I came across a Threads post this week from @vaibhavsisinty listing some of the most useful APIs for developers. It stopped me mid-scroll because honestly — every single one on that list was something I wish I'd known about earlier.
So I went deeper. Tested some, dug into the docs, checked the pricing, and put together the full breakdown for you.
Here are seven APIs that will genuinely save you weeks of building from scratch.
1. Mapbox — Maps and Location Without the Google Tax
If you've ever tried adding maps to an app and gone straight to Google Maps, you know the pricing anxiety that follows. Every API call counting, every zoom adding up.
Mapbox is the alternative most developers don't know about until they've already paid Google's bill once.
You get maps, navigation, geocoding, and location intelligence — all through a clean API that works with any tech stack. The free tier is genuinely generous for early-stage projects and side work. The developer experience is excellent. And the customisation options are miles ahead of what Google Maps offers out of the box.
If you're building anything location-aware — delivery apps, logistics tools, store locators, travel products — start here before you start anywhere else.
Best for: Any app that needs maps, routing, or location features.
Free tier: Yes — usage-based pricing with a free monthly allowance.
Try it: mapbox.com
2. Resend — The Email API That Actually Works
Every developer has a story about transactional emails ending up in spam. The password reset that never arrives. The welcome email sitting in a junk folder. The invoice notification the customer never saw.
Resend fixes this.
It's an email API built specifically for developers — clean documentation, simple integration, and most importantly, emails that actually land in inboxes. Not promotions. Not spam. Inboxes.
The developer experience is the best in the category right now. You can send your first email in about ten minutes. It supports React Email for templating, which means you write your email templates in JSX and they render beautifully across every client.
If you're starting a new project and need transactional email — don't even look at anything else first. Start with Resend.
Best for: Transactional emails, password resets, notifications, welcome sequences.
Free tier: Yes — 3,000 emails per month free.
Try it: resend.com
3. Clerk — Authentication Done in Minutes, Not Weeks
Authentication is one of those things every app needs and nobody wants to build. Login, signup, password reset, session management, MFA, social logins — it's weeks of work done correctly, and a security nightmare done poorly.
Clerk handles all of it.
Drop it into your project, configure it once, and you have a complete auth system with a pre-built UI that doesn't look terrible. It works with Next.js, React, Node, and most modern frameworks out of the box.
The part that makes Clerk specifically stand out: the developer experience is genuinely thoughtful. The docs are clear, the components are customisable, and the user management dashboard is one of the best in the space. For solo developers and small teams who want to ship fast without cutting corners on security — this is the move.
Best for: Any app that needs user authentication, sessions, and user management.
Free tier: Yes — up to 10,000 monthly active users free.
Try it: clerk.com
4. Stream — Real-Time Chat and Feeds Without the Infrastructure Headache
Building real-time chat from scratch is one of the most underestimated engineering challenges. WebSockets, message history, read receipts, offline handling, scaling — it's a rabbit hole that can consume weeks of engineering time on infrastructure that isn't your core product.
Stream is the API that powers the chat and activity feeds in apps you already use. You get drop-in SDKs for React, React Native, iOS, and Android with pre-built UI components. Customise the look and feel, connect it to your backend, and you have production-grade real-time messaging running in a day.
The free tier covers most early-stage use cases. The scaling story is solid — Stream is built to handle millions of concurrent users, so you're not going to outgrow it as you grow.
Best for: Apps that need real-time chat, messaging, or activity feeds.
Free tier: Yes — up to 5 million messages per month free.
Try it: getstream.io
5. Cloudinary — Never Think About Images Again
Every app eventually has an image problem. Users upload files that are too large. You need to resize on the fly for different screen sizes. You want WebP for performance but the user uploaded a PNG. You need a CDN but don't want to set one up.
Cloudinary solves all of that with one API.
Upload an image once. Then transform it on demand through the URL — resize, crop, compress, convert format, add watermarks, apply filters. It all happens at the CDN edge so delivery is fast everywhere. The free tier gives you 25GB of storage and managed delivery, which is plenty for most projects getting started.
Cloudinary offers a free plan, Plus at $89/month, and Advanced at $224/month for teams that need more. But for most developers, the free tier gets you surprisingly far. Opal
Best for: Any app with user-uploaded images or video, e-commerce, media platforms.
Free tier: Yes — 25GB storage included.
Try it: cloudinary.com
6. AssemblyAI — Speech to Text That Actually Understands Context
Most speech-to-text APIs give you a wall of text with no punctuation and questionable accuracy on anything technical. AssemblyAI is different.
You get transcription, yes — but also summarisation, sentiment analysis, topic detection, and content moderation all from a single audio file. The accuracy on technical content, developer conversations, and domain-specific language is significantly better than most alternatives.
One API call. You get back not just a transcript but a structured understanding of what was said, who said it, what it was about, and how the speaker felt saying it. For anyone building voice products, meeting tools, podcast apps, or audio analytics — this is the one to know.
One heads up: in-region model pricing is increasing by 10% from July 1, 2026 — but you can maintain current pricing by adding "model_region": "global" to your API requests. Worth knowing before you ship anything that relies on it heavily. Geeky Gadgets
Best for: Voice apps, meeting transcription, podcast tools, audio analytics.
Free tier: Yes — $50 in free credits on signup.
Try it: assemblyai.com
7. Supabase — The One I'm Adding to the List
Supabase is an open source Firebase alternative that gives you a full backend in minutes — Postgres database, authentication, file storage, real-time subscriptions, and edge functions, all under one roof.
What makes it developer-friendly is how quickly you can go from zero to a working backend. Create a project, get your API keys, and you have a production-grade Postgres database with a REST API auto-generated from your schema. No setup, no infrastructure, no DevOps.
The free tier is generous enough to take a project from idea to early users without spending a cent. And because it's open source, you can self-host when you're ready to.
Best for: Full-stack developers who want a complete backend without the setup overhead.
Free tier: Yes — two free projects included.
Try it: supabase.com
🛠 Dev Tip of the Week
Before building any feature from scratch, spend five minutes searching for an API that already does it. Auth, email, maps, chat, media, speech — there's a well-maintained API for almost everything now. The math has changed: building it yourself is often slower, more expensive, and less reliable than using something battle-tested. Your job is to build what's unique to your product, not to reinvent infrastructure that already exists.
If you're already using one of these and have a strong opinion about it, hit reply. Always curious what developers are actually running in production.