DEV Community: dayu2333-jinyul

5 Free Financial Calculators I Built That I Actually Use Every Month

dayu2333-jinyul — Fri, 12 Jun 2026 00:30:02 +0000

I built FinCalc AI after realizing I was maintaining the same Excel spreadsheets for years.

Mortgage Calculator

Most online calculators give you a monthly payment and call it done. This one shows the full amortization schedule. Bi-weekly payments save 4-5 years and ~$65K on a $400K mortgage at 6.5%.

Compound Interest Calculator

$500/month at 7% for 30 years = ~$610K. Wait 5 years to start = only ~$440K. That delay costs $170K.

Retirement Calculator

Monte Carlo simulation with 1000 random scenarios. The 4% rule has a ~5% failure rate over 30 years.

ROI Calculator

For evaluating side projects. Forces you to value your time at a real hourly rate.

Debt Payoff Calculator

Snowball vs avalanche comparison. Avalanche is mathematically optimal, snowball works better psychologically.

→ All free at financalcai.com. No signup, no email, works on mobile.

I Built an AI Logo Generator — Here is What Actually Works vs What Does not

dayu2333-jinyul — Fri, 12 Jun 2026 00:29:30 +0000

I built AI Logo Generator because I wanted something that produced logos people would actually use, not just marvel at for 30 seconds and discard.

What works: style-constrained generation

The biggest problem with AI logo generators is they give you an image, not a logo. A logo needs to work at 32×32 (favicon), 200×200 (social avatar), and on a white background (print).

My approach:

Built on a Stable Diffusion pipeline with post-processing
Color palette extraction + simplification (max 3 colors)
Background removal as a required step
SVG conversion via potrace for the best outputs

The constraint most people miss: a good logo is a good silhouette first.

What sort of works: style selection

Giving users 8-10 style presets (minimalist, geometric, mascot, lettermark) dramatically improves output quality vs free-form prompting.

What does not work: one-shot generation

Almost zero AI logos come out perfect on the first generation. Useful ones come from iteration — generate 4 variations, pick the best, tweak colors, regenerate.

What I would tell someone building this

Focus on post-generation editing, not the image model. Everyone has access to the same AI models. The differentiation is how easy you make it to go from "cool AI image" to "actual usable logo."

→ aielogo.com — free, no signup needed for first 5 logos

I Built a Body Health Calculator Suite — BMI Made Me Do It

dayu2333-jinyul — Fri, 12 Jun 2026 00:29:16 +0000

BMI is a terrible metric. It was invented in the 1830s by a Belgian mathematician studying population averages, not individual health. It does not distinguish between muscle and fat and labels most athletes as "overweight."

So I built BodyCalc Tool — calculators that actually tell you something useful.

Body Fat Calculator

Uses the US Navy method (neck + waist + height for men, + hips for women). Validated against DEXA in multiple studies. Measurable at home with a $2 tape measure — no fancy equipment needed.

TDEE Calculator

Total Daily Energy Expenditure using Mifflin-St Jeor, with activity multipliers from sedentary to athlete. The activity multiplier is where most calculators get sloppy — I added concrete examples: "Moderate = you break a sweat, can talk. Example: 30 min jog at 6mph."

Waist-to-Hip Ratio

A better cardiovascular risk predictor than BMI. Ratio above 0.90 (men) or 0.85 (women) correlates with higher heart disease risk even at "normal" BMI. Most people have never measured this.

Ideal Weight + Protein Calculators

Ideal weight uses four formulas (Robinson, Miller, Devine, Hamwi) to show a realistic range instead of one magic number. Protein calculator uses the research-backed 0.8-2.2g/kg range based on activity level and goal.

What I learned

People want context, not numbers. A raw body fat percentage means nothing without knowing what is healthy for your age and gender.
Imperial + metric is non-negotiable. Half my users are American (lbs/inches), half international (kg/cm).
Privacy matters for health data. All calculations happen in the browser. Nothing stored server-side.

