Real interviews don't come with a script. So I built an AI interviewer with a hidden personality you have to read in real-time.
I posted UnderFireAI on IH a while back and landed around #40. The product's been live at underfireai.com for a while now, but looking back, I think the actual insight got buried under the feature list. So I'm taking another swing at the pitch.
The insight
Every interview prep tool on the market gives you questions to rehearse. Real interviews aren't like that. The hardest part isn't the question — it's the human across the table. They have a mood. They have pet peeves. They have a hidden agenda. You have to read all of that on the fly, while answering.
So I built it the other way around.
What it actually does
UnderFireAI gives you an AI interviewer with a hidden personality drawn from one of 8 archetypes — the Skeptic, the Griller, the Friendly, the Silent Judge, the Rapid Fire, the Culture Fit, the Technical Expert, the Executive.
You don't see which one you're getting. You have to figure it out from how they ask questions, what they push back on, when they go quiet.
Each archetype runs on six independent personality traits — directness, depth preference, warmth, patience, technical focus, skepticism, all 0–100 — plus a live mood engine that swings between −100 and +100 based on your answers. Drop a buzzword in front of the Skeptic? Mood plummets. Give a vague answer to the Griller? They go five levels deeper. Ramble at the Rapid Fire? They cut you off.
After the session, the personality is revealed alongside the scorecard, and you can replay every message to see exactly when their mood shifted on you.
What's in the box
6 interview types — behavioral, technical, case study, HR screen, panel (multiple AI interviewers at once, each with their own archetype), phone screen
6 company styles — FAANG, startup, consulting, finance, enterprise, government — each with style modifiers (FAANG = +20 technical depth, startup = −20 formality, etc.)
Voice mode — Cartesia Sonic 3, ~40ms time-to-first-audio, 6 voices matched to interviewer personality. Voice is a different skill than typing answers, and that's the whole point.
Live coding — Judge0 sandbox, 7 languages, visible + hidden test cases, scored on correctness, efficiency, code quality, and approach
Salary negotiation simulator — separate module, AI recruiter pushes back hard, generates a "Simulated Final Offer" as a real dollar figure showing what your technique closed and what you left on the table
Resume vulnerability scanner — flags vague metrics, buzzword stacking, scope overstatement, employment gaps, then generates the exact probing questions an interviewer would ask. Resume context auto-injects into every session so the AI targets your real weak spots.
JD gap analyzer — paste a job description, get skill-gap breakdown, generate practice questions specific to the role
Custom interviewer builder — blend two archetypes, override the six trait sliders, add constraints (heavy follow-ups, time pressure, compensation pushback)
Full replay — playback controls, mood evolution chart, per-message scoring, code submission replay
3D HUD (React Three Fiber) — feature-flagged, falls back gracefully to 2D when WebGL isn't available
Outbound webhooks — HMAC-SHA256 signed
session.completedevents you can pipe into Notion, Slack, or your own dashboard
Tech stack (the honest version)
Next.js 15 + React 19 + TypeScript strict, Supabase (17 tables, RLS on everything), Stripe v17.
For the AI side: OpenRouter as the gateway, DeepSeek V3 for the live interview conversation (cheap, fast, surprisingly good at sustained personality work), Mistral Small 3.1 for analysis — deliberately a different provider so analysis calls don't collide with interview-session rate limits on DeepSeek. The Anthropic SDK isn't in the runtime at all; OpenRouter end-to-end.
Voice is Cartesia Sonic 3. Code execution is Judge0 via RapidAPI. 3D is Three.js r169 via R3F.
Pricing — the part nobody else does
Credit packs, one-time, no subscriptions, every feature unlocked with every purchase:
Starter — $25 / 6 interviews
Pro — $35 / 11 interviews
Refill — $10 / 5 interviews
This was a deliberate call. Nobody needs interview prep every month. You need it hard for a few weeks before a job hunt, then you don't think about it again for a year or two. Charging $29/mo recurring for a tool people actively want for three weeks felt wrong, and the churn would be brutal anyway. One-time packs respect the actual use case. Credits don't expire. Refill whenever.
Why I'm posting this again
The first time around I led with the feature list. That was the mistake. The product isn't the features — it's the philosophy: train under fire so the real thing feels easy. Hidden personalities. Mood that responds to every word. Voice mode where the latency makes you sweat. Resume scanner that tells you the exact questions you're going to get hammered on. Negotiation sim that produces a real dollar number at the end so you can feel what you left on the table.
If you've ever walked out of an interview thinking "I knew that — why couldn't I deliver under pressure?" — this is the tool I wish I'd had.
Two things I'd love your take on
Selling credit-pack pricing into a market trained on subscriptions — what messaging actually worked for you?
The hidden-personality mechanic is the strongest differentiator I've ever shipped, but it's the hardest to communicate cold. How would you pitch it in one sentence?
Happy to dig into the architecture, the prompt design for the personality and mood engine, or the pricing model in the comments.
— Chris underfireai.com
