In development Features, engine behaviour and interface details are still changing. Everything here runs locally in your browser.
Current Generation Available

THE NEW GENERATION OF THE XO5 ENGINE

XO5 FORGE V3 PRO

PVS Search • Aspiration Windows • Advanced Threat Analysis • Smarter Search • Enhanced Transposition Tables

Engineered for deeper tactical perception and search efficiency. Features Principal Variation Search, multi-generational transposition tables, history heuristics, and solver-grade VCF/VCT threat detection.

01
Principal Variation Search

Scouts non-PV candidate branches with narrow null windows, saving search effort and reserving full-width evaluations for verified improvements.

02
Aspiration Windows

Searches within tight score brackets centered around previous iteration results to prune branches earlier during iterative deepening.

03
Advanced Move Ordering

Combines PV priority, two-slot killer moves, opponent counter-move tables, and side-specific history heuristics to evaluate strong moves first.

04
Generational Transposition Tables

Employs depth-priority and generation aging replacement schemes with secondary-hash validation to maximize cache efficiency and prevent collisions.

05
Enhanced Threat Analysis

10-tier tactical pattern classification with defensive urgency scoring to evaluate four-threats, open threes, and complex double-threat combinations.

06
VCF / VCT Support

Specialized solver probes for forced victory-by-continuous-four and continuous-threat lines, capable of finding forced mates before negamax search.

07
Tactical Verification

Dual-phase pre-search tactical verification probes that instantly confirm winning lines, forced defensive blocks, and mitigate opponent forks.

08
9-Level Difficulty System

Graded AI ladder from beginner-friendly exploratory play at Level 1 up to maximum tactical depth and unbounded calculation at Level 9.

Runs in your browser. No account, no install.

Build five in a row before the engine does.

A 15×15 strategy game with nine AI levels to play against, a live read on who is winning, a separate analysis board, and solver-verified puzzles you can play or generate locally.

1–9
AI levels
225
Squares in play
1s – ∞
Search budget
Sample position Move 14 · X to play
Last move played Square the engine would pick

A still illustration, not a live game. The real board is in Play and Analysis.

ENGINE FAMILY

XO5 Forge

The tactical engine family powering XO5.

XO5 Forge V3 PRO

The current engine powering XO5. Built on the V3 architecture and upgraded with stronger search, tactical analysis, and verification.

  • Advanced PVS Search
  • Aspiration Windows
  • Improved Transposition Table
  • History & Counter-Move Heuristics
  • Advanced Threat Analysis
  • Stronger VCF/VCT & Tactical Verification
Current Generation
Available

XO5 Forge V3

Stable previous-generation engine. Reliable alpha-beta search with iterative deepening, VCF/VCT tactical solver, and full analysis support.

  • Alpha-Beta Search
  • Iterative Deepening
  • Transposition Table
  • VCF/VCT Solver
  • Threat Analysis
Previous Generation · Available

XO5 Forge V4

Next-generation Forge engine. Coming soon.

Coming Soon

XO5 Forge V4 PRO

Future flagship Forge variant. Coming soon.

Coming Soon

Start here

Choose how you want to play

Five ways into the same board. Pick one and you are playing in a second — there is nothing to set up first.

The engine

Nine AI opponents, one real engine

Choose an AI level from Beginner to Maximum when you play. Analysis is a separate board for inspecting positions after the game or exploring your own variations.

  • No level throws the game. Every level from 1 to 9 takes an immediate win when one is on the board, and blocks one when it is not.
  • Two workers, no freezing. The move search and the position analysis run on separate background threads, so the page stays responsive while the engine thinks.
  • Stop whenever you want. A search on the infinite budget runs until you end it.

AI level select

Choose your opponent before a game

Selected

Level 7

Depth reached

12

Time used

0.9s

Engine’s choice on the board

Analysis

See the position the way the engine sees it

Scores are always shown from X’s point of view: positive means X is better, negative means O is better. One convention, everywhere, so a number never means two different things.

  • Evaluation bar and graph. A bar beside the board and a line through the whole game, both updating as each search depth completes.
  • Candidates and principal variation. The shortlist the engine considered, ranked, plus the line it expects to follow.
  • Move grading. Each move is labelled Best, Good, Inaccuracy or Blunder from the swing in evaluation it caused.
  • Proven mates. Forced wins are shown as M1, M2… only once the tactical solver has verified them.

Engine panel

What sits beside the board while you play

worker
+1.4Advantage X · depth 14

Candidate moves

Evaluation over the game

Puzzles

Prove a win. Then make your own.

Play solver-verified positions in a focused Puzzle Mode, or open Puzzle Lab to generate short forced wins locally. The live mini-board follows the candidate while the forcing solver checks it.

  • Your move is verified live. The engine re-checks the position after you play, rather than comparing against a stored answer.
  • A daily pick. One puzzle from the bank is surfaced each day.
  • Generate and stop anytime. Accepted mate-in-1/mate-in-2 positions are saved immediately to your local bank and can be exported.

Puzzle Lab

Live board · mate-in-2 cap

Forced win available

Also in the box

The rest of what is here

Two players, one board

Hand the device back and forth. The engine stays out of it, but undo, history and analysis are all still there.

Search budget per move

Time controls, including none

Give the engine a second or let it run until you stop it. There is also an optional per-player game clock for display.

Progress that stays on your device

Win rate, streaks, level milestones and puzzle progress are kept in this browser’s local storage. Nothing is uploaded.

How to play

If you have played tic-tac-toe you already know most of it. The board is just bigger, and you need five.

  1. X always moves first. Players alternate, placing one mark on any empty square.
  2. Five in a row wins — horizontally, vertically or diagonally.
  3. Watch the threats. An unblocked line of three or four is usually the whole game.
  4. A full board with no five is a draw, though on 225 squares that almost never happens.

An engine project that grew a front end

This started as a search engine for five-in-a-row and turned into somewhere to play it. It is a personal project, still under active development, and the interface will keep changing. The evaluation you see is the engine’s actual output — nothing on this page is a mock-up of a feature that does not exist.

Board

15 × 15, five to win

Search

Alpha-beta, iterative deepening

Runs

Entirely client-side