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FSD skill rating for AI-native full stack developers. Made for the Hacker Rank, Code Signal, CoderPad AI assisted interviews
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Anthropic
OpenAIAlways up to date with the frontier models from Anthropic and OpenAI.
Grounded in verified research
The research behind the rating
Every number below traces to a primary source — the same standard the rating holds itself to. This is what the science says about measuring developer skill, and how we built for it.
No hiring signal predicts job performance better than ~.42 — and structured, rubric-scored evaluation is what gets closest. Every diff here is graded against a hidden rubric.
Sackett, Zhang, Berry & Lievens · J. Applied Psychology (2022)
Agreement between live Elo difficulty and gold-standard IRT difficulty once 50 developers have attempted a problem — already 0.70 after just 5.
Pankiewicz · ICCE (2020)
Share of SWE-bench tasks experts threw out as flawed. Problem quality decides what a score means — every rated Develow problem passes an audit gate first.
OpenAI · SWE-bench Verified (2024)
Best AI model's solve rate on $1M of real freelance full-stack work. Cross-layer depth is what still separates engineers — so that's what we test.
Miserendino et al. · SWE-Lancer (2025)
Self-assessment is broken. We measure shipped work.
In a randomized trial — 16 experienced open-source developers, 246 real tasks — the same people who felt faster with AI were measurably slower. A rating has to come from the stopwatch and the shipped diff, not the vibes.
What developers believed — even after the study
What the stopwatch measured on the same tasks
METR randomized controlled trial (2025) · arXiv:2507.09089
Learning is the same story — unless you use AI to build understanding
Comprehension quiz scores after learning a new library. The exception: participants who used AI to ask why — conceptual questions, explanations — retained as much as hand-coders. That's the behavior the rating's AI-orchestration signal rewards.
Anthropic randomized controlled trial (2026) · arXiv:2601.20245
One number, honestly reported
Your rating climbs as your uncertainty shrinks
Every rated challenge updates your FSD Rating against the problem's learned difficulty. The shaded band is your confidence interval — it tightens the more you prove.
Illustrative trajectory. The shaded band is the ± rating deviation — it narrows as more rated challenges are completed. Ratings stay provisional until roughly 10–20 rated challenges across 3+ skill areas.
Problems get rated too
We learn how hard a problem is — fast
Every attempt rates the problem back. After five developers try a newly published challenge, its live difficulty already agrees with gold-standard psychometrics at r ≈ 0.70 — by fifty it's 0.905. Until then, the difficulty label says provisional.
Median correlation between online Elo difficulty and an IRT graded-response reference, by number of learners sampled per task — Pankiewicz, ICCE 2020 (RunCode: 50,055 attempts). Baseline shows the two published endpoints of naive solve-rate ranking.
Built for the AI era
Four dimensions the rating actually measures
AI changed software development. The engineers who thrive aren't the ones typing the most code — they're the ones who can direct AI and ship with confidence. The rating measures exactly that.
Understand systems
Read the problem and the codebase first — know the fundamentals well enough to navigate.
Direct AI effectively
Let AI do the heavy lifting while you point it at what actually matters.
Verify solutions
Run the tests and confirm the fix holds — because you know what correct looks like.
Ship with confidence
Submit production-ready work — and be able to explain exactly why it's right.
Not one skill
A full-stack fingerprint, not a single score
One scalar can't say "great at React, shaky on auth." The rating is multidimensional, so a weak layer shows — and the public number is penalized for being lopsided.
Sample profile
FSD 1760 ± 95
Where you stand
See exactly where you rank
Sample rating 1760 → Product Engineer
Under the hood
How a submission becomes a rating
Grading is server-side against a hidden reference solution — you can't self-grade, and brute-forcing submissions decays their value.
Graded 0–100
Your diff is judged against a hidden reference + rubric by the server-side grader.
Continuous Elo
That score updates your rating against the problem's learned difficulty — one attempt at a time, and every rated attempt counts.
± Uncertainty
A Glicko-style confidence interval tightens as you complete rated challenges — and can't be farmed by tanking.
Skill vector
Only the skills a problem exercises move — weighted by its rubric.
