Senior Product Engineer

Own features from Postgres schema to shipped UI across Next.js, NestJS, and GCP, and run the product side of what you build. AI-native, engineering first.

EngineeringToronto, hybridFull-time

Apply for this role

About the Role

This is an engineering role first. You'll design schemas, build APIs, ship UI, and operate production systems on GCP, and you'll be judged on the quality of what you ship. On top of that foundation you'll own the product side of your work too: you'll take a product question ("why did this model stop converting?"), turn it into a spec, build it end to end, and watch the metric move. A recent example: our market-prices system, where one engineer owns everything from the scraper data contract to the calibration report that tells us when a rival outbids us.

The role sits deliberately between product, design, and engineering. There's no separate PM writing your tickets. Our design system lives in code, so you'll make the design calls and ship polished UI without waiting for a handoff. And you'll build for two kinds of users: people and AI agents. Our trade-in flow already runs inside Claude through our MCP connector, and a growing share of our operations run as agent workflows the team writes as skills.

A note on AI-native: AI multiplies engineering skill, it doesn't replace it. You need the depth to review, correct, and own everything an agent writes, because you could have written it yourself. Vibe coding doesn't survive contact with a production pricing system.

What You'll Do

Own features end to end: spec, Postgres schema, NestJS and Cloud Functions APIs, Next.js UI, tests (Jest, Playwright), deployment, and the metric afterwards.
Build the systems behind pricing: market-data ingestion with dry-run validation, append-only observation datasets, and calibration reports ranked by competitor gap.
Ship customer-facing product across the quote, checkout, and merchant-embedded flows.
Design and implement APIs and integrations for merchant partners (Shopify, Magento, any custom API integration).
Do the product job for what you build, prioritizing directly with the CTO.
Extend our agent surface: write skills and plugins for the team, build MCP servers for internal tools, and improve the public Claude connector.
Automate operations with agents: alert triage, changelogs, reports, data checks. If you do something twice, you teach an agent to do it.

Apply if you

Have 5+ years of professional experience building and running production systems with TypeScript, Node.js, React/Next.js, and PostgreSQL. Real systems with real users, not demos or prototypes.
Have built and shipped production APIs and integrations, ideally on serverless GCP (AWS also valuable).
Care about data modeling: you understand why append-only tables, point-in-time correctness, and partitioning matter for data that will train models later.
Work AI-natively, and this is non-negotiable: agentic coding tools (Claude Code, Codex, or similar) are your daily driver, you write your own skills, plugins, and MCP servers, and you can defend every line an agent writes.
Have product sense: you can write a spec, scope an MVP, challenge a prioritization call, and own a metric.
Have design sensibility: you sweat UI details and can ship a polished interface from a design system without a handoff.

Even better if you have

Machine learning experience. The market-price dataset is built to be trained on, and you'd partner with the ML seat that owns pricing calibration.
LLM product features in production: tool use, structured outputs, evals.
Experience in e-commerce, fintech, or marketplaces.

Think this is you? We read every application.

Apply for this role

Why join SELLIT9?

Competitive salary in CAD (range depends on experience).

Meaningful equity: you're joining early, and your ownership reflects that.

3 weeks paid vacation: because work-life balance matters.

Hybrid work model: 3 days/week in our Downtown Toronto office + remote flexibility.

First access to traded-in inventory, priced at cost.

High-impact role in a fast-growing, venture-backed startup.

Founding-stage opportunity: play a key role in defining culture, processes, and product direction.

Career growth & mentorship from experienced founders (ex-Salesforce VP, ex-Scotiabank Head of Engineering).

Work alongside a compact, senior team where your work ships fast and matters.

The trade-in infrastructure for commerce

SELLIT9 turns used items into instant store credit or cash. We operate in Canada and the United States.

A lot of usable value sits unused in people's homes. Our pricing and logistics engines convert it, starting with electronics, into instant purchasing power, and every trade-in feeds a verified, graded supply pipeline. One loop: conversion and higher AOV for merchants, affordability for consumers, consistent supply for refurbishers.