Skip to content
YC Root AccessYC Root Access

The Q/A Layer for the AI Coding Era

In this episode of Founder Firesides, YC Managing Partner Harj Taggar talks to Weiwei Wu and Jeff An, co-founders of Momentic (W24), who just raised a $15M Series A. Momentic is the verification layer for software — an AI-powered testing platform that impersonates end users to catch bugs before they ship. Powering companies like Notion, Quora, and Built with over a million test runs a day, they discuss why the explosion of AI-generated code makes testing more critical than ever and their vision for a future where engineers write specs, not code. https://momentic.ai Apply to Y Combinator: https://www.ycombinator.com/apply Work at a startup: https://www.ycombinator.com/jobs

Harj TaggarhostWeiwei WuguestJeff Anguest
Mar 22, 202633mWatch on YouTube ↗

At a glance

WHAT IT’S REALLY ABOUT

Momentic positions functional testing as verification layer for AI coding

  1. Momentic provides an AI-driven functional testing platform that impersonates real users in a browser to ensure critical user flows don’t break, processing over a million test runs per day for customers like Notion and Quora.
  2. The founders argue that AI code generation is exploding output while shifting the bottleneck to verification, making independent validation more important than ever even as code quality improves.
  3. Momentic integrates into the developer loop (via MCP) so coding agents like Cursor/Claude Code can write and run Momentic tests during development, not just in CI before merge.
  4. They promote “truth-driven/spec-driven development,” where plain-English specs and success criteria become the durable source of truth and tests continuously maintain that truth as products evolve.
  5. The discussion also covers company-building lessons—raising a $50M Series A to scale go-to-market and engineering, hiring for adaptability and product intuition, and building a culture of radical candor on a 13-person team.

IDEAS WORTH REMEMBERING

5 ideas

AI coding shifts the bottleneck from writing code to verifying behavior.

As code output scales (Cursor/Claude Code/Codex), teams still need a reliable way to confirm changes work in production-like conditions; Momentic positions itself as the high-leverage constraint remover.

Independent verification matters because agents can be confidently wrong.

The founders emphasize you can’t rely on the same coding agent to self-certify correctness; a third-party “source of truth” is needed to protect SLAs and prevent regressions reaching customers.

Functional tests should mirror user journeys, not just code structure.

Momentic focuses on end-user flows (clicking through the app, validating outcomes) to catch issues linters and code review can’t, especially for rich UIs like editors, drag-and-drop, and canvases.

Developer-loop testing becomes a first-class tool call for agents.

Via MCP, coding agents can invoke Momentic to run real browser verification while building features, tightening feedback cycles beyond traditional pre-merge QA.

Maintainability is the core differentiation versus generating Playwright/Selenium scripts.

They argue raw generated test code becomes an unmanageable pile (tens of thousands of lines) that breaks with UI changes, whereas Momentic encapsulates and auto-maintains the “source of truth” over time.

WORDS WORTH SAVING

5 quotes

I would be disappointed in, you know, three to six months I’m still reviewing TypeScript or React code.

Jeff An

I can’t really trust Claude Code or Cursor to tell me themselves. You know, I need a third… external source of truth for verifying that.

Weiwei Wu

Momentic tests must pass before one of Notion’s engineers can merge their PR.

Weiwei Wu

Your code is just an implementation of that source of truth.

Weiwei Wu

We will win and destroy them all. Like, it… is inevitable.

Weiwei Wu

Functional testing as “verification layer”AI codegen increasing verification bottlenecksLinters vs code review vs end-to-end validationMCP integrations with Cursor/Claude CodeDebuggability, speed, and flakiness reduction vs SeleniumTruth-driven/spec-driven developmentEnterprise adoption and ROI (hours saved, SEVs prevented)

High quality AI-generated summary created from speaker-labeled transcript.

Get more out of YouTube videos.

High quality summaries for YouTube videos. Accurate transcripts to search & find moments. Powered by ChatGPT & Claude AI.

Add to Chrome