♠ Zolver — a free, open-source GTO poker solver

A heads-up post-flop Texas Hold'em solver written in Zig. Computes approximate Nash-equilibrium strategies on your own laptop — no subscription, no cloud, no bloat. A config file and a terminal are all you need.

$ zolver solve spot.toml --summary

Strategy summary — flop As Kd 7h

OOP to act:
  hand class    combos      check      bet 5     all-in
  two pair         2      94.6%       4.7%       0.7%
  pair             6      97.5%       1.8%       0.7%

IP vs check:
  hand class    combos      check      bet 5     all-in
  pair             6       9.3%      73.2%      17.5%
  high card        4       5.8%      48.9%      45.3%

---

What is this?

Zolver is a CFR (Counterfactual Regret Minimization) solver for heads-up Texas Hold'em. Give it two players' ranges, a flop, stack sizes, and a betting structure, and it finds the game-theoretically optimal way to play the rest of the hand — then tells you, per hand, exactly how often to check, bet, call, or fold.

It's a serious study tool for players who want to understand GTO (game theory optimal) strategy. It is not a poker bot or a real-time assistant.

Why use it?

• 🆓 Free and open source. Commercial solvers cost hundreds of dollars. This costs nothing.
• 💻 Runs on consumer hardware. Designed for laptops and desktops, not server racks.
• 🎯 Exact, no abstraction. Solves the full game tree — no card bucketing that blurs the answer.
• ⚡ Fast. Multi-threaded and SIMD-accelerated, with complete physical runout traversal.
• 🔁 Deterministic. Byte-for-byte identical results regardless of thread count.
• 📊 Actually usable output. Human-readable terminal summaries and machine-readable JSON.

Features

• Post-flop solving from any flop, turn, or river state
• Discounted CFR (DCFR) and CFR+ algorithms
• Interactive web UI — config builder (range grid, card picker, Equilab-style paste, TOML import/export) and strategy viewer (color grid, suit-averaged cells, combo drill-down, tree navigation)
• Standard range formats — QQ+, ATs+, A5s-A2s, JTs-87s, weights, just like Equilab/Flopzilla
• Human-readable summaries (--summary) — see your strategy by hand class at a glance
• JSON output — per-street strategy grids + per-hand EVs for any runout
• Helpful error messages — spot.toml:3: expected integer for 'game.initial_pot', got 'abc'
• Exploitability measurement — know exactly how close to Nash equilibrium you are
• Convergence stopping — halts once exploitability hits your target, or automatically when it plateaus at the precision floor (no wasted iterations)
• Physical runouts — evaluates every turn/river runout with private-card-aware blocking

Quick Start

First build the binary (see Installation), then alias it for convenience:

zig build -Doptimize=ReleaseFast
alias zolver=./zig-out/bin/zolver

The fast path — no text editor needed:

# 1. Build your spot in the browser (or import an existing spot.toml)
zolver config                       # range grid, card picker, paste ranges, TOML import/export
#    → download spot.toml when done

# 2. Solve it, then explore the result visually
zolver solve spot.toml -o results.json --summary
# stderr ends with: next: zolver view results.json
zolver view results.json            # interactive strategy viewer in the browser

Prefer the terminal? Start from a documented example and edit it by hand:

zolver example --output spot.toml   # writes a fully-commented config
$EDITOR spot.toml
zolver solve spot.toml --summary

Running zolver with no arguments opens the config builder automatically.

Screenshots

Config Builder	Strategy Viewer

Installation

Build from source

Requires Zig 0.16.0 on Linux (see Limitations — the thread pool uses a Linux futex, so macOS/Windows are not supported).

git clone https://github.com/phagmaier/zolver.git
cd zolver
zig build -Doptimize=ReleaseFast
./zig-out/bin/zolver example

Prebuilt Linux binaries (zolver-linux-x86_64 and zolver-linux-aarch64) are attached to each GitHub release. Releases are published automatically when a version tag v* is pushed (see .github/workflows/release.yml).

