DEV Community: N3ST3D Labs

Building a Crypto-Native Fantasy Sports App on Solana — Web2 + Web3 Auth, USDC Prizes, and a Bracket System for the World Cup

N3ST3D Labs — Wed, 13 May 2026 00:18:13 +0000

How we built $BRACKETS — a FIFA World Cup 2026 fantasy league where players sign in with Google, Facebook, or a Solana wallet and compete for $BRACKETS and USDC prizes in 170+ countries.

Most fantasy sports platforms force you to choose — either build for crypto natives and lose casual users, or build for casual users and lock out the Web3 crowd entirely.
We refused to pick.

$BRACKETS is a FIFA World Cup 2026 fantasy league that works for everyone. Casual fans sign in with Google or Facebook and never touch a wallet. Crypto natives connect Phantom or Solflare and sign a message. Both play the same game, compete on the same leaderboard, and win the same USDC prizes — paid directly to their wallet regardless of how they signed up.
In this post I'll walk through:

Why we supported both Web2 and Web3 authentication in the same NextAuth session
How we unified Google OAuth, Facebook, and Solana wallet signatures into a single user model
The Solana wallet verification flow using verifySolanaSignature
How we structured USDC prize pools and KYC flows for winners
The bracket migration cron jobs and playoff logic
Building the Meteora DBC liquidity pool for the $BRACKETS token
Auth headaches with Brave browser, PKCE cookies, and ModSecurity WAF
What we'd do differently starting today

Stack: Next.js 15 App Router · Node.js/Express · MongoDB · Solana web3.js · NextAuth v5 · Jupiter + Meteora DBC · Ant Design · DigitalOcean

The auth architecture in one paragraph — give readers a taste before the full article:
The hardest part wasn't the blockchain — it was unifying three completely different identity systems into one session. Google and Facebook return an email and OAuth token. A Solana wallet returns a public key and a signed message. We unified both into a single MongoDB user document with a connector field — "Google", "Facebook", or "Wallet" — and a shared JWT session that carries the same role, username, and Solana address regardless of how the user authenticated. Wallet users can optionally link an email later. Email users can optionally link a wallet. One account, two doors in.

🚀 The Problem with Online PDF Tools

N3ST3D Labs — Sun, 03 May 2026 20:31:31 +0000

We’ve all been there. You need to convert a PDF to an image, but the "free" websites have limits:

"Only 3 files per day."

"File too large, please upgrade."

Privacy risks: You are uploading sensitive data to a random server.

As a developer, I knew there was a better way.

💡 The Solution: Local-First Processing
I built the PDF to Image Tool for freeapptools.co. The main goal was simple: The files should never leave the user's computer.

By using the power of the modern browser, we can handle the conversion locally. No servers mean no costs for me and total privacy for you.

🛠 How it Works (The Tech Stack)
To make this work smoothly, I used:

Next.js: For a fast, SEO-friendly frontend.

PDF.js: To render PDF pages onto a hidden HTML5 Canvas.

React Image Crop: To allow users to manually select and crop specific parts of their documents.

JSZip: To bundle multiple converted images into a single ZIP file for easy downloading.

✨ Key Features
Bulk Upload: Drop 10 PDFs at once, and it will process them in a single batch.

Manual Cropping: Perfect for extracting just a signature, a chart, or a specific paragraph.

Privacy Guaranteed: Since everything is JavaScript-based in the browser, your data is never stored or logged.

Zero Cost: No subscriptions or "premium" watermarks.

📈 Why this matters for Developers
If you are building tools for users, "Client-Side" is the way to go for 2026. It reduces your server costs to zero and builds massive trust with your users. People are becoming more aware of their data privacy—giving them a tool that doesn't "watch" them is a huge competitive advantage.

🔗 Try it out!
I’d love for you to test the tool and give me your feedback. What other "local-only" tools should I build next?

Check it out here: FreeAppTools - PDF to Image

Stop Fighting Image Formats: The Dev’s Guide to Stress-Free Conversion

N3ST3D Labs — Sun, 01 Mar 2026 16:28:48 +0000

We’ve all been there. You’re five minutes away from a production deploy, and you realize the "hero image" provided by the design team is a massive, unoptimized 5MB PNG. Or worse, you’re trying to upload a profile picture to a legacy system that only accepts JPEGs, but your screenshot is a WebP.

Handling image formats shouldn't feel like a chore. That’s why we built the Online Image Converter at Free App Tools. It’s a browser-based, privacy-first utility designed to get you back to coding faster.

Use Case: Optimizing for Core Web Vitals
If you’re a web developer, you know that WebP is the gold standard for web performance. It offers superior lossless and lossy compression compared to JPEG and PNG.

The Scenario:
You have a folder of high-res PNG screenshots for your documentation. If you ship them as-is, your page load speed (LCP) will tank.

The Fix:

Drag your PNGs into the Free App Tools Image Converter.

Select WEBP as your output format.

Hit convert.

