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Measured on six things

A browser-based Sans Fight Simulator recreating Undertale...

Security

HTTPS enforced with SPF, but only 3/12 security checklist points: no HSTS, CSP, frame protection, or DMARC. No privacy policy depth or security page found. Typical for a fan project, weak for anything handling data.

Screenshots

1 / 1

Bad Time Simulator

About this app

Bad Time Simulator is a fan-made, browser-based recreation of the iconic Sans boss fight from Undertale. Developed by jcw87, it lets you practice the entire battle or individual attack patterns without replaying the main game. The simulator includes multiple modes: Normal (full fight with menus), Practice (learn patterns with health resets), Single Attack (focus on specific attacks), and Endless (continuous phase practice). It accurately mimics Sans's attacks, including Gaster Blasters, blue-soul gravity shifts, and platforming sections. While not a perfect replica—noted differences include hitbox variations and platform speed—it serves as an excellent training tool for fans looking to master the fight. The game runs directly in your browser and supports keyboard controls, with touch controls available on some devices. Whether you're a seasoned player aiming for a no-hit run or a newcomer struggling with Sans, this simulator offers a convenient way to improve your skills.

Key features

1Four practice modes: Normal (full fight with menus), Practice (per-pattern health resets), Single Attack, and Endless
2Accurate recreation of Sans's attacks including Gaster Blasters, blue-soul gravity shifts, and platforming sections
3Runs directly in the browser with keyboard controls (arrows/WASD, Z/Enter, X/Shift) and version-dependent touch support

Target customer profile

Drawn from the product itself, not from a survey.

Demographic

Undertale fans aged 13-30

Pain points

Struggling to beat Sans in the original game, limited time to replay the entire story

Primary needs

A focused practice environment to learn Sans's attack patterns

Demographic

Speedrunners and completionists

Pain points

Need to optimize dodging strategies and memorize attack sequences

Primary needs

Quick access to specific attacks for repeated practice

Demographic

Casual gamers with limited gaming time

Pain points

Difficulty finding time to reach Sans in a full playthrough

Primary needs

Instant access to the boss fight without story progression

Scout Review

Written by AI from measured evidence, scored out of 100.

Bad Time Simulator does one thing and does it well: it lets you fight Sans without replaying Undertale to get there. The four modes are genuinely useful, the Practice mode's per-pattern health reset is the feature that makes it a training tool rather than a novelty, and the controls documentation is better than it needs to be. The design is faithful to Undertale's palette but the homepage drowns the actual product in a grid of 40+ related fan fights, and the YouTube overlay on the hero sprite is a rough edge. Speed is excellent on desktop and merely okay on mobile. Security headers are thin, though the site collects nothing worth protecting. Accessibility is a genuine strength. This is a well-executed fan project with a clear purpose and an honest scope — not a product trying to be more than it is.

Measure by measure

Usability

Four clear modes (Normal/Practice/Single Attack/Endless), a documented controls table, and a genuine how-to-play guide. Practice mode's per-pattern health reset is the standout usability win.

Design

Dark Undertale-consistent palette and clear hero hierarchy, but a 30+ card related-games grid creates visual noise and the YouTube overlay on the Sans sprite feels bolted on.

Speed

Lighthouse desktop 99/100 and mobile 85/100 with CLS 0. Mobile LCP of 3.9s is the weak spot, likely from the dense thumbnail grid, but the game itself loads snappily.

Security

Accessibility

Lighthouse accessibility 100/100 and full keyboard control with documented bindings. No WCAG statement or multi-language support, and touch controls are version-dependent, but the core experience is keyboard-first by design.

Growth

A real, specific problem (can't beat Sans, no time to replay 20 hours) with a clear wedge: four practice modes and per-attack repetition. Niche is small but loyal, and the hub positioning adds reach.