CLI Reference

zolver solve <config.toml> [flags]

Loads a config, runs the solver until convergence or max_iterations, and reports results. Flags:

Flag	Effect
--summary	Print a human-readable flop strategy overview to the terminal.
--output <path> / -o <path>	Write the full strategy tree as JSON.
--turn <card>	Also include the turn subtree for that runout, e.g. --turn 2c.
--river <card>	Also include the river subtree (requires --turn), e.g. --river Ah.
--all-runouts	Dump every canonical turn/river runout (large; per-hand EVs omitted).

Progress is printed to stderr as it solves:

loaded 'spot.toml'
  ranges: 150/180 combos  tree: 142 actions, 198 terminals  runouts: 49 turns, 2352 rivers
  memory: 45.2 MB  threads: 4
solving...
  start  exploitability: 18.234% (18.234 chips)
  iter     64  exploitability:  1.853% (1.853 chips)  4.7s
  iter    128  exploitability:  0.487% (0.487 chips)  9.5s
solve complete: 128 iterations, 0.487% exploitability, 9.5s elapsed

A compact run summary is printed to stdout:

iterations: 128
exploitability_pct: 0.487
exploitability_chips: 0.487
avg_ev_oop: 48.32
avg_ev_ip: 51.68
initial_pot: 100
elapsed_s: 9.52
converged: true

When you pass -o / --output, stderr also prints a one-line next step:

output written to 'results.json'
next: zolver view results.json

Note on EVs: after normalization by compatible range mass, avg_ev_oop and avg_ev_ip sum to initial_pot, including when a line ends all-in before the river. Turn and river chance is conditioned on the four dealt private cards: 45 cards to a flop turn, then 44 to a river.

zolver view <results.json>

Opens an interactive strategy viewer in your browser.

How to use it:

• The 13×13 grid shows the acting player's range. Each cell is color-coded by what the strategy does with that hand — green = check, orange = bet, red = fold, purple = raise, pink = all-in. Brighter = higher probability.
• Click any cell to see the strategy breakdown and EV in the detail panel. Cells with multiple combos show a suit-averaged strategy; expand the combo list in the detail panel to drill into a specific combo.
• Click the action buttons below the grid ("bet 66", "raise 110", etc.) to navigate deeper into the game tree and see how the opponent responds.
• Use the player toggle (OOP / IP / Acting) to view the other player's perspective at the same decision point.
• If you solved with --turn or --all-runouts, use the street dropdown to switch between flop, turn, and river.
• Color legend under the meta strip maps check / call / bet / raise / all-in / fold.
• Keyboard shortcuts: Backspace goes back up the tree; Escape steps out of a concrete combo, then clears the selection; arrow keys switch streets. Terminal actions (fold / lines with no child) are disabled rather than silent no-ops.
• The viewer also works standalone — open the HTML file directly and drag-and-drop any results.json onto it.

zolver config

Opens an interactive config builder in your browser. Build a complete spot without touching a text editor.

How to build a spot, step by step:

1. Pick the flop — click three cards from the 52-card deck at the top of the right panel. The selected cards appear in the board slots. The range grid automatically grays out hands that share cards with the board.

2. Set OOP's range — in the left panel ("OOP Range" tab):

   • Paste a range string (Equilab/Flopzilla style) into the box under the grid — e.g. QQ+, AKs, A5s-A2s:0.5, T9s+ — and hit Apply (or Enter). This replaces the active tab's grid. Invalid tokens toast an error and leave the previous range alone.
   • Left-click a cell to include that hand in the range (blue highlight). Click again to remove it.
   • Right-click a cell to open a weight slider — set the hand to 75%, 50%, or 25% frequency. Partially-weighted hands show a yellow tint with the percentage in the cell. Click Apply to confirm or Cancel to discard.
   • Click and drag across multiple cells to select or deselect a region of hands at once.
   • Use the preset buttons ("All Pairs", "Suited Aces", "Broadway", etc.) to quickly populate common ranges. Presets replace the current selection. ("Top N%" buttons are coarse matrix shortcuts, not true equity percentiles.)

