Yumb
AI-powered cold outreach SaaS with multi-provider LLM fallback, lead prospecting, and automated follow-up sequences.
Overview
Yumb is an automated cold outreach tool I built to handle lead discovery, prospect matching, and multi-step email campaigns. The platform combines scraping across job boards and directories, resume-to-stack TF-IDF matching, personalized copy generation, and direct delivery through Gmail OAuth2 with thread continuity. Billing runs on Paystack (currently in test mode).
Architecture & Implementation
The backend is written in Go 1.25 using Chi and PostgreSQL 16 connection pooling via pgxpool. When querying LLMs, an automatic cascading engine falls back from Anthropic to Groq to OpenRouter, with an offline template generator if all remote providers fail. Worker pools manage concurrency for batch drafts and follow-ups. Authentication supports Passkeys (WebAuthn), Google OAuth2, LinkedIn OIDC, and password logins with Argon2id and OTP. Deployed on Render with multi-stage Docker builds and continuous testing via GitHub Actions.
Key Features & Results
- ▪Designed a 4-tier LLM fallback chain (Anthropic → Groq → OpenRouter → offline templates) so message drafting never stops during provider downtime.
- ▪Draft Studio generates outreach across email, LinkedIn messages, Twitter DMs, and automated 3-step follow-up sequences.
- ▪Scrapes company and hiring leads from Adzuna, RemoteOK, Remotive, and OpenStreetMap, with contributor email discovery via GitHub and Hunter.io.
- ▪Resume matcher parses PDF and DOCX files, using TF-IDF to pair the candidate's strongest background against the target company's stack.
- ▪Separated draft generation into worker pools (3 workers for initial copy, 4 for follow-ups) with batches capped at 25 items.
- ▪Authentication system supports WebAuthn passkeys, Google OAuth2, LinkedIn OIDC, and password logins with Argon2id and email OTP.
- ▪Integrated Gmail OAuth2 for in-thread replies and tiered sending limits (40/hour, 500 to 2,000/day).
- ▪Background CRM worker tracks reply status, auto-closes finished sequences, and monitors daily send volume.
- ▪Integrated Paystack billing in test mode with webhook verification, and connected Sentry on both Go and React services.
- ▪Configured GitHub Actions CI running go vet, live PostgreSQL container tests with race detection, and frontend verification.