Y Combinator W21
YC Winter 2021 developer tools companies
The data layer for physical AI
150 people · London, England, United Kingdom · Machine Learning, Robotics, Enterprise Software, Infrastructure · YC page
The OS for Embedded Telecom
150 people · San Francisco, CA, USA · Fintech, HR Tech, API, AI · YC page
Tools & infra to build and scale high-quality blockchain applications.
115 people · Miami, FL, USA · Developer Tools, Crypto / Web3, API · YC page
Frontend Platform for eCommerce
100 people · Warsaw, Masovian Voivodeship, Poland · Developer Tools, Open Source, E-commerce · YC page
Account-to-Account payments in Mexico and Chile.
60 people · Santiago, Santiago Metropolitan Region, Chile · Developer Tools, Fintech, Payments · YC page
AI Document Understanding API
60 people · Paris, Île-de-France, France · Deep Learning, Developer Tools, Automation, AI · YC page
Makes it easy for tech platforms to embed insurance into products
40 people · San Francisco, CA, USA · Developer Tools, Fintech, AI · YC page
Open source alternative to DataDog
38 people · San Francisco, CA, USA · Developer Tools, Open Source · YC page
Authorization Infrastructure securing AI at OpenAI, Zoom, & more
31 people · New York City, NY, USA · Developer Tools, Security, Open Source, Data Engineering · YC page
Shift FinOps Left: Proactively Find & Fix Cloud Cost Issues
25 people · Remote · Developer Tools, DevSecOps, FinOps, Open Source · YC page
The open source AI coding agent
24 people · Toronto, ON, Canada · Developer Tools, Open Source · YC page
Enterprise ready webhooks service, open-source and in the cloud
12 people · San Francisco, CA, USA · Developer Tools, Open Source, API · YC page
WeWeb is the AI app builder your IT team will approve.
12 people · Paris, Île-de-France, France · Developer Tools, Web Development · YC page
Open-source framework for building serverless applications
6 people · Zagreb, Croatia · Developer Tools, Open Source · YC page
Building the next generation of visual media
5 people · New York City, NY, USA · Video, Media, Infrastructure, AI · YC page
The notification inbox for web/mobile applications.
4 people · Barcelona, CT, Spain · Developer Tools · YC page
Better, faster tech vendor research
4 people · Los Angeles, CA, USA · Developer Tools · YC page
Communication and publishing tools for scientists
3 people · Calgary, AB, Canada · Documents, Developer Tools · YC page
Code review for DevOps tasks
3 people · São Paulo, SP, Brazil · Developer Tools, DevSecOps · YC page
Improving Developer Experience with Streamlined Code Reviews
2 people · Paris, Île-de-France, France · Developer Tools · YC page
Add powerful decision-making capabilities to any automated workflow.
2 people · San Francisco, CA, USA · Developer Tools, Workflow Automation, Enterprise Software · YC page
Configuration language for building enterprise web apps 10x faster
2 people · Zagreb, Croatia · Developer Tools, Open Source · YC page
Get up and running with large language models.
San Francisco, CA, USA · Developer Tools, Open Source, AI · YC page
Real-time audio & video SDKs, ready to launch 🚀
45 people · Bengaluru, KA, India · Video, API, Telecommunications · YC page
No-code platform for enterprise software companies
21 people · San Francisco, CA, USA · Developer Tools · YC page
Supercharge your mobile apps
9 people · Los Angeles, CA, USA · Developer Tools, Enterprise, AI · YC page
Observability platform for operations teams
8 people · New York City, NY, USA · Developer Tools, Data Engineering · YC page
Build better computer vision models by building better datasets
8 people · Brussels, Brussels, Belgium · Deep Learning, Developer Tools, Computer Vision · YC page
A faster and more collaborative alternative to Jira for remote teams
5 people · Oslo, Oslo, Norway · Developer Tools, Productivity, Team Collaboration, Remote Work · YC page
Open source continuous profiling software to debug performance issues
5 people · San Francisco, CA, USA · Developer Tools, Open Source, Kubernetes · YC page
AI Social Media Manager
4 people · Singapore, Singapore · Developer Tools, Design Tools, Social Media, AI · YC page
Multi-agent orchestration platform
40 people · San Francisco, CA, USA · Developer Tools, AI · YC page
Low latency API to run and deploy ML models
11 people · Austin, TX, USA · AIOps, Developer Tools, Machine Learning, AI · YC page
Synthetic data for better vision.
5 people · Toronto, ON, Canada · Machine Learning, Robotics, Computer Vision, Data Engineering · YC page
Continuous Documentation To End Documentation Rot
4 people · Bengaluru, KA, India · Documents, Developer Tools · YC page
AI-Powered Code Review
3 people · Stockholm, Stockholm County, Sweden · Developer Tools, AI · YC page
Nimbus reduces Datadog costs by more than 60% without Manual Effort
3 people · Seattle, WA, USA · Infrastructure, Operations, AI · YC page
The best database for app developers
3 people · Remote · Developer Tools, Web Development, Cloud Computing, Databases · YC page
2 people · San Francisco, CA, USA · Developer Tools, Gaming · YC page
Operating System for server-side apps
2 people · Vienna, Vienna, Austria · Developer Tools, Open Source · YC page
FAQ
How many developer tools companies are in YC Winter 2021 (W21)?+
40 launched companies in YC Winter 2021 carry a developer-tools or infrastructure tag in YC's directory (snapshot of 2026-10-20); 23 are active. Companies that have not launched publicly on YC's site yet are not counted.
What are the top tags in YC W21 dev tools?+
Developer Tools (34), AI (14), Open Source (11), API (4), Data Engineering (3). 11 of 40 are tagged open source.
Which YC W21 dev-tool companies are the largest?+
By team size on YC's directory: Encord, Gigs, Quicknode.
← Summer 2021Summer 2020 →All YC dev-tool companiesOpen-source YC companies
Source: Y Combinator's public company directory via the unofficial mirror yc-oss/api. DevHunt is not affiliated with Y Combinator.