Accelerator

Y Combinator

Y Combinator is the most influential startup accelerator in the world, founded in 2005 by Paul Graham, Jessica Livingston, Robert Tappan Morris, and Trevor Blackwell. Originally split between Cambridge, Massachusetts and Mountain View, California, YC consolidated in Silicon Valley and is now headquartered in San Francisco. YC runs a three-month program four times a year (winter, spring, summer, fall), each batch typically funding 250-300 early-stage startups. Its standard deal invests $500,000 in every company: $125,000 for 7% of the company on a post-money SAFE, plus $375,000 on an uncapped SAFE with a Most Favored Nation (MFN) provision. YC has funded more than 5,000 companies with a combined valuation exceeding $600 billion, including Airbnb, Stripe, Coinbase, DoorDash, Instacart, Dropbox, Reddit, Twitch, GitLab, and Ginkgo Bioworks. The firm is led by president and CEO Garry Tan, a General Partner and himself a YC alum. YC is sector-agnostic but heavily developer-tools, AI, fintech, B2B/SaaS, infrastructure, healthcare, and hard-tech oriented, and its alumni network of 6,000+ founders, plus Demo Day, Startup School, Work at a Startup, and Hacker News, form the connective tissue of the modern startup ecosystem.

839 portfolio companies 838 publish APIs here 14 properties
Venture CapitalAcceleratorSeedDeveloper ToolsArtificial IntelligenceFintechInfrastructureB2B SaaSNorth AmericaSan Francisco
Portfolio Strength across 293 profiled portfolio companies on the network
46 top-rated API companies 17 exemplar · 29 strong
138 agent-ready companies 31 agent-native · 107 agent-ready
Average quality of the book:
Composite thin 39.6
Agent-Readiness agent-aware 28.8

Firms are ranked by cumulative portfolio strength — how many highly-rated API companies they've backed, weighted by tier across composite quality and agent-readiness. The averages below are a secondary read on the typical company in the book.

Y Combinator has 839 portfolio companies tracked on the APIs.io network, of which 293 (35%) publish APIs indexed here. The remaining 545 are tracked as profiles without a published API on the network.

Its highest-rated API providers on the network are Stripe, Drchrono, Onesignal, Boom Ai, Optimizely.

Portfolio on the Network

Portfolio companies that publish APIs indexed on APIs.io, grouped by their API Evangelist rating. Exemplar and Strong are expanded by default.

Exemplar 17 Complete, well-documented, and agent-ready
Strong 29 Solid coverage with minor gaps
Developing 107 Usable, with meaningful gaps to close
Openrelay1 API54.2Eligible5 APIs54.1Onecli1 API54.0Mezmo7 APIs53.5Voygr1 API53.5Rightnow1 API53.1Trybloom1 API51.9Podium24 APIs51.8Gocardless1 API51.7Sitefire1 API51.7Hevn Inc1 API51.3Readme2 APIs51.3Twitch6 APIs51.2Replicas1 API50.8Amika1 API50.7Clever2 APIs50.6Definite1 API50.4Inth1 API50.4Speko1 API50.3Primer2 APIs50.2Skymerse1 API50.0Flock Safety1 API49.9Padlet1 API49.9Font Awesome1 API49.8Lucent1 API49.7Corelayer1 API49.4Sponge1 API49.3The Hog1 API49.3Front2 APIs49.2Rentahuman1 API48.9Agnost Ai1 API48.3Testerarmy1 API48.3Mireye1 API48.2Revnu2 APIs48.2Totalis1 API48.1Zerosettle1 API48.0Deepgram3 APIs47.6Lattice2 APIs47.6Sourcebot1 API47.5Brownie1 API47.0Interfaze1 API46.8Kugelaudio1 API46.8Coinbase5 APIs46.6Nex1 API46.6Confident Lims3 APIs46.4Scale Ai1 API46.3Smol Machines2 APIs46.3Codag1 API46.1Pagerduty1 API45.9Result3 APIs45.9Gojiberry Ai1 API45.8Razorpay1 API45.8Clawvisor1 API45.7Heroku1 API45.6Fixture1 API45.4Amboras1 API44.9Permutive11 APIs44.4Glue1 API44.3Osmaura2 APIs44.3Qomplement1 API44.3Segment4 APIs44.3Chamber1 API44.2Constellation Space1 API44.2Sfox3 APIs44.0Zeplin1 API44.0Agentphone1 API43.8Cognito1 API43.8Airbnb2 APIs43.6Scott Ai1 API43.5Characterquilt1 API43.4Dropbox2 APIs43.4Ardent1 API43.2Understudy Labs1 API43.2Uselemma1 API43.2Oximy1 API43.1Lob1 API42.7Quartzy1 API42.7Reddit2 APIs42.7Shortkit1 API42.7Terminal Use1 API42.7End Close1 API42.6Trellistech1 API42.6Sequence Markets1 API42.3Jinba2 APIs42.0Superlog1 API42.0Plivo1 API41.9Heap2 APIs41.7Eigenpal1 API41.6Karumi1 API41.5Mason6 APIs41.1Platzi1 API41.1Valgo1 API40.9Screenpipe1 API40.8Oddpool2 APIs40.5Submittable1 API40.5Chatfuel3 APIs40.4Shipbob1 API40.3Flip3 APIs40.2Caretta1 API40.1Healthsherpa1 API40.1Usenarrative1 API40.1One Degree1 API40.0Lightsprint1 API39.9Rigetti Computing1 API39.9Tempo1 API39.8Cratejoy2 APIs39.5Forum1 API39.5
Thin 84 Limited public surface area
Emerging 48 Early or largely undocumented
Minimal 8 Almost no public developer surface