3. Set IP's range — switch to the "IP Range" tab and repeat. The two ranges are independent.

4. Configure the game — in the right panel:

   • Set Initial Pot, Effective Stack, and Min Bet.
   • Add or remove bet sizings per street (as percentages of the pot). Click + Add to add a sizing, the × button to remove one.
   • Set raise caps per street ("none" = unlimited raising).

5. Configure the solver — algorithm, max iterations, target exploitability, thread count, SIMD, prune options, and DCFR parameters (hidden when CFR+ is selected).

6. Export / Import — the TOML Preview panel updates live as you edit. Click Copy to Clipboard or Download spot.toml, then run:

   zolver solve spot.toml -o results.json --summary
   zolver view results.json

   Incomplete spots (missing flop or empty ranges) are blocked from export. Use Import TOML (header) or Import file… / Import preview under the preview to reload an existing spot.toml back into the builder.

zolver example [--output <path>]

Prints a fully-documented example config to stdout (or to a file).

zolver help

Prints usage.

Output formats

--summary (terminal)

A range-weighted breakdown of the strategy at the key flop decision points — OOP's opening action and IP's responses — grouped by made-hand class on the flop (set+, two pair, pair, high card). Perfect for a quick read of "what should I do with this kind of hand here?"

--output results.json (machine-readable)

The full per-hand strategy tree, ready to feed into a script, notebook, or your own viewer. The flop tree (runout-independent) is always included; turn/river subtrees are added on demand with --turn/--river, or exhaustively with --all-runouts.

{
  "meta": {
    "flop": "As Kd 7h", "initial_pot": 100, "effective_stack": 200,
    "iterations": 128, "exploitability_pct": 0.487,
    "ev_oop": 48.32, "ev_ip": 51.68, "converged": true
  },
  "streets": [
    {
      "street": "flop", "board": "As Kd 7h",
      "nodes": [
        {
          "id": 87, "player": "oop", "line": [],
          "actions": ["check", "bet 50", "all-in"],
          "hands": [
            { "combo": "AhKh", "strategy": [0.05, 0.40, 0.55], "ev": 142.3 }
          ]
        }
      ]
    }
  ]
}

strategy lines up positionally with actions; line is the action path from the root to that node. Bet/raise amounts are in chips.

Config File Reference

The config uses a TOML-like format. Sections and keys are required unless marked optional. Bad configs report the exact line and reason, e.g. spot.toml:3: expected integer for 'game.initial_pot', got 'abc'.

[game]

Key	Type	Description
flop	string	Three flop cards, space-separated. Format: rank + suit (As Kd 7h). Ranks: 2-9, T, J, Q, K, A. Suits: s, h, d, c.
initial_pot	integer	Pot size (in chips) at the start of flop betting.
effective_stack	integer	The smaller of the two remaining postflop stacks.
min_bet	integer	Minimum bet/raise increment in chips. Optional, default: 1.
max_budget_bytes	integer	Total retained solver-memory limit before a solve starts: tables, storage, and thread-dependent working arenas. Optional, default: 8 GB. Increase for large trees with many sizings/raises; lower to avoid excessive swap on low-memory machines.
compress_suits	boolean	Solve using canonical suit-isomorphic turn/river runouts while exactly remapping private-hand reaches and values. Optional, default: true. Set false only to use the full physical-runout correctness oracle.

[game.sizings]

Bet size fractions as percentages of the pot, per street. An empty list [] means only check and all-in are available. Values must be strictly increasing per street.

Key	Type	Description
flop	integer array	Bet sizes on the flop (e.g., [25, 50, 75] for 25%, 50%, 75% of pot).
turn	integer array	Bet sizes on the turn.
river	integer array	Bet sizes on the river.

[game.raise_cap]

Maximum number of raises per street. Use none or unlimited (or omit the key) for no cap. Use 0 to disallow raises (check/call/fold only).