→ bodycalctool.com — all calculators free, no signup

What I Learned Building an AI Resume Optimizer — And What Recruiters Actually Told Me

dayu2333-jinyul — Fri, 12 Jun 2026 00:28:58 +0000

I built Resume AI Optimizer because I was job hunting and tired of sending the same resume to every posting.

But after building it and talking to actual recruiters, I learned a few things that surprised me.

The obvious part: ATS keyword matching

Most resume "optimizers" just stuff keywords from the job description into your resume. This technically works for getting past ATS filters, but recruiters can spot keyword-stuffed resumes instantly.

The approach I landed on:

Extract required skills + keywords from the job description
For each bullet point, check if it can naturally incorporate a missing keyword
Rewrite only when the keyword fits the context — never force it
Flag skills you genuinely don not have — do not lie, recruiters will catch it

Action verbs matter more than keywords

I ran 50 real job descriptions through the tool and showed samples to three recruiters. Their feedback was consistent: action verbs carry more weight than keyword density.

"Led a team of 5 engineers" hits harder than "Responsible for leading a team." Both contain "lead" but one sounds like a leader and the other sounds like middle management.

The tool has a heavy bias toward active voice and strong verbs. It will rewrite "Was responsible for managing the Q3 budget" → "Managed $200K Q3 budget, delivered 8% under projection."

Format matters more than you think

Recruiters spend an average of 6-7 seconds on first-pass resume screening. If your formatting is broken, they move on before even reading.

The tool checks: consistent date formatting, parallel bullet structure, no orphan words, correct section ordering.

What is still hard

Honest take: the tool works best for mid-level tech roles — software engineers, product managers, data analysts. For creative roles, the portfolio matters more than the resume. For executive roles, you need a human resume writer.

→ resumeaiopt.com — paste a job description, paste your resume, get an optimized version in ~10 seconds. Free tier gives you 3 optimizations.

I Built a Free AI Grammar Checker That Runs Entirely in the Browser

dayu2333-jinyul — Fri, 12 Jun 2026 00:28:44 +0000

I built AI Grammar Checker because I was tired of copy-pasting my writing between five different tools — Grammarly for grammar, Hemingway for readability, some word counter for stats.

What it does

Paste English text, hit check, and get back:

Sentence-by-sentence grammar corrections with explanations
Style polish — passive voice, weak adverbs, wordy phrases flagged
Flesch readability score so you know if your text is actually readable
Hemingway-style highlights — hard sentences, very hard sentences, adverb count
CEFR level (A1–C2) for non-native speakers
Tone detection — formal, casual, neutral

All client-side except the AI check call. No server stores your text.

The stack

HTML + vanilla JS + CSS
↓
DeepSeek API (OpenAI-compatible, $0.27/million tokens)
↓
Result rendered directly in the DOM

No React. No Next.js. No build step. Just app.js, style.css, and index.html.

Why DeepSeek over OpenAI

Cost. DeepSeek is roughly 1/10th the price of GPT-4o for comparable grammar quality. At free tier usage levels, my API bill is under $2/month.
Quality. Tested on a 50-sample set — DeepSeek caught 91% of errors vs GPT-4os 93%. The 2% gap is not worth 10x the cost.
No content moderation false positives. OpenAI sometimes flags academic writing about medical or legal topics. DeepSeek just checks grammar.

What Id do differently

Offline mode. Hemingway stats are local. Grammar needs the API. Want to bundle a small on-device model via WebLLM.
Better mobile UX. Works on mobile but text area + results layout is not great on narrow screens.
API key flow. Users bring their own DeepSeek key (5M free tokens for new users). Considering a shared-key free tier.

→ grammaraicheck.com — completely free, no signup.

Also: Best AI Grammar Checkers 2026 comparison.

