Pokémon Team Builder
A browser tool that picks the best team of six from a box of hundreds of Pokémon during a long playthrough, while respecting rules I set for my own runs: a level cap, how many fully evolved Pokémon a team may field, and which ones should still be pushed to evolve.
Open the live demo · runs in the browser, nothing to install
Why I built it
In a randomized run of Pokémon SoulGold my box held close to 300 Pokémon, each with its own level, typing, abilities and evolution state. Picking six by hand meant juggling type coverage, stat balance and progress goals at the same time, and I kept second-guessing the result. I wanted a tool that would make the trade-offs explicit, score every candidate team the same way, and show me why the winner won.
What it does
- Reads your save file. Import a
.sav and the box fills itself: species, level, nature, ability and shiny status, decoded from the game's binary format.
- Scores whole teams. Each team gets a breakdown across base stats, stat balance, typing quality, typing balance, type coverage and the run's rules, with an adjustable weight on each.
- Searches the space. A box of 300 gives billions of possible teams. The search combines seeded sampling, hill climbing and a tournament between drafts, and switches to an exact branch-and-bound search when the pool is small enough to guarantee the optimum. It runs on background threads so the page stays responsive.
- Tracks evolution goals. The tool knows which Pokémon still need to evolve to complete a line, accounting for split evolutions, regional forms, Megas and shiny lines, and nudges the team toward them.
- Models abilities and weather. Drought, Intimidate, Levitate and dozens more change how a Pokémon is valued, including weather that only applies when its setter is on the same team.
How I built it
I am a manager, not a software engineer. I acted as product owner and tester, and the code was written by an AI coding agent (Claude Code) working from my specifications.
My part of the work:
- Defining the rules. Most of the effort went into turning intuitions into precise rules. One example: a shiny Pokémon should keep evolving unless another shiny already covers its evolution line, while a shiny evolution does count for a plain pre-evolution. Rules like that only become clear once you see the tool get them wrong.
- Testing against real play. I used the tool through a full playthrough and reported every result that looked off. The commit history records 105 versions over two months, each one a specific correction.
- Insisting on regression checks. Every bug fix comes with a check in
dev-checks.js so it cannot quietly return. The suite currently runs 119 checks.
The whole app lives in one HTML file on purpose: it opens with a double-click, works offline and needs no build step, which suited a personal tool used mid-game. The trade-off is a large file (about 5,000 lines of code plus the embedded Pokédex), and a team project would split it into modules.
Run it locally
Download pokemon-team-builder.html and open it in any modern browser. Your box is saved in the browser's local storage.
To run the regression checks (requires Node.js):
node dev-checks.js
Data sources
Disclaimer
A personal fan project with no commercial use. Pokémon and all related names are trademarks of Nintendo, Game Freak and The Pokémon Company. No game files are included or distributed.