Key	Type	Description
flop	integer or none	Max raises on the flop.
turn	integer or none	Max raises on the turn.
river	integer or none	Max raises on the river.

[ranges]

Player hand ranges with frequencies. Format: HAND[SUFFIX][:WEIGHT], comma-separated. The same notation Equilab and Flopzilla export.

Single hands:

• AK — all 16 combos (suited + offsuit)
• AKs — suited only (4 combos)
• AKo — offsuit only (12 combos)
• 88 — pocket pair (6 combos; suffix ignored for pairs)

Plus ranges:

• QQ+ → QQ, KK, AA
• ATs+ → ATs, AJs, AQs, AKs (ace fixed, kicker climbs)
• T9s+ → T9s, JTs, QJs, KQs, AKs (gap preserved, climbs to ace)

Dash ranges:

• 99-66 → 99, 88, 77, 66
• A5s-A2s → A5s, A4s, A3s, A2s
• JTs-87s → JTs, T9s, 98s, 87s

Weights: append :VALUE (0.0–1.0) to play a hand a fraction of the time. Default is 1.0. Applies to plus/dash ranges too (QQ+:0.5).

Key	Type	Description
oop	string	Out-of-position player's preflop range.
ip	string	In-position player's preflop range.

Examples:

oop = "QQ+, AKs, AQs+, AJo+, T9s+, 88:0.5"
ip  = "JJ+, AKs, KQs, A5s-A2s:0.5"

[solver]

Key	Type	Default	Description
algorithm	string	—	"dcfr" (recommended) or "cfr_plus".
max_iterations	integer	1000	Hard cap on solve iterations.
target_exploitability_pct	float	0.5	Stop when exploitability reaches this % of the initial pot.
num_threads	integer	0	Worker threads. 0 = serial. 4 = 3 workers + main thread.
prune_zero_reach	boolean	false	Skip subtrees where the opponent has zero probability mass. Safe to enable.
use_simd	boolean	true	Use SIMD vectorized kernels (8-wide f32). Recommended.
check_interval	integer	64	Exploitability re-check cadence after iterations 32, 64, 128.
stall_patience	integer	5	Stop early after this many exploitability checks with no real improvement (the solve has hit the precision floor). 0 disables.
stall_rel_improvement	float	0.01	Minimum fractional drop in exploitability that counts as progress for stall_patience.
debug_invariants	boolean	true (Debug)	Run NaN/Inf scans of regret arrays after every pass.

[solver.dcfr]

DCFR discounting parameters. Only used when algorithm = "dcfr".

Key	Type	Default	Description
alpha	float	1.5	Discount exponent for positive regrets.
beta	float	0.0	Discount exponent for negative regrets.
gamma	float	2.0	Strategy averaging weight exponent.

Complete example

[game]
flop = "As Kd 7h"
initial_pot = 100
effective_stack = 200
min_bet = 1
max_budget_bytes = 8589934592  # 8 GB — increase for large trees
compress_suits = true          # Set false only for physical-runout oracle checks

[game.sizings]
flop = [25, 50, 75]
turn = [25, 50]
river = [50, 100]

[game.raise_cap]
flop = 1
turn = none
river = 1

[ranges]
oop = "QQ+, AKs, AQs+, AJo+, T9s+, 88:0.5"
ip  = "JJ+, AKs, KQs, A5s-A2s:0.5"

[solver]
algorithm = "dcfr"
max_iterations = 1000
target_exploitability_pct = 0.5
num_threads = 4
prune_zero_reach = true
stall_patience = 5            # stop early once exploitability plateaus (0 = off)
stall_rel_improvement = 0.01

[solver.dcfr]
alpha = 1.5
beta = 0.0
gamma = 2.0

How It Works

Algorithm

Zolver uses Discounted CFR (DCFR) with parameters α=1.5, β=0, γ=2 — the configuration recommended by Brown & Sandholm (2019) for fastest convergence in large games. Each iteration, one player updates their regrets while the opponent plays their current strategy, then the roles swap. Strategies are extracted from accumulated positive regrets via regret matching.