Complete Arms of God Strategy Guide — Tips, Mechanics & Hidden Features

dayu2333-jinyul — Tue, 09 Jun 2026 14:16:29 +0000

How I Built a Fast-Loading Game Guide Site for Arms of God (And What I Learned About Roguelike Depth)

Been playing Arms of God for about 3 weeks now and honestly, this game has no business being this deep. You pick up these divine weapons, each with completely different move sets, and suddenly you're theory-crafting builds at 2am.

So I did what any sleep-deprived dev would do — built a guide site.

The technical side was actually interesting because roguelike data is messy. Weapon synergies aren't linear, blessings stack in weird ways, and the community keeps discovering new tech every week. Static pages wouldn't cut it.

I ended up structuring everything as modular content blocks:

Weapon data lives in JSON with relational tags for synergy mapping
Build guides use a custom MDX setup so I can embed interactive weapon comparison tables
Image optimization pipeline keeps load times under 1.5s (critical when someone's mid-run checking a guide)

The Arms of God content was way more nuanced than I expected — things like the Gauntlet's timing windows varying by 3-4 frames depending on which blessing you've stacked, or how the Spear's divine judgment proc actually scales with movement speed not attack speed (still waiting for that to get patched tbh).

Built the whole thing on Astro with minimal JS. Lighthouse scores are 98+ across the board and it stays snappy even with 40+ embedded gameplay clips per page. If you want to see how it turned out, I put together a quick overview of the Arms of God structure and the specific weapon guides that took the most research.

What roguelike systems have you found surprisingly hard to document properly? The RNG seed mechanics always trip me up.

Complete Deep Crafter Strategy Guide — Tips, Mechanics & Hidden Features

dayu2333-jinyul — Tue, 09 Jun 2026 14:15:27 +0000

How I Built a Crafting Tree Visualizer for Deep Crafter (And Why You Might Want One)

I've been absolutely sucked into Deep Crafter lately — the pressure management alone is brutal enough to keep me up at night, but the crafting system? That's where things get spicy.

For those who haven't drowned yet, Deep Crafter is a deep-sea survival game where you're building underwater bases while managing oxygen, pressure, and increasingly complex material requirements. The crafting chain for something like a reinforced titanium hull section goes deep (pun intended), and I kept losing track of intermediates.

So I did what any sleep-deprived dev would do — I built a visualization tool.

What the site actually does

The crafting tree visualizer I put together at deepcraftercrafting.com breaks down every recipe into a collapsible dependency graph. Here's what I focused on:

Pressure-tier filtering — materials behave differently at 200m vs 800m, and the crafting requirements shift accordingly. The tool lets you toggle depth ranges so you're not staring at irrelevant recipes
Intermediate tracking — some components (looking at you, crystalline alloy plates) need three sub-components that each need two sub-components themselves. The visualizer highlights bottlenecks
Base module optimization — if you're building multiple modules, the tool calculates shared intermediates so you're not over-farming

The trickiest part was actually the data structure. Deep Crafter's recipe system isn't purely tree-based — some items have circular dependencies where you need a basic version of a module to craft the advanced version, which then gets consumed. Lot of edge cases to handle there.

Why this matters for survival crafters

Most crafting games throw a recipe book at you and call it a day. Deep Crafter's depth-pressure system adds genuine complexity that a flat list can't capture well. I've noticed the community figuring out workarounds the hard way — spending hours farming materials that could've been optimized with a bit of planning.

The site's been live for about a month and the feedback loop has been wild. People keep submitting edge-case recipes I missed, and I've had to refactor the graph rendering twice already.

If you're playing Deep Crafter, what's the crafting chain that keeps tripping you up? I'm still struggling to optimize the sonar relay components efficiently.

Complete Killer Bean Strategy Guide — Tips, Mechanics & Hidden Features

dayu2333-jinyul — Tue, 09 Jun 2026 14:14:24 +0000

I've been working on a fan site for Killer Bean lately and figured I'd share some of the more interesting implementation details, especially if you're building game hubs or wiki-style sites.

