doccano
Open source text annotation tool for machine learning
About doccano
doccano is an open-source, web-based annotation tool for machine learning practitioners. It supports text classification, sequence labeling, and sequence-to-sequence tasks, making it ideal for building labeled datasets for NLP models like sentiment analysis, named entity recognition, and text summarization.
Pros & Cons
Pros
- Completely free and open source with no usage limits or premium tiers
- Simple, intuitive web interface accessible to non-technical annotators
- Supports all major NLP annotation tasks (classification, NER, seq2seq)
- Easy setup with Docker or pip — can be running in minutes
- REST API enables automation and integration with ML pipelines
- Active open-source community with regular updates
Cons
- No built-in PDF annotation support — requires external OCR preprocessing
- Basic quality control — lacks built-in inter-annotator agreement metrics
- No adjudication UI for resolving disagreements between annotators
- Limited to text-based annotation — no image or audio annotation support
- Self-hosted only — no managed cloud offering available
Key Features
Text Classification
Label documents with categories for sentiment analysis, topic classification, and spam detection tasks
Sequence Labeling
Annotate entities within text for named entity recognition (NER), part-of-speech tagging, and chunking
Sequence-to-Sequence
Create paired text annotations for machine translation, text summarization, and paraphrase generation
Team Collaboration
Multiple annotators can work concurrently on the same project with role-based access control
REST API
Programmatic access for data upload, annotation export, and importing model predictions for pre-labeling
Multi-Format Import/Export
Support for various data formats including JSON, JSONL, CSV, CoNLL, and plain text
Quick Setup
Create a project, upload data, and start annotating in minutes with Docker or pip install
Pricing
- All features included
- Self-hosted
- Unlimited projects
- Unlimited annotators
- REST API access
- Community support
Best For
NLP Model Training
Create labeled datasets for training custom NLP models including sentiment analysis, NER, and text classification
Research Data Annotation
Academic and research teams annotating text corpora for linguistics, social science, and medical NLP studies
ML Pipeline Integration
Use the REST API to integrate annotation workflows into automated machine learning pipelines with pre-labeling support
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