Full Stack Developer (permanent)

ScaleFast; Friauville; Hybrid; EUR 55,000 - 85,000; Full time

Benefits offered by this job

Leeto benefits

Fully remote policy

Job summary

ScaleFast is hiring a software engineer to join the Copilot team, building end-to-end features from database to UI. You’ll ship production-ready components, integrate telephony, CRM and data enrichment, and evolve the AI pipeline to support sales reps.

Expect collaboration with CTO and founders, strict code quality, and fast iteration in a fully remote French setup. You’ll contribute to a multi-faceted product stack (Next.js, Postgres, AI tooling) with an emphasis on production-readiness and

Qualifications

• At least 2 years of web development in production with Node.js on the server and SQL you write yourself (PostgreSQL preferred).
• You test what you ship and know why: unit tests on pure logic and end-to-end tests on critical paths.
• You have integrated third-party APIs and know their traps: lost webhooks, idempotency, secrets, pagination.
• You use coding assistants daily and review their output with the same rigor as your own code.
• Fluent French and written technical English; the interface is multilingual (FR, EN, ES) and docs are in English.

Responsibilities

• Design and ship complete Copilot features: data model and migrations, Express API, interface, tests and documentation, in the same PR.
• Integrate and harden connectors: telephony platforms, CRM, data enrichment, read-only banking and accounting.
• Evolve the AI pipeline: call transcription, Claude analysis, semantic search, real-time whisperer during calls, Copilot agent with citations.
• Run the platform in production: monitoring, backups, security, deployments.
• Contribute to scalefast.fr (Next.js + Sanity) and to the content machine that publishes to it.
• Leave a regression guard behind every fixed bug, and tested pure logic behind every feature.

Skills

Node.js

PostgreSQL

SQL

Unit tests

API integration

French fluency

English technical

Tools

Next.js

WebRTC

Telephony

LLM APIs

Python

Job description

Who we are

ScaleFast helps B2B software companies grow their sales. Our method combines artificial intelligence with sector expertise to spot the companies that have a need and book qualified meetings with their decision-makers. Our results are measurable: some of our clients have tripled their number of qualified prospects in 90 days.

What sets us apart from a classic agency: we built our own platform. Every call, every list, every meeting goes through an internal tool we develop ourselves, and that tool is what makes the difference in the field.

The role

You join Steven, CTO and co-founder, to build the Copilot: the internal application that runs ScaleFast. Quote simulator, profitability dashboard, telephony aggregation, in-house dialer, list and enrichment engine, finance cockpit, AI coaching for sales reps, content machine: everything lives in one product, used every day by the whole team.

You are not here to work through tickets. You take a feature end to end, from the Postgres table to the screen, ship it to production within the week, and watch what it changes for the sales reps who use it. Technical decisions are made by the two of us, on numbers measured in production, not on slides.

What you'll do

• Design and ship complete Copilot features: data model and migrations, Express API, interface, tests and documentation, in the same PR.
• Integrate and harden our connectors: telephony platforms (signed webhooks, safety-net polls, recording archival), CRM (Attio), data enrichment, read-only banking and accounting.
• Evolve the AI pipeline: call transcription, Claude analysis, semantic search (pgvector), real-time whisperer during calls, Copilot agent with mandatory citations.
• Run the platform in production: monitoring and cron registry, Discord alerts, backups, security (encrypted keys, CSP, personal data never in cleartext), Railway deployments.
• Contribute to scalefast.fr (Next.js + Sanity) and to the content machine that publishes to it.
• Leave a regression guard behind every fixed bug, and tested pure logic behind every feature.

Our stack

• Hosted on Railway (app, Postgres, website), Scaleway S3 for audio and backups, versioned migrations with node-pg-migrate.
• Multi-vendor telephony (Minari, Ringover, Allo, Skipcall) and an in-house dialer on Telnyx and Twilio: WebRTC softphone, live transcript, AI whisperer.
• AI: Anthropic Claude, OpenAI (transcription, embeddings, Realtime), ElevenLabs (training voice agents).
• Quality: node:test and fast-check, Playwright, GitHub Actions, Semgrep, Dependabot, green CI required, squash-merge, automatic deployment of main.
• AI-assisted development (Claude Code, Codex), framed by conventions written into the repository: definition of done, diff review, word budgets on documentation.

What we're looking for

• At least 2 years of web development in production, with Node.js on the server and SQL you write yourself (PostgreSQL preferred).
• You test what you ship and you know why: unit tests on pure logic, end-to-end tests on critical paths.
• You have integrated third-party APIs and know their traps: lost webhooks, idempotency, secrets, pagination.
• You use coding assistants daily and review what they produce with the same rigour as your own code.
• Fluent French and written technical English: the interface is trilingual (FR, EN, ES) and the technical documentation is in English.

Nice to have

• Next.js, WebRTC or telephony.
• LLM APIs, application security, Python.
• Experience in a small team where you were responsible for production.
• A product used every day by the people you work with: field feedback arrives the same day.
• A technical team of two to start, working directly with the CTO and the founders, with no approval chain.
• A written engineering culture: conventions in the repository, incidents documented with their cause and lesson, reversibility by default.
• Topics rarely found together in a team this size: real-time telephony, AI in production, financial data, calling regulation.
• An AI-first team, backed by ElevenLabs, where AI speeds up production without replacing judgment.

Details

• Permanent contract (CDI), full time, starting as soon as possible.
• Remote (France).
• Compensation: based on profile and experience.
• Probation period: as set by the applicable collective agreement.
• Fully remote policy.
• Employee benefits through Leeto, our works-council platform.