Rest of Portfolio

1 further portfolio companies that don’t yet have a provider page on the network.

Y Combinator

Scroll for all 1

Properties

Portfolio

Where the firm publishes its investments

Team

Partners and investing staff

Content

Blog, podcast, newsletter, and research

Firm

The firm itself

Other

Everything else declared in apis.yml

Cohort brief

Auto-generated

The 728 portfolio companies with APIs in the catalog, backed by Y Combinator, scored on the Kin Score. Every figure below is computed from the catalog — nothing here is written.

Providers
728
of 838 on the roster
Mean Kin Score
21.9
-2.5 vs catalog 24.4
Mean Agent Readiness
12.3
-0.4 vs catalog 12.7
Spread
1.2–87.9
median 13.9 · σ 18.2
How the 728 split by band
Exemplar 17Strong 29Developing 107Thin 85Emerging 204Minimal 286
Facet averages, against the whole catalog
FacetThis cohortCatalogDifferenceScored
Developer Ergonomics 23.3 23.8 -0.5 728
Discoverability 60.5 61.5 -1 728
Access Clarity 25.5 27.2 -1.7 728
Contract Governance 4.5 6.6 -2.1 728
Operational Transparency 11.4 14.4 -3 728
Contract Quality 15.7 20.4 -4.7 728

A facet is averaged over the members that carry it, not over the whole cohort — the “Scored” column is that count. Averaging an absent facet as zero would score our own coverage gaps as the providers’ posture.

What this cohort publishes
ArtifactThis cohortCatalogDifference
MCP server (any) 17% 11% +6
MCP server (first-party) 22% 13% +9
Agent Skills 0% 0% 0
OAuth scopes 11% 12% -1
Security 98% 96% +2
Arazzo workflows 4% 2% +2
Governance rules 6% 13% -7

mcp_pct counts any mcp/ artifact including ones API Evangelist derived from the provider OpenAPI; mcp_first_party_pct counts only servers the provider publishes. Prefer the latter.

Top by Kin Score
  1. 1 Stripe 87.9
  2. 2 drchrono 81.8
  3. 3 OneSignal 80
  4. 4 Boom Ai 79.9
  5. 5 Optimizely 78
  6. 6 Mux 77.7
  7. 7 Drippay 76.1
  8. 8 Doordash 75.8
  9. 9 GitLab 72
  10. 10 Algolia 71.5
Top by Agent Readiness
  1. 1 OneSignal 75.4
  2. 2 Primitive 75.2
  3. 3 Agentcard 68.3
  4. 4 Allowance 66.9
  5. 5 Drippay 66.1
  6. 6 Boom Ai 65.8
  7. 7 The Hog 65.5
  8. 8 Zapier 65.1
  9. 9 Resolve 64.2
  10. 10 Optimizely 62.5
This roster declares 838 members; 821 resolve to a provider in the catalog and 728 carry a score (89%). The figures above describe the scored members only.Generated from the catalog build of 22 September 2026, across 27674 providers, using the same computation served by the APIs.io cohort API. Briefs are published for rosters of 5 or more scored providers; below that a distribution is not meaningful.

