01treemap
Sector map
Every sector as a tile sized by company count. Filter to a batch like "Fall 2026" or to active companies only.
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~6,400 companies9 sectorscited answers
What are startups stirring up?
Explore Y Combinator startups by sector and by the customer problems they solve. Pick a sector, ask in plain English, and watch the companies each answer relies on collect in a grid.
Specimens · 01–06
The whole directory, filed by the problem it solves.
02basket
The basket
A sector as a wall of logos, narrowed by AI-suggested problem groups ("Scheduling", "Billing") or by name.
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03citations
Ringed citations
Answers are written only from the companies' own descriptions. The companies they cite get a crimson ring in the grid.
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04memory
Follow-ups that remember
Every company already discussed stays in context, so "tell me more about this one" just works.
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05web
From the web
Funding or news questions get a separate, clearly labelled web section with source links.
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06workbench
Profile, compare, note
Open a company profile, put two side by side, and keep notes on the ones worth a second look.
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Three ways to ask
One chat, three intents.
Ask about a sector
Question a sector, a problem group, a batch, or a hand-picked selection of companies. The answer cites who it relied on.
Ask about Healthcare companies…↑
Field notes
How an answer is grown.
Load the directory
Company data from the open-source yc-oss mirror goes into Postgres, with pgvector embeddings and AI-written problem groups per sector.
Choose a scope
A sector, a batch, a problem group, or companies you picked. The scope travels with every question in the session.
Answer from descriptions only
Retrieval finds the relevant companies and the model answers from their own words. A schema check keeps every citation pointing at a real company.
Reach past the data
When a question is about news or funding, a second call searches the web through OpenRouter and returns a labelled section with links.
Built with
Next.js 16React 19Postgres + pgvectorOpenRouterVercelVitestPlaywright
Not affiliated with Y Combinator. Whatstir is an independent project. Company data comes from yc-oss, an open-source mirror of the public YC directory.