The biggest challenge was rendering firearm stats in a way that actually helps players compare loadouts. Most shooter wikis just dump numbers into tables, but Killer Bean's weapon pool has weird modifiers — some guns have "bean-seeking bullet physics" that aren't reflected in base DPS values. So I ended up building a quick data layer that pulls from in-game testing data spreadsheets and renders them as visual stat bars with conditional tooltips explaining the hidden mechanics.

For the mission guides, I ditched the traditional walkthrough format and went with a decision-tree component. Each boss fight section dynamically loads tips based on which weapon loadout you clicked earlier, since strategies diverge hard depending on whether you're running the Dual Wield Deagles or the Explosive Burrito Launcher. The state management for that got messier than expected — definitely underestimated how many branching paths there are.

A few things that worked surprisingly well:

SVG bean sprites for the weapon icons. Way lighter than PNG spritesheets when you're rendering 40+ guns on a single page, and they scale perfectly on mobile without looking blurry.
Client-side search with fuse.js for the enemy database. Players wanted to quickly look up weak points mid-mission, so every millisecond counts. The fuzzy matching handles typos like "clmbot" instead of "climbot" which happens more than you'd think.
Lazy loading the gameplay GIFs. Some of those combo demonstrations are like 8MB apiece and were tanking the LCP score.

The whole thing's statically generated (Next.js) and hosted on a $5 VPS. I wrote up a more detailed breakdown over at [my blog URL] if anyone wants to see the actual component code and data schema — happy to share the repo too.

The localization part was actually the biggest headache. Extracting all the item descriptions and quips from the game files into a workable translation pipeline took way longer than the frontend work. If anyone's tackled game data extraction for fan projects, I'd love to hear how you approached the parsing logic — still feels hacky on my end.

Complete Gothic 1 Remake Strategy Guide — Tips, Mechanics & Hidden Features

dayu2333-jinyul — Tue, 09 Jun 2026 14:13:22 +0000

So I've been slowly rebuilding my Gothic 1 Remake guide site, and honestly the most interesting part wasn't the content — it was figuring out how to present the game's systems without overwhelming people. Gothic's combat isn't exactly intuitive for newcomers, and if you came from Skyrim or Witcher 3, the learning curve probably slapped you in the face.

Here's what I ended up focusing on from a technical/content standpoint:

The combat timing visualizer — Instead of just writing "press left then right to combo," I built these little animated sequences showing the actual input windows. Gothic's melee is all about rhythmic timing, not button mashing. Hardest part was syncing the animations to the correct frame data from the original game (the remake kept the same timing, thankfully).

Faction progression trees — The three factions (Old Camp, New Camp, Swamp Camp) have completely different quest chains and gear access. Built this as an interactive flowchart so you can see at a glance what locks you out of what. The Swamp Camp route is still the most underrated path btw — people sleep on those early game weed profits.

Enemy behavior patterns — Every creature type has specific aggro ranges and attack tells. I mapped them out using data tables since writing it out in paragraphs was just making things harder to parse. Scavengers circling before striking, wolves retreating at low health, shadowbeasts being absolute nightmares — it's all documented with actual trigger conditions.

Anyway, if anyone's working on similar game guide projects, I'd be curious — how do you handle mobile responsiveness for complex data tables? That's been my biggest pain point lately. Got most of the combat stuff sorted over at gothic-remake-strats if you want to see what I mean, but the tables are still kind of a mess on smaller screens.

Complete Hearts of Iron IV Strategy Guide — Tips, Mechanics & Hidden Features

dayu2333-jinyul — Tue, 09 Jun 2026 14:12:21 +0000

I've been building out a small strategy guide site as a side project, and recently spent way too much time dissecting HOI4's combat width mechanics. Thought I'd share what I learned since the game does a terrible job explaining this stuff.

The problem: most players just throw divisions at the front line and wonder why they're losing with 3x the factories.

