation features – CVAT provides comprehensive video annotation capabilities, including object tracking, video segmentation, and frame-level annotation
• Integration and deployment –The tool allows integration with deep learning frameworks and supports exporting annotations in formats compatible with popular machine learning libraries

Audio annotation tools

When looking into different audio annotation tools, you should consider all the file formats it supports, and whether it’s designed for more complex annotation tasks.

Here are the top two audio annotation tools with comprehensive set of audio annotation features:

1. EUDICO Linguistic Annotator (ELAN)

ELAN is a powerful and widely used audio annotation tool developed by the Max Planck Institute for Psycholinguistics. It offers a comprehensive set of features for annotating audio and video recordings.

ELAN allows users to create and edit time-aligned annotations for multiple tiers, such as transcriptions, translations, and linguistic analysis. It supports various audio formats, offers advanced search and analysis capabilities, and is suitable for linguistic research and complex annotation tasks.

Key features

• Linguistic annotation – ELAN is specifically designed for linguistic annotation, enabling users to annotate speech, language, and gesture data
• Multi-layer Annotation – It supports multiple layers of annotation, allowing users to create and align annotations at different linguistic or temporal levels
• Time-aligned annotations – ELAN provides precise time alignment for annotations
• Metadata and transcription – The tool allows users to add metadata, transcriptions, and descriptive information to annotations, providing contextual information
• Annotation visualization and analysis – ELAN offers visualization and analysis tools to explore and analyze linguistic annotations and their relationships

2. Praat

Praat is a versatile and popular tool for audio annotation and analysis. It provides a wide range of features for manipulating and annotating audio recordings. Praat allows users to create annotations, transcriptions, and phonetic labels at various time points.

It offers visualization tools, signal processing capabilities, and scripting options for advanced customization. Praat is widely used in phonetics, speech analysis, and linguistic research.

Key features

• Speech and phonetics annotation – Praat is a specialized tool for speech and phonetics analysis, providing annotation features for audio recordings and linguistic analysis
• Waveform and spectrogram visualization – It offers visualizations of audio waveforms and spectrograms to facilitate detailed analysis and annotation
• Annotation types – Praat supports various annotation types, including segment labels, point labels, interval labels, and boundary labels, for precise annotation of speech data
• Scripting and automation – The tool allows users to create scripts to automate repetitive annotation tasks or perform advanced analyses
• Acoustic analysis – Praat allows users to extract and analyze acoustic features from speech data

3. Audacity

Although primarily known as an audio editing tool, Audacity also includes basic annotation features. It allows users to select specific regions of audio and add labels, comments, or markers.

While Audacity’s annotation capabilities may not be as extensive as dedicated annotation tools, it can be a convenient option for simple audio annotation tasks or when combined with its audio editing functionalities.

Key features

1. Audio recording and editing – Audacity allows users to record, import, and edit audio files with a range of editing capabilities, including cut, copy, paste, and apply effects
2. Multi-track editing – It supports multi-track editing, allowing users to work with multiple audio tracks simultaneously, adjust levels, and create complex audio compositions
3. Effects and plugins – audacity offers a wide range of built-in audio effects, such as reverb, equalization, and noise reduction
4. Spectrogram analysis – It provides a spectrogram view that displays the frequency and intensity of audio over time, allowing users to visualize and analyze audio characteristics
5. Cross-platform and open source – Audacity is a free and open-source tool available for Windows, macOS, and Linux, making it accessible to users across different operating systems

Web annotation tools

When it comes to annotating a web page, it’s best to turn to a specialized web annotation software.

Here are three great examples of web annotation tools:

1. Hypothesis

Hypothesis is a popular web annotation tool that allows users to annotate web pages and PDF documents. It offers a browser extension that enables users to highlight text, add comments, and create discussions within the context of the webpage. Hypothesis supports public and private annotations, collaboration features, and integration with learning management systems. It promotes open annotation standards and interoperability.

