Letterbook

AI-native customer support platform

4.0Score#168 of 999 agents#15 of 35 in Customer support agent

Why it ranks #168

Letterbook, an AI customer support agent from YC S23, ranks #168 of 999 AI agents and #15 of 35 in Customer support agent, with a score of 4.0 of 10. Data as of 3 Oct 2026.

The score adds four parts, each 0 to 10, by weight. Every point comes from public evidence. How scoring works ·

Proof 4 × 30% 1.2
Scale 2 × 30% 0.6
Momentum 5 × 25% 1.3
Autonomy 6 × 15% 0.9
= 4.0

Proof
Do customers use it? 30% of the score
4
Claims a customer count and work done at scale.
- +2
  A customer count
  “We grew our last product, Martin (an AI personal assistant), to 100,000 users.”
  Launch YC post · 15 Apr 2026
- +2
  Work done at scale
  “At one point, we'd get 50 customer support tickets every day, across email and help forms…”
  Launch YC post · 15 Apr 2026
Not found: revenue or growth (+4), named customers (+3), a customer result (+2)
Scale
Is there a real company behind it? 30% of the score
2
2 people, raised $2.0M.
- +1
  2 people on its YC page2 people
- +1
  Raised $2.0MThese Yale and Berkeley dropouts just raised $2 million to build an AI assistant that could rival OpenAI | VentureBeatSource · 30 Jan 2025
Momentum
Is it shipping and growing now? 25% of the score
5
Shows a recent launch and a new claim.
- +3
  Launched in the last 6 monthsLetterbook - AI Customer Support Built for StartupsLaunch YC post · 15 Apr 2026
- +2
  A new traction claim
  “We grew our last product, Martin (an AI personal assistant), to 100,000 users.”
  Launch YC post · 15 Apr 2026
Not found: open roles on YC (+2), funding news in the last year (+2), a batch in the last year (it is YC Summer 2023) (+1)
Autonomy
How much of the job does it do on its own? 15% of the score
6
Supervised agent: takes actions in other systems; a person approves key steps.
- +6
  Level 2 of 4: Supervised agentTakes actions in other systems; a person approves key steps.
What the model read
- Acts in other systems: 75% likely
- Finishes whole tasks: 47% likely
- Calls itself an agent: 6% likely
Level 2: Takes actions in other systems; a person approves key steps.

About Letterbook

Letterbook is the AI-native alternative to Zendesk, Freshdesk, Zohodesk, and Intercom. We help companies manage and resolve customer support tickets across email, in-app feedback, and website forms. Our AI will triage your tickets, write replies, and build your knowledge base.