In seconds, you’ve reduced your image payload by up to 30% without any visible loss in quality. Your users (and Google’s search bots) will thank you.

📐 Supported Formats
JPEG – Best for photos and gradients
PNG – Ideal for transparency and sharp graphics
WEBP – Modern format with excellent compression

✨ Features
✅ Convert JPEG, PNG, and WEBP images
✅ Optional image compression
✅ Removes unnecessary metadata (EXIF)

Better Tools, Better Workflow
We believe that the best tools are the ones that disappear into your workflow. Whether you're a designer needing a quick JPEG for a mockup or a dev optimizing a site for 2026 standards, we've got you covered.

Give it a spin here: https://freeapptools.co/tools/image-converter

Got feedback? We’re always looking to improve our suite of developer utilities. Drop a comment below!

Created @ N3ST3D LABS

https://freeapptools.co/tools/ethereum/ethereum-gas-fee-calculator

N3ST3D Labs — Sun, 22 Feb 2026 01:02:02 +0000

If you've ever been mid-transaction and had absolutely no idea what gas price to set, you're not alone. It's one of those things that trips up every Web3 developer at some point — especially when you're jumping between chains and each one has completely different fee dynamics.

We built a free browser-based tool to solve exactly this.

What It Does

The EVM Gas Fee Calculator gives you real-time gas prices for Ethereum, BNB Chain, Polygon, and other EVM-compatible networks. It fetches live fee data directly from public RPC endpoints every 30 seconds and shows you everything you need:

Current gas price in Gwei and Wei
EIP-1559 Max Fee Per Gas
Max Priority Fee (validator tip)
Estimated transaction cost in ETH

No wallet connection. No API key. Just open it and the data is already there.

👉 Try it free — freeapptools.co

Video Walkthrough

How to Use It

Select your chain from the dropdown — Ethereum, BNB Chain, Polygon, or whichever EVM network you're working on. The live gas prices load immediately.

Enter your gas limit. For a standard ETH transfer that's 21,000. For ERC-20 transfers use around 65,000. For smart contract interactions it varies — anywhere from 100,000 to 500,000 depending on what you're calling.

Hit Calculate and you get the estimated fee in ETH instantly. One click copies it to your clipboard.

EIP-1559 Support

A lot of calculators out there still only show legacy gas prices. This one gives you the full EIP-1559 breakdown — Base Fee, Max Fee, and Priority Fee — so you're working with the actual values your wallet submits on modern Ethereum transactions.

Multi-Chain

Switch between chains and the live data updates immediately. Useful when you're deciding whether to deploy on Ethereum or move to a cheaper L2. The difference in gas costs between Ethereum mainnet and Polygon can be dramatic — seeing it in real numbers makes the decision easier.

Stack Used

Built with Next.js, Ant Design, and ethers.js. Gas data is fetched using provider.getFeeData() from ethers.js connected to public RPC endpoints. All calculations happen client-side — no backend involved.

How to Convert Ether to Wei, Gwei, Finney & Szabo (Free Tool)

N3ST3D Labs — Sat, 21 Feb 2026 01:53:54 +0000

If you've been writing smart contracts for more than a week, you've already made the mistake of passing the wrong unit somewhere. You meant to send 1 ETH and accidentally sent 1 Wei. Or you hardcoded a Gwei value and your transaction fee calculation was off by a factor of a billion.

It happens to everyone. Ethereum's unit system is powerful but unforgiving.

What Our Tutorial :

Why Ethereum Units Are Confusing

Ethereum doesn't use decimals under the hood. Everything is an integer. When you write msg.value in Solidity or pass a value through ethers.js, you're always working in Wei — the smallest unit.

Here's the full breakdown:

1 Ether = 1,000,000,000,000,000,000 Wei
1 Ether = 1,000,000,000 Gwei
1 Ether = 1,000 Finney
1 Ether = 1,000,000 Szabo

Gwei is what you'll use most for gas prices. Wei is what Solidity actually works with. Finney and Szabo show up in older contracts and documentation.

The Tool

Instead of doing this math in your head or keeping a conversion table open in another tab, we built a free browser-based converter that handles all of it instantly.

👉 Ether Unit Converter — freeapptools.co

Type any value in any unit and everything else updates in real time. It also shows live gas prices for Ethereum, Binance Smart Chain, and Polygon, with EIP-1559 base fees and max fees included. All values are copy-ready with one click.

Practical Use Cases

When you're writing a Solidity payable function and need to set a minimum value in Wei, when you're debugging a transaction and need to quickly verify what a gas price in Gwei translates to in ETH, when you're building a dApp and need to display human-readable ETH values from raw Wei responses from the chain — this is the tool you reach for.

No Sign Up. No Ads. Just the Converter.

Everything runs in your browser. Nothing is sent to a server. It's completely free and always will be.

Built by N3st3d Labs — we make free tools for developers and crypto builders at freeapptools.co

If you find it useful, bookmark it. You'll need it again.

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