David Blass

Boston, MA · david@arktype.io · ssalbdivad.comgithub.com/ssalbdivad · linkedin.com/in/ssalbdivad · arktype.io

TypeScript engineer. I write the TypeScript types other libraries depend on- and lately, the agents that write the rest.

Numbers: a snapshot of 2026-10-13; npm figures cover 2026-09-13 to 2026-10-12; each links to its source.

Experience

Author, ArkType ecosystem2022–present

• ArkType: TypeScript's 1:1 validator, optimized from editor to runtime. Its type-level parser infers TS syntax from strings; at runtime the same definitions compile to JIT-friendly validation code. 9.05M npm downloads a month, 7.87K GitHub stars.
• ArkRegex: the first library to validate and infer regex from TypeScript's type system. 733K views on the launch post.
• Attest: granular type-level benchmarking and testing for TypeScript; deterministic instantiation counts let CI catch slow types. 427K npm downloads a month.
• ArkSchema: a set-theoretic type system with intersections, subtyping and union discrimination.

Co-creator, Standard Schema2024–present

• Designed, with the creators of Zod and Valibot, the interface that lets any TypeScript validation library plug into any framework; integrated by tRPC, TanStack, Hono, React Hook Form and more. The spec package has 551M npm downloads a month, mostly transitive installs.
• Co-authored Standard JSON Schema, so any validator can define tool inputs for AI agents and MCP.

Co-founder, Pullfrog2025–present

• Co-founded Pullfrog: an open-source platform running AI coding agents in GitHub Actions (1.3K stars). Agents review PRs, triage issues, fix CI, resolve merge conflicts and test UIs in a headless browser.
• Built the model-agnostic agent runtime: OpenCode, BYOK, MCP tools, GitHub App/OIDC auth, sandboxed CI.
• Built tooling to run and coordinate many parallel coding agents, used daily to develop Pullfrog.

TypeScript performance consultant2023–2025

• Found, minimized, benchmarked and drove a TypeScript compiler fix for O(3^N) instantiations in chained Zod- and tRPC-style types; the patch is by Mateusz Burzyński (TypeScript#61505). It shipped in TS 5.9: 2.0× faster checks on AnswerOverflow's tRPC dashboard (6.66s → 3.29s, 5 runs each), 2.1× on a tRPC monorepo I tested (one run), and 2.9× on Klarna's app (self-reported).
• viem: found 1.86s spent computing one type's variance in MUD's build; hand-annotated variance now ships in viem (mud#2956, viem#2557).
• Prisma: 45% less check time on the generated file we restructured (prisma/orm#27046). Mongoose 8.19: 36–67% fewer instantiations on its InferRawDocType benchmarks (mongoose#15588).
• Deep expertise in V8 JIT optimization, including runtime codegen for high-throughput validation.
• Clients included tRPC, Drizzle, Prisma, Convex, AWS Amplify, Speakeasy, Stately, wevm, Vanta and Cloudinary.

Founder, Redo Inc.2019–2021

• Led a team building a desktop app that generates UI tests from recorded user interactions.

SDET II, Amazon Alexa Devices2017–2019

• Built PyEcho, Amazon's standard test-automation framework for Alexa devices (Python, Android).

How I work with agents

I build Pullfrog by running many coding agents in parallel, every day, through Ntwine- a local tool I maintain. It grew out of Frizz, an earlier open-source tool, and keeps its design: every agent thread on one board, and a queue of the ones that need me. The rules I've added on top, for the agents and for me: size work by scope, never in days; report honest effect sizes; lead with what changed; preserve evidence.

Talks

• Effect Days 2024 · Discriminated Unions in TypeScript, Effect, and ArkType
• TypeScript Congress 2023 · ArkType: Bringing TypeScript to Runtime

Education

Tufts University, 2011–2015. Computer Science, Entrepreneurial Leadership, Philosophy.