Source (apis.yml)

apis.yml Raw ↑
aid: y-combinator
name: Y Combinator
description: >-
  Y Combinator is the most influential startup accelerator in the world, founded
  in 2005 by Paul Graham, Jessica Livingston, Robert Tappan Morris, and Trevor
  Blackwell. Originally split between Cambridge, Massachusetts and Mountain View,
  California, YC consolidated in Silicon Valley and is now headquartered in San
  Francisco. YC runs a three-month program four times a year (winter, spring,
  summer, fall), each batch typically funding 250-300 early-stage startups. Its
  standard deal invests $500,000 in every company: $125,000 for 7% of the company
  on a post-money SAFE, plus $375,000 on an uncapped SAFE with a Most Favored
  Nation (MFN) provision. YC has funded more than 5,000 companies with a combined
  valuation exceeding $600 billion, including Airbnb, Stripe, Coinbase, DoorDash,
  Instacart, Dropbox, Reddit, Twitch, GitLab, and Ginkgo Bioworks. The firm is
  led by president and CEO Garry Tan, a General Partner and himself a YC alum. YC
  is sector-agnostic but heavily developer-tools, AI, fintech, B2B/SaaS,
  infrastructure, healthcare, and hard-tech oriented, and its alumni network of
  6,000+ founders, plus Demo Day, Startup School, Work at a Startup, and Hacker
  News, form the connective tissue of the modern startup ecosystem.
x-type: venture-capital
x-category: Accelerator
deliveryModel:
  model: unknown
  open_source: false
  commercial: false
  callable_host: false
  label: Delivery model not determined — needs a product licence on record
  confidence: low
  source:
  - none
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source: []
  generated: '2026-07-22'
  method: derived
image: https://www.ycombinator.com/apple-touch-icon.png
created: '2026-07-17'
modified: '2026-07-17'
specificationVersion: '0.23'
tags:
  - Venture Capital
  - Accelerator
  - Seed
  - Developer Tools
  - Artificial Intelligence
  - Fintech
  - Infrastructure
  - B2B SaaS
  - North America
  - San Francisco
apis: []
common:
  - type: Website
    url: https://www.ycombinator.com
  - type: Portfolio
    url: https://www.ycombinator.com/companies
  - type: Portfolio
    url: portfolio/y-combinator-portfolio.yml
  - type: Team
    url: https://www.ycombinator.com/people
  - type: Team
    url: team/y-combinator-team.yml
  - type: InvestmentThesis
    url: https://www.ycombinator.com/about
  - type: Blog
    url: https://www.ycombinator.com/blog
  - type: Pitch
    url: https://www.ycombinator.com/apply
  - type: Jobs
    url: https://www.workatastartup.com
  - type: Crunchbase
    url: https://www.crunchbase.com/organization/y-combinator
  - type: LinkedIn
    url: https://www.linkedin.com/school/y-combinator/
  - type: Twitter
    url: https://twitter.com/ycombinator
  - type: GitHubOrganization
    url: https://github.com/ycombinator
  - type: Contact
    url: https://www.ycombinator.com/contact
  - type: Features
    data:
      - 'Model: Accelerator (3-month program, 4 batches per year)'
      - 'Stage: Pre-seed, Seed'
      - 'Typical check: $500,000 standard deal ($125K for 7% post-money SAFE + $375K uncapped SAFE with MFN)'
      - 'Batch size: 250-300 startups per batch'
      - 'Sectors: developer tools, AI, fintech, B2B SaaS, infrastructure, healthcare, hard tech (sector-agnostic)'
      - 'Geography: primarily North America; global applicants'
      - 'Companies funded: 5,000+ (combined valuation $600B+)'
      - 'Founded: 2005'
      - 'HQ: San Francisco, CA'
    sources:
      - https://www.ycombinator.com/about
      - https://www.ycombinator.com/deal
      - https://en.wikipedia.org/wiki/Y_Combinator
    updated: '2026-07-17'
maintainers:
  - FN: Kin Lane
    email: kin@apievangelist.com
    url: https://apievangelist.com
  - FN: APIs.json
    url: http://apisjson.org
  - FN: Y Combinator
    url: https://www.ycombinator.com

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