Key features

1. Web annotation – Hypothesis allows users to annotate web pages, documents, and digital content, making it easy to highlight, comment, and add notes directly on the content being viewed
2. Collaboration and discussion – It supports collaborative annotation, allowing users to engage in discussions, reply to annotations, and interact with other users’ annotations
3. Privacy and control – Hypothesis provides privacy controls, allowing users to choose whether their annotations are public or restricted to a specific group or audience
4. Integration with learning management systems (LMS) – It offers integration with popular LMS platforms, allowing educators to incorporate collaborative annotation activities into their online courses
5. API and customization – Hypothesis provides an API for developers to integrate annotation capabilities into their own applications or websites

2. Diigo

Diigo is a versatile web annotation and bookmarking tool that enables users to highlight, bookmark, and add sticky notes to web pages. It offers browser extensions for easy annotation and organization of online content.

Diigo supports social annotation functionality, sharing and collaboration options, and the ability to create private or public annotation groups. It also provides a personal library for managing annotated resources.

Key features

1. Web highlighting and sticky notes – You can add sticky notes directly on web pages to mark important information and save personal notes
2. Webpage bookmarking and organization – It allows users to bookmark webpages and save them in an organized manner with tags, folders, and search functionality for easy retrieval
3. Social annotation and collaboration – Diigo supports social annotation, allowing users to share their highlights, annotations, and bookmarks with others
4. Webpage archiving – It provides a webpage archiving feature, allowing users to capture and save a copy of webpages, even if the original page is modified or removed
5. Knowledge sharing and discovery – Diigo offers a platform for users to discover and explore content shared by others, expanding their knowledge base and staying updated with new information

3. Kami

Kami is a web-based annotation tool designed for collaboration and document annotation. It supports annotating PDF files, Google Drive documents, and web pages. Kami allows users to highlight text, add comments, draw shapes, and insert images within documents.

It offers real-time collaboration, sharing options, and integration with Google Classroom and learning management systems.

Key features

1. PDF annotation and markup – Kami allows users to annotate and markup PDF documents with tools for highlighting, underlining, adding comments, and drawing shapes
2. Collaboration and real-time editing – It supports real-time collaboration, enabling multiple users to work on the same document simultaneously and view each other’s annotations in real time
3. Document organization and management – Kami provides features for organizing and managing PDF documents, including file merging, splitting, and rearranging pages
4. Integration with Google Drive and Classroom – It offers integrations that allow you to easy access your files and create streamlined collaboration within the Google ecosystem
5. Accessibility and integration with assistive technology – Kami offers accessibility features, including support for screen readers and integration with other tools to enhance the accessibility of PDF documents

Document annotation tools

Unlike any AI and natural language processing annotation tools, document annotation tools have a completely different purpose. They allow you to mark certain areas of your document and leave in-context feedback on top.

Here’s a look into some of the best document annotation tools:

1. Adobe Acrobat

Adobe Acrobat is a widely used and feature-rich document annotation tool. It offers a comprehensive set of annotation tools, including highlighting, underlining, strikethrough, adding comments, and drawing shapes. Adobe Acrobat allows for collaboration and review workflows, supports form filling, and offers advanced features like redaction and document security. It is compatible with PDF documents and is available for both desktop and mobile devices.

Key features

• Comprehensive PDF editing features
• PDF form creation and fillable forms
• Document security and protection
• OCR (Optical Character Recognition)
• Integration with Adobe Creative Cloud

2. Xodo

Xodo is a versatile and user-friendly document annotation tool available on various platforms, including Windows, Mac, Android, and iOS. It provides a range of annotation tools, such as highlighting, underlining, adding text, shapes, and signatures. Xodo offers seamless syncing across devices, supports collaboration, and allows for document signing. It is particularly popular for its smooth and responsive user interface.

Key features

1. PDF annotation and markup
2. Collaboration and syncing
3. Document organization and management
4. PDF form filling and signing
5. Cloud storage integration

3. Nitro PDF

Nitro PDF is a robust document annotation tool that offers a wide array of annotation options. It enables users to highlight text, add comments, draw shapes, and apply stamps or signatures.