Improvement areas

Homepage buries the simulator under a 30+ card related-games grid; collapse it behind a toggle to restore focus
Security headers are minimal (3/12): add HSTS, CSP, X-Content-Type-Options, and DMARC for basic hardening
Mobile LCP of 3.9s drags the mobile Lighthouse score to 85; lazy-load and compress the thumbnail grid

Design & Usability

Bad Time Simulator nails the aesthetic brief: near-black background, lime accents, pixel-art Sans front and center, exactly what an Undertale fan expects. The hero gets you into the fight fast. Where it stumbles is the surrounding page — a related-games grid so dense with 30+ near-identical thumbnails that finding the actual simulator again requires squinting. The YouTube play button stamped on Sans's chest is the kind of overlay that says 'we added this in five minutes.' Usability is the stronger half: four modes (Normal, Practice, Single Attack, Endless) cover every way you'd want to train, Practice resets health per pattern so you can actually learn, and the controls table plus how-to-play guide are more thorough than most commercial games bother with. The FAQ hiding answers behind tiny red icons is a small own-goal. For a fan project, the onboarding is genuinely thoughtful.

Speed & Security

Speed is a tale of two devices. Desktop Lighthouse hits 99/100 — the game boots fast and CLS 0 means nothing jumps around while you're dodging. Mobile drops to 85/100 with an LCP of 3.9s, and the culprit is almost certainly the wall of thumbnail images on the homepage rather than the game itself. On a phone, four seconds before first paint is long enough to reconsider your life choices. Security is where this fan project shows its seams: HTTPS is enforced and SPF is set, but that's 3 of 12 checklist points. No HSTS, no CSP, no frame protection, no DMARC, no privacy policy depth, no security page. For a browser game that stores nothing and asks for no login, the practical risk is low — there's no account to steal. But if the site ever adds leaderboards, accounts, or payments, this header posture is a starting point, not a foundation.

Accessibility & Growth

Accessibility is quietly excellent: Lighthouse scores 100/100, and the game is keyboard-first by design with arrow keys, WASD, Z/Enter, and X/Shift all documented in a clean table. Touch controls exist but are version-dependent, which is an honest caveat rather than a promise. There's no WCAG statement or multi-language support, so it's not a compliance story — it's just a game that happens to be playable by keyboard, which for this genre is most of the battle. Growth is a narrower question. The problem is real and specific: Undertale's Sans fight is famously brutal, and replaying 20 hours of story to practice it is a genuine pain. The wedge is the four practice modes, especially per-attack repetition, which the original game simply cannot offer. The ceiling is the niche — this serves Undertale fans who are stuck, and that audience is finite and aging. The hub positioning (40+ related fan fights) extends reach beyond a single game, which is the smartest growth move on the site. It won't become a business, but as a fan resource it has a clear reason to exist.

Conclusion

If you're stuck on Sans and you've already watched the same YouTube tutorial four times, this is the tool you actually want: load it, pick Practice, and grind the pattern that's killing you. The site's own notes are refreshingly honest about what it doesn't replicate — the heart hitbox, the missing dialogue, the platform speed in sans_platforms4. That transparency is worth more than a polished marketing page. The related-games hub is a nice bonus if you want more fan fights after you've beaten this one. It won't replace the original fight, and it isn't trying to. For what it is — a browser-based practice room for one very specific, very hard boss — it works, and it works without asking anything of you.

Suggestions for improvement

Collapse the 40+ related-games grid behind a 'More fan fights' toggle so the actual simulator stays the focus of the homepage
Replace the YouTube play-button overlay on the hero sprite with an integrated play affordance that matches the pixel-art style
Add HSTS, CSP, and X-Content-Type-Options headers — cheap wins that take minutes and lift the security posture from 3/12
Lazy-load the thumbnail grid and serve WebP/AVIF to pull mobile LCP down from 3.9s toward the desktop number

How we score

Alternatives comparison

Named competitors, point by point. Nobody paid to appear here or to be left out.

	Bad Time Simulator	Undertale	Deltarune	Sans Simulator (Various)
Time to reach the Sans fight	Instant — load the page and pick a mode	Hours of story and gameplay before Sans appears	N/A — Sans is not a boss in Deltarune	Varies by simulator; typically instant
Practice individual attack patterns	Yes — Practice and Single Attack modes with health resets	No — must replay the full fight from the start	No — different combat system, no Sans fight	Some offer practice modes; accuracy and features vary
Cost	Free, browser-based	Paid — full game purchase required	Free (chapters released free)	Mostly free fan projects
Full story and context	No — isolated boss fight only, no dialogue or story	Yes — complete RPG with branching narrative	Yes — full story, but no Sans boss encounter	No — fan simulators isolate the fight
Platform	Browser (keyboard; touch on some versions)	PC, consoles, Switch	PC, consoles, Switch	Mostly browser-based