Blizzard v0.7

On a par with the strongest limited Stockfish. Against Stockfish 19 at its highest limited setting (3190)
Blizzard 0.7 scored +10 =20 −10 (50%, 0 Elo) in 40 games at 0.2 s per move. Against 0.6 it is +64 Elo:
+155 =174 −80 (59.2%) in 409 games, 95% interval +39 to +90.

What's new

The evaluation corrects itself by piece placement. Since 0.4 the search has remembered how far the static
evaluation was off in positions with the same pawn structure, and nudged later evaluations by that much. Now it
also remembers this for the placement of each side's pieces (knights, bishops, rooks and queens of one color),
and corrects the evaluation by both. This one change was worth +64 Elo.

Fast testing and tuning. Two copies of the engine can now play inside one process, about 3,600 short games an
hour on two cores, with an early stop as soon as the result is clear (tools/selfplay.js). Search parameters can
be changed without rebuilding the core, and tools/spsa.js tunes them automatically.

Tested and left out (600 games each): ProbCut (−16 Elo), double and negative singular extensions (−7),
pruning quiet moves with a bad history (+3), 16 automatically tuned search parameters (−8), and twice the weight
for the new correction (+4).

Strength

Match	Games	Score	Elo difference (95% interval)
0.7 vs 0.6	409	59.2%	+64 (+39 to +90)
0.7 vs Stockfish 2800	40	81% (0.6 scored 74%)	+255 (+151 to +425)
0.7 vs Stockfish 3000	40	59% (0.6 scored 71%)	+61 (−15 to +144)
0.7 vs Stockfish 3190	40	50% (0.6 scored 45%)	0 (−77 to +77)

Stockfish 19 here is the single-threaded browser build, limited with UCI_Elo, at 0.2 s per move. Full-strength
Stockfish, without a limit, is still far stronger. These are not FIDE or CCRL ratings; they compare Blizzard
versions under the same conditions.

Downloads

File	For	SHA-256
blizzard-0.7-windows.zip	Windows 10/11, 64-bit, nothing to install	fd6379aab75fc78279d9d2b0d592512e3619de753cd674717d65c8df23316b55
blizzard-0.7-universal.zip	macOS, Linux and others, needs Node.js 18+	fa3def7de0ed1baf708a83f621538db936244a79067bac22ab929ad1ad90a77d

Unpack, then add blizzard.exe (or node blizzard-uci.js) to Arena, Cute Chess, En Croissant or any
other UCI program. Play it in the browser at sacon1s.github.io/blizzard.

Upgrading from 0.6

• Replace the old files. UCI options are unchanged.
• blizzard.exe is not code-signed: if SmartScreen warns, click More info, then Run anyway.