Nitro PDF supports collaboration and version control, and it provides advanced features like OCR (Optical Character Recognition) and PDF form creation. It is available for both Windows and Mac platforms.

Key features

• PDF creation and conversion
• PDF editing and annotation
• Collaboration and review features
• Document signing and security
• OCR capabilities to convert scanned documents into searchable and editable text

Code annotation tools

If you’re looking to review a code, then these are the tools for you. These tools offer features like code highlighting, commenting, and version control integration, making it easier to leave feedback and collaborate on source code.

Here are the two best code annotation software:

1. Visual Studio Code (VS Code)

VS Code is a popular and feature-rich code editor that offers built-in support for code annotation. It provides features like line commenting, block commenting, and the ability to add descriptive comments within code.

VS Code also supports extensions that enhance code annotation capabilities, such as adding tags, generating API documentation, or creating interactive code snippets.

Key features

• Rich code editing experience with features like syntax highlighting, auto-completion, and intelligent code suggestions
• Extensibility and customization options to tailor the environment to their specific needs
• Version control integration with version control systems like Git, providing tools for managing code repositories, tracking changes, and resolving conflicts
• Built-in debugging capabilities for various programming languages
• It includes an integrated terminal for executing commands and a task runner for automating repetitive tasks within the development workflow

2. Eclipse

Eclipse is a widely used integrated development environment (IDE) that includes comprehensive code annotation features.

It supports commenting at the line, block, or method level and provides options to generate Javadoc comments for Java code. Eclipse also offers refactoring tools and code analysis features that aid in maintaining code quality and documentation.

Key features

• Robust Java Development environment – Eclipse is renowned for its strong support for Java development, offering features like code completion, refactoring tools, and debugging capabilities
• Plugin Ecosystem – It boasts a vast ecosystem of plugins and extensions, allowing users to enhance Eclipse’s functionality for various programming languages and development purposes
• Project management and tools integration
• Debugging and profiling capabilities – It allows users to identify and resolve issues in their code and optimize performance with powerful debugging capabilities
• Collaboration and version control – Eclipse supports integration with version control systems like Git and provides features for collaborative development, code reviews, and team coordination

3. JetBrains IntelliJ IDEA

IntelliJ IDEA is a powerful IDE known for its extensive code annotation capabilities. It provides various features to add comments, generate Javadoc, and create code documentation. IntelliJ IDEA supports different programming languages, including Java, Kotlin, Python, and JavaScript.

It offers code inspections, auto-completion, and other intelligent features that facilitate effective code annotation.

Key features

• Intelligent code editor with features like code completion, intelligent code analysis, and smart suggestions
• Advanced refactoring tools that assist in restructuring code and improving its quality
• Built-in version control with systems like Git, Mercurial, and Subversion
• Productivity boosters, including features like code generation, live templates, quick-fix suggestions, and customizable code inspections to catch potential errors and improve coding speed
• Robust plugin ecosystem

Annotate your files for free with Filestage

Filestage is a free annotation tool that allows you to seamlessly leave feedback on top of PDF documents, videos, graphics, and marketing projects in general. 

With Filestage, you can create a smooth annotation process by allowing all important stakeholders to leave feedback and review files.

Filestage’s free version is designed for freelancers and smaller teams and includes:

• Unlimited files, versions, and reviewers
• 2 active projects
• 2 GB of storage
• 2 review steps
• Support for all file formats
• Integrations
• Due dates and reminders
• 3 sections
• Awaiting my review

Final thoughts

Various annotation tools are developed to cater to a wide range of purposes and industries. Whether you’re annotating images, videos, audio, code, or text content, these 21 annotation tools discussed in this article offer valuable features and capabilities to streamline your annotation workflows.If you’d like to see how Filestage can help you annotate various file formats and streamline your annotation process, make sure to try it for free →