Here's what actually matters under the hood:

Combat width meta shifted hard after No Step Back — the old 20/40 width templates aren't optimal anymore. Plains are 90 width, forests 84, mountains 75. You want divisions that divide cleanly into those numbers to avoid stacking penalties
Coordination stat is slept on — it determines how much your divisions focus fire instead of spreading damage. High coordination + signal companies = enemy divisions get deleted before reinforcements can cycle in
Air superiority applies a defense penalty to enemy units (up to -35% at max), but the tooltip just says "air support" like that means something

I put together a full breakdown of combat width calculators and terrain modifiers if anyone wants the raw numbers. The site also covers naval invasion templates and spy network optimization because honestly the wiki is outdated on half this stuff.

Building this taught me that HOI4's real game is spreadsheet optimization disguised as a map painter — which is probably why I've sunk 800 hours into it and still feel like a noob sometimes.

What's the one mechanic you wish Paradox would actually explain properly in the tutorial? For me it's still naval strike targeting priority.

Complete Euro Truck Simulator 2 Strategy Guide — Tips, Mechanics & Hidden Features

dayu2333-jinyul — Tue, 09 Jun 2026 14:11:18 +0000

How I Reverse-Engineered ETS2's Cargo System (And Built a Better Route Planner)

So here's something weird I discovered while building my ETS2 companion tool — the in-game cargo market isn't actually random. It pretends to be, but there's a predictable weight-distance-value triangle that SCS has been tweaking since 2012.

After pulling data from about 200 hours of gameplay and cross-referencing it against the game's economy_data.sii file, I built a route profitability calculator. The project started as a messy Python script and eventually turned into something worth sharing.

What I learned about ETS2's cargo logic:

High-value cargo (medical equipment, electronics) spawns more frequently near industrial zones with 3+ companies clustered together
The game biases urgent deliveries toward cities you've visited less — it's literally nudging you to explore the map
Scandinavia DLC cargo pays roughly 18-22% more per km than base game routes, even for identical job types

The tool basically scrapes the telemetry SDK output, matches it against a pre-mapped city database, and highlights routes that maximize per-minute earnings rather than just per-km. Nothing groundbreaking for experienced modders, but it made my long hauls way more efficient.

Actually ended up documenting the whole process with screenshots and the data structure — the economy file parsing alone is a rabbit hole I didn't expect to fall into: [insert URL]

Anyone else dug into the game files and found mechanics that aren't explained anywhere in the tutorials? Curious what else is hiding in plain sight.

Complete Marvel Rivals Strategy Guide — Tips, Mechanics & Hidden Features

dayu2333-jinyul — Tue, 09 Jun 2026 14:10:15 +0000

Building a Lethal Hero Guide Site for Marvel Rivals (Without Going Crazy on Data)

I've been maining Psylocke in Marvel Rivals for a couple weeks now and honestly, half my deaths come from not knowing which walls are about to collapse under Hela's ult. The destructible environments in this game are wild — and keeping track of breakpoints for every map is a nightmare.

So I built a small static guide site to solve my own problem, and figured I'd share the stack since some of you might be doing similar projects.

The core challenge: Rivals has 33 heroes with team-up synergies, 8 maps with dynamic sightlines, and seasonal balance patches that flip the meta overnight. That's a lot of interconnected data points.

What I landed on:

• Next.js + MDX for content — write hero guides in markdown, embed interactive matchup tables as React components
• Airtable as a CMS — non-technical friends on the team can update ability cooldowns and damage numbers without touching code. Each hero is a record, each ability is a linked table
• Static regeneration every 4 hours during patch weeks, weekly otherwise. Netlify builds are free and fast enough for this

The tricky part was modeling team-up abilities cleanly. Some heroes grant passive buffs to specific partners (Rocket + Groot is a whole different character basically), and showing those conditional synergies without cluttering the UI took a few iterations.

If you're curious about the data structure or want to see how I handled the matchup matrix, the Marvel Rivals tier list and hero guides page has the live version. Still rough around the edges but the core functionality is there.

Anyone else building tools or sites around Rivals? Curious how you're handling the destructible terrain data — I haven't found a clean way to map breakable walls per objective point yet.