Y Combinator S21
YC Summer 2021 developer tools companies
Web search rebuilt for LLMs
75 people · San Francisco, CA, USA · Developer Tools, Search, AI, APIs · YC page
AI-native on-call and incident response carefully crafted to help…
75 people · San Francisco, CA, USA · AIOps, Developer Tools, Security · YC page
One API to get clean data from any website for your AI agents at scale
70 people · Austin, TX, USA · Developer Tools, API, AI · YC page
Open Source Infrastructure for the Financial Internet
33 people · Paris, Île-de-France, France · Developer Tools, Fintech, Payments, Open Source · YC page
Plaid for Brazil: we allow developers to access users' financial data
31 people · São Paulo, SP, Brazil · Fintech, API · YC page
AI CAD Software for Civil Engineering
25 people · San Francisco, CA, USA · Machine Learning, Computer Vision, Design Tools, Infrastructure · YC page
Subscription infrastructure & paywall experimentation for mobile apps
25 people · New York City, NY, USA · Developer Tools, Payments, AI · YC page
Executable specifications in English for test automation
25 people · San Francisco, CA, USA · Developer Tools · YC page
The fastest way to ship airtight AI
24 people · San Francisco, CA, USA · AIOps, Developer Tools, Generative AI, Machine Learning · YC page
Sell anything
20 people · San Francisco, CA, USA · Developer Tools, Marketing, AI · YC page
The Work Number for LatAm
17 people · Mexico City, CDMX, Mexico · Payroll, API · YC page
Automated e2e screenshot testing without writing or maintaining tests
15 people · London, England, United Kingdom · Developer Tools, Hard Tech · YC page
AI SDET for mobile apps
15 people · San Francisco, CA, USA · Developer Tools, Generative AI, No-code, AI · YC page
Flexible Business Apps for Modern Teams
15 people · Dublin, County Dublin, Ireland · Developer Tools, No-code · YC page
Native user-facing SaaS integrations for your customers
13 people · Washington, DC, USA · Developer Tools · YC page
TURN STATIC DOCS INTO INSTANT ANSWERS
12 people · Bucharest, Bucharest, Romania · Developer Tools · YC page
Make all team work visible — people and AI agents
11 people · Remote, OR, USA · Developer Tools, Collaboration, AI, AI Assistant · YC page
Plan and review AI generated code
10 people · London, England, United Kingdom · Machine Learning, Open Source, AI · YC page
Pipekit scales data & CI pipelines for enterprises
9 people · Remote · Developer Tools, Open Source, Data Engineering, DevOps · YC page
Cloud and Container Security Platform
8 people · San Francisco, CA, USA · Cloud Workload Protection, DevSecOps, Identity, Security · YC page
Accelerate software development with WarpBuild's 10x faster CI infra.
8 people · San Francisco, CA, USA · Developer Tools, Generative AI, Productivity, DevOps · YC page
Google-level engineering productivity suite
6 people · San Francisco, CA, USA · Developer Tools · YC page
Business intelligence as code
6 people · Toronto, ON, Canada · Developer Tools, Analytics, Data Engineering, Data Visualization · YC page
The complete production quality platform. AI-powered E2E testing,…
5 people · Limerick, County Limerick, Ireland · Developer Tools, Open Source, DevOps · YC page
Web infra for AI agents
4 people · San Francisco, CA, USA · Developer Tools, AI · YC page
Measure and communicate engineering activity
3 people · Amsterdam, NH, Netherlands · Developer Tools · YC page
Open-source monitoring for machine learning models
2 people · London, England, United Kingdom · Developer Tools, Machine Learning, Open Source · YC page
Incredibly reliable background task queues and cron jobs
1 person · Austin, TX, USA · Developer Tools · YC page
The custom all-in-one OS for each company.
1 person · São Paulo, SP, Brazil · Developer Tools, HR Tech, AI, AI Assistant · YC page
Online University for Tech Professionals
San Francisco, CA, USA · AI-Enhanced Learning, Developer Tools, Education, Machine Learning · YC page
Build frictionless signup flows in minutes
10 people · A Coruña, GA, Spain · Developer Tools · YC page
Eliminate Cloud Waste. Attribute and Track Savings. Engage Engineers.
8 people · San Francisco, CA, USA · Developer Tools, FinOps, Workflow Automation, Cloud Computing · YC page
Reliable blockchain indexing & querying for web3 engineering teams.
5 people · San Francisco, CA, USA · Developer Tools, Crypto / Web3, Data Engineering · YC page
Authorization and access control as a service.
3 people · Los Angeles, CA, USA · Developer Tools, Open Source, API · YC page
Never code alone.
8 people · San Francisco, CA, USA · Developer Tools, Compliance, Security, AI · YC page
Your Customer Success Co-Pilot
5 people · San Francisco, CA, USA · Developer Tools, Customer Success · YC page
Observability for Data Engineering Teams
3 people · New York City, NY, USA · Machine Learning, Big Data, Data Engineering · YC page
Delightful components for iOS.
2 people · Berlin, Berlin, Germany · Developer Tools · YC page
Analytics for builders. Record and query billions of datapoints with…
1 person · New York City, NY, USA · Developer Tools, Analytics, Databases · YC page
FAQ
How many developer tools companies are in YC Summer 2021 (S21)?+
39 launched companies in YC Summer 2021 carry a developer-tools or infrastructure tag in YC's directory (snapshot of 2026-10-20); 30 are active. Companies that have not launched publicly on YC's site yet are not counted.
What are the top tags in YC S21 dev tools?+
Developer Tools (33), AI (12), Machine Learning (6), Open Source (6), API (4). 6 of 39 are tagged open source.
Which YC S21 dev-tool companies are the largest?+
By team size on YC's directory: Exa, Rootly, Anakin.
← Winter 2022Winter 2021 →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.