ML calibration
Offline models recalibrate difficulty and recommend your next challenge.
Try the update rule
You vs. the problem — feel the math
Your rating and the problem's learned difficulty set an expected grade; beating expectation moves you up. Drag the sliders — this is the live update rule, not a mock.
New accounts start wide (±350) — bigger swings until you're calibrated.
Hundreds of attempts have pinned this problem's difficulty — beating it means something.
E = 1 / (1 + 10^((Rₚ − Rᵤ) / 400)) — a 1500-rated dev solves a 1500-rated problem about half the time, the same difficulty semantics Codeforces uses. Your step size scales with your own uncertainty and shrinks against uncalibrated problems.
Learn freely, prove deliberately
Practice mode and Rated mode
Practice mode
Learn freely. Build the reps.
Rated mode
Prove it. This is what counts.
Speed is key
A rating that proves you can crack the AI interview
Using the exact interview IDE and AI tools used at software companies, we compiled real-world problems asked by big tech — and turned your performance into a credible, shareable rating.
HackerRank
CoderPad
CodeSignalLogos shown to reference the coding-interview formats we grew up on. Not affiliated with or endorsed by HackerRank, CoderPad, or CodeSignal.
Where speed meets maintainability
Download the free Develow IDE
Learn test-driven development with DVL AI — the methodology engineers use to ship 10x faster. Never get stuck again.
Real work, not exercises
Every rated challenge moves your number
Each mission is a real engineering job, scoped to a focused rep — across React, Node, Python, FastAPI, Go, Postgres and more.
Add search to an online store
Start mission →Fix a checkout failure
Start mission →Launch multi-language support
Start mission →Improve accessibility
Start mission →Scale for Black Friday traffic
Start mission →Ship a real-time notifications feed
Start mission →Get a free Amazon question (2026)
A real Amazon full-stack debugging OA — MovieDB I. Drop your email and we'll send it over, free.
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A clear path to product engineering
No tutorial hell. Just momentum.
- 1Month 1Day 1
Build Products
Learn how modern applications are structured and shipped. Get hands-on with frontend, backend, databases, and Docker through real, runnable projects.
- 2Month 2Day 30
Ship Features
Move beyond tutorials. Add functionality, fix bugs, and navigate real codebases — watching your FSD Rating climb with every rated challenge.
- 3Month 3Day 60
Think Like An Engineer
Work through realistic product challenges and AI-assisted workflows. Walk into any interview with a rating that proves you've already done the work.
- 1Month 1Day 1
Build Products
Learn how modern applications are structured and shipped. Get hands-on with frontend, backend, databases, and Docker through real, runnable projects.
- 2Month 2Day 30
Ship Features
Move beyond tutorials. Add functionality, fix bugs, and navigate real codebases — watching your FSD Rating climb with every rated challenge.
- 3Month 3Day 60
Think Like An Engineer
Work through realistic product challenges and AI-assisted workflows. Walk into any interview with a rating that proves you've already done the work.
Pricing
Upgrade for the full 90-day roadmap
Free
- ✓Download the Develow IDE
- ✓Run sample problems
- ✓Provisional FSD Rating
- ×Full problem library
- ×Full rated-mode scoring
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Built for every background
Frequently asked questions
Whether you come from software, design, business, or product — Develow is built to accelerate your learning rate. Speed is the whole point.
It's a single, honestly-reported number (with a ± confidence interval) that reflects how well you ship correct, verified changes in real codebases across the full stack. It starts provisional and sharpens as you complete rated challenges.
Yes. Missions start small and DVL Agent works right beside you — it can investigate the codebase, explain the architecture, and teach you how a fix works. You learn by shipping real software from day one instead of grinding abstract puzzles.
Absolutely. Designers already think in systems and user outcomes. Develow turns that instinct into shipped features — you'll learn just enough of the stack to build, with AI handling the boilerplate so you move fast.
Perfect fit. Product and business people who can direct AI to ship working software are the new force multipliers. Missions teach you to scope problems, build features, and verify they work — the core of Product Engineering.
Start building your rating today
Work through real-world problems with DVL Agent, earn your FSD Rating, and build the skills companies actually pay for.