Know what's going on
when it's going on
and inform people about it
and take actions with it.
Know what's going on
when it's going on
and inform people about it
and take actions with it.
Open Source ~ Self Hosted ~ Light Weight ~ Opinionated Tool for Observability, Communication and Automation.
Built for Speed & Performance
Powered by modern, lightweight, blazing-fast technologies for minimal overhead and maximum throughput
Bun
Blazing fast JavaScript runtime
Elysia
Fast & lightweight web framework
SvelteKit
Modern web application framework
Parquet
Columnar storage format
DuckDB
In-process analytics DB
& more
Postgres, Redis, and more essentials for scale
Why This Matters
Click to learn why this stack is perfect for observability
Start with Simple Logging
Every great observability journey begins with understanding what's happening in your application. Deltas gives you structured logging that's actually useful.
Four Log Levels, One Simple API
Whether you're debugging locally or monitoring production, use the right level for the right moment. Each log method accepts a message, optional data payload, and user ID for tracking.
Track What Matters with .fyi Events
Logs tell you what happened ~ .fyi events tell you what it means. Track user actions, business metrics and product analytics. All in one unified stream.
Beyond Traditional Logging
.fyi events are semantic markers for important moments in your application. Unlike raw logs, they're designed for:
User Journey Tracking
See the complete path from signup to conversion
Product Analytics
Understand which features drive engagement
Business Metrics
Track revenue, conversions, and KPIs in real-time
Unify Your Entire Stack
Your application doesn't exist in isolation. Connect webhooks from any service be it GitHub, Stripe, Shopify, auth providers, IoT devices into one unified event stream.
Instant Endpoints
Create webhook endpoints in seconds. Each endpoint gets a unique URL that automatically captures and stores incoming payloads.
Automatic Parsing
Deltas automatically parses JSON payloads, extracts headers, and stores everything in a queryable format. No manual parsing needed.
Trigger Actions
Route webhook events to workflows, send notifications, or trigger custom logic—all without writing integration code.
Works with Everything
And hundreds more. If it can send HTTP requests, it works with Deltas.
See Everything in One Place
Instead of checking multiple dashboards, view all your external events alongside your application logs and FYI events. Correlate a Stripe payment with a user signup, or a GitHub deployment with an error spike.
Beautiful Emails, Zero Hassle
Design stunning email templates visually, then send them programmatically. No more wrestling with inline styles, or email service APIs.
Visual Template Builder
Drag, drop, and design. Our visual editor makes it easy to create professional email templates without touching HTML. Add dynamic content with Jinja templating.
Live Preview
See exactly how your email looks across devices
Template Versioning
Track changes and roll back if needed
Jinja Templating
Loops, conditionals, filters—full template power
Automate Complex Workflows Visually
Build multi-step workflows with a visual node-based editor, then trigger them from your code. No Zapier subscriptions, no vendor lock-in—just powerful automation you control.
No-Code Workflow Builder
Connect actions like building blocks. Add conditions, loops, delays, and error handling—all visually. Perfect for complex business logic that changes frequently.
Pre-built Actions
Send emails, call APIs, query databases, trigger webhooks, and more
Custom Actions
Write your own actions in JavaScript or Python
Real-time Monitoring
See which step is running, what failed, and why
Retry & Recovery
Automatic retries with exponential backoff, or manual retry with one click