Can AI build a workout tracker app like Hevy?

Build me a personal workout tracker web app. Requirements:

- A single-page app: plain HTML, CSS, and vanilla JavaScript. No framework, no build step, no account, no server. All data stored in the browser via localStorage.
- An exercise list I build myself (name, e.g. "Bench Press"), reusable across workouts.
- Log a workout as a date plus a set of exercises, each with multiple sets (weight and reps per set).
- A "repeat last workout" action that pre-fills a new workout with the same exercises and previous weights/reps, so I only edit what changed.
- Handle these cases correctly, not just the simple "log today's workout" one:
  1. Viewing an exercise's history: show weight/reps progression over time correctly ordered by date, even if workouts weren't logged in perfect chronological order.
  2. A set logged with 0 reps or a skipped set: exclude it from personal-best/volume calculations rather than counting it as a real set.
  3. Editing a past workout's weights: recalculate that exercise's personal-best (heaviest weight, most reps at a weight) if the edited set changes it.
- A per-exercise personal-best view (heaviest weight ever, most reps at that weight).
- A one-click "export all data to JSON" button — this is the backup, since there is no account or server.
- No rest timers, no exercise video library, no social/sharing features.
- Nothing that requires publishing, an App Store, or any account of any kind. This only needs to run in my own browser.
- Include a short README explaining that data lives only in this browser and how to export/restore it.
  Keep the whole thing well under 500 lines — this is a personal tool, not a product.

What is the short answer?

Yes. Hevy’s core value is fast, frictionless logging mid-workout — you pick a routine, log sets as you go, and it auto-fills your previous weights so you always know what you did last time. None of that requires an AI feature running inside the app; it’s data entry, date-based lookups, and arithmetic (volume = weight × reps, summed across sets).

Because there’s no AI feature at runtime, there’s no ongoing API cost either. A personal build is free to run indefinitely once it exists, which makes the cost comparison against Hevy’s subscription straightforward: you pay once in build time, then nothing.

What should the first version include?

Build this for yourself only. No accounts, no social feed, no store submission.

• Create and save routines (a named list of exercises with target sets/reps)
• Log actual sets during a workout, with the previous session’s weight and reps shown as a starting point
• Automatic total volume per workout and simple PR detection (heaviest weight, most reps, or best estimated 1RM per exercise)
• A basic progress chart per exercise over time
• Local storage with export

Leave out the social feed, muscle-distribution visualizations, Apple Watch app, and Android/iOS native builds for version one. A responsive web app covers logging from your phone at the gym without any of that.

What can AI build reliably?

• The logging form and auto-fill. Pulling your last session’s numbers for a given exercise and pre-filling the input is straightforward lookup logic AI coding tools write correctly without much guidance.
• Volume and PR math. Total volume, estimated one-rep max formulas (like Epley or Brzycki), and “is this a new PR” checks are well-defined calculations with no ambiguity for AI to misjudge.
• Progress charts. Turning your logged history into a line chart per exercise is a standard charting task.
• Routine management. Creating, editing, and reordering exercises within a routine is ordinary CRUD logic AI handles reliably.

Where will AI need human help?

• Speed under real conditions. The entire point of a workout logger is that it doesn’t slow you down between sets. You’ll need to actually use it during real workouts and flag anything that adds friction — extra taps, slow loading, awkward number inputs — because that’s a usability judgment, not something AI can predict from a spec.
• Exercise list scope. Deciding which exercises to include, and how to name variations (barbell vs. dumbbell bench press, for instance) is a personal call based on what you actually train.
• 1RM formula choice, if you want it. Different estimated-1RM formulas give slightly different numbers; pick one and stay consistent rather than expecting AI to tell you which is “correct” — there isn’t a single right answer.
• Privacy. Workout data is personal but not sensitive the way medical data is. Local browser storage is a reasonable default for a single-user tool; you don’t need the account infrastructure a public fitness app would.

How long will it take and what will it cost?

