Preston Li

I am a senior full‑stack engineer with over a decade building fast, safe, and auditable money‑movement systems across fintech, e‑commerce, insurance, and healthtech. I specialize in high‑volume card‑not‑present checkout, authorization routing, network tokens, and 3DS2/SCA.

At Square I owned authorization, 3DS2/SCA, and post‑auth flows, tuning services to keep p95 under 200ms and implementing network tokenization and targeted step‑ups to improve approval rates and dispute outcomes. I have repeatedly raised approval rates and reduced latency while keeping thorough reconciliation and auditability.

I design event‑driven microservices on AWS/EKS using Kafka/Kinesis, gRPC/HTTP/GraphQL, Postgres/DynamoDB/Redis, and ship infrastructure with Terraform and CI/CD — instrumented with OpenTelemetry, Prometheus/Grafana, Datadog, and ELK. I’ve delivered merchant dashboards, reconciliation tooling, and operational runbooks that cut Finance handoffs and MTTR.

I am pragmatic about reliability engineering — circuit breakers, brownouts, canary/blue‑green deployments, and feature flags — and I partner with security and compliance teams to enable tokenization, least‑privilege access, and auditable trails that satisfy finance and regulatory needs.