Rough prototype: An evening (4–6 hours) with an AI coding tool gets you routine creation, set logging with auto-fill, and basic volume/PR tracking working.

Dependable daily-use version: A couple more evenings, mostly spent making the logging flow fast enough to actually use mid-workout — bigger touch targets, fewer taps per set, a rest timer if you want one — plus adding the progress charts.

Cost comparison: Hevy Pro runs roughly $2.99–4.99/month or $23.99–39.99/year, with a $74.99 lifetime option, depending on region and current promotion. A personal build has zero ongoing API cost since nothing calls an AI model at runtime, so the break-even point against even Hevy’s cheapest tier is essentially the time you spend building it.

Which AI tool or approach should I use?

• Lovable or a similar conversational web builder: A solid fit for getting a working logging app deployed quickly without touching code, especially for the routine and logging screens.
• Claude or ChatGPT (conversational build): Good for iterating on the exact logging flow through conversation, particularly useful when you’re testing the app mid-workout and want to describe what felt slow.
• Cursor (AI-assisted code editor): Best if you want fine control over the logging UI’s responsiveness and input handling once you’re past the initial prototype, since speed here is a UI-performance problem more than a features problem.

Like Structured, there’s no AI feature running inside the app itself — tool choice matters for how you prefer to iterate, not for any model capability gap.

What will I need to maintain?

• Hosting. A static web app with client-side storage runs free on most hosting platforms.
• Backups. Export your workout history periodically — a lost or cleared browser means lost training data if it’s only stored locally.
• No API costs. With no AI model called at runtime, there’s no usage to monitor or bill for.
• Exercise list upkeep. You’ll add new exercises or variations as your training changes; this is a quick, occasional edit, not ongoing maintenance.

Should I build it, buy it, or reduce scope?

Build it if you mainly want fast set logging, auto-filled previous weights, and basic volume/PR tracking, and you’re fine using a personal web app instead of a native app.

Buy Hevy if you want the social feed, a large pre-built exercise library with muscle-group filtering, native Apple Watch support, or you’d rather not spend a weekend building and testing a logger yourself.

Reduce scope if even routines feel like more than you need: a version that’s just a running list of “date, exercise, weight, reps” with no routines or auto-fill is an hour-long build and covers basic tracking without any of the logging-flow complexity.

What if I wanted to ship this to other people?

That’s a bigger project than the personal build above. You’d need accounts and authentication, a real backend database instead of local storage, a properly licensed exercise library if you want broad coverage, social features if you want a feed, and App Store or Play Store review for a native mobile app. Treat the personal build as a prototype for that idea, not a shortcut to it.

Starter build specification

• User: You, for your own use.
• Problem: Replacing Hevy’s paid workout logging with a personal tool.
• Core workflow: Pick a routine → log each set’s weight and reps, pre-filled from last time → see volume and PR updates automatically → check progress on a chart later.
• Required features: Routine creation, set logging with auto-fill, volume/PR tracking, progress charts, data export.
• Deliberate exclusions: No accounts, no social feed, no native watch app, no app store submission.
• Data ownership: All entries stored locally in the browser; exportable as CSV/JSON at any time.
• Definition of done: You can log a real workout start to finish without it slowing you down, and your volume/PR numbers match what you’d calculate by hand.

Sources and verification

Free-tier limits (4 routines, 7 custom exercises, 3 months of graph history) and Pro pricing of $2.99/month, $23.99/year, or $74.99 lifetime are reported in a 2026 Hevy review by Sensai, sourced from Hevy’s own Pro comparison and help documentation. A separate August 2026 check of Hevy’s U.S. App Store listing confirms the same free-tier limits and notes an additional $3.99/month SKU. A May 2026 comparison from AI Tools Bakery reports slightly higher figures ($4.99/month, $39.99/year), consistent with pricing varying by region and promotion rather than a single fixed price. This article was reviewed against current AI coding tool capabilities but the build itself was not tested end-to-end; treat build time estimates as informed projections, not measured results.

Reviewed on September 16, 2026.