Game tree

The tree is built from the betting structure you specify. Action nodes branch on every legal action (check, fold, call, bet, raise, all-in); chance nodes deal the turn and river; terminal nodes are folds or showdowns.

Suit isomorphism

By default (compress_suits = true) the solver collapses suit-symmetric turn/river runouts into canonical representatives, exactly remapping each player's private-hand reaches and returned values for every orbit member — so board-blocking semantics are preserved and the result matches the full physical traversal. This is where the memory savings on symmetric boards come from (monotone flops shrink the runout tables ~71%). Set compress_suits = false to evaluate the complete physical 49×48 space directly as a correctness oracle; rainbow flops have no board symmetry, so the two modes coincide there.

Exploitability

Exploitability measures how far a strategy is from Nash equilibrium, in chips per hand and as a percentage of the initial pot. Lower is stronger. The solver stops automatically once it drops below target_exploitability_pct.

Performance

The end-to-end baseline below was measured on Linux with 8 solver threads, ReleaseFast, DCFR with α=1.5, β=0, γ=2, at commit 669702c. Each result is the median of three 128-iteration runs after one warm-up. Every spot traverses all 49 turns and 2,352 ordered turn-river runouts; memory is total retained solver memory plus thread-dependent working arenas.

Kernel throughput (bench.zig micro-benchmarks)

Kernel	Scalar	SIMD	Speedup
Regret matching	1,005 Mslots/s	11,504 Mslots/s	11.5×
DCFR regret update	2,757 Mslots/s	12,939 Mslots/s	4.7×
Strategy accumulation	1,727 Mslots/s	10,570 Mslots/s	6.1×
Showdown sweep	—	—	319 Mhands/s

End-to-end physical-runout baseline (8 threads, 128 forced iterations)

Spot	Tree	Total memory	ms/iter	Exploitability @128
SRP dry (rainbow)	288A / 389T	764.6 MB	271	1.2902%
SRP two-tone	288A / 389T	764.6 MB	296	0.7528%
SRP monotone	288A / 389T	764.6 MB	295	0.9446%
3-bet dry	204A / 269T	346.9 MB	127	0.7857%
SRP, three sizings	1,108A / 1,613T	3,611.4 MB	1,267	2.3985%
SRP, raise cap 2/1/1	372A / 493T	920.1 MB	357	1.6058%

These are the physical-oracle numbers (compress_suits = false), so texture does not change runout-table size or total memory — the matched rainbow, two-tone, and monotone spots all traverse the complete physical chance space, and their small runtime difference is board-specific evaluation work. With the default compress_suits = true, symmetric boards shrink dramatically (two-tone 466.2 MB, monotone 221.9 MB) while rainbow is unchanged. Extra bet sizes remain the dominant capacity lever. Memory and exploitability match the pre spin-then-park baseline; wall ms/iter is at least as fast.

A separate thread-pool characterization (wall + CPU time per phase at 1/2/4/8 threads) lives in bench/README.md: the solve iteration still pins ~7.9 cores and scales ~6× on 8 threads, while the adaptive spin-then-park pool drops exploit/output cores_busy from ~8.0 toward ~1–2 (workers park during serial work instead of burning cores).

Limitations

• Linux only. The thread pool parks idle workers on a raw Linux futex (a deliberate trade-off to keep the pool allocation-only — see src/threading.zig), so the code does not build on macOS or Windows.
• Heads-up only. Multi-way pots are not supported.
• Post-flop only. The solver always begins at the flop; preflop solving is out of scope.
• No abstraction. It solves the full game tree with no card bucketing — exact, but the tree can grow large with many bet sizes.
• ~0.2% exploitability floor. Regret/strategy storage is f32, which keeps memory light but caps how close to Nash a solve can get (~0.2% of pot for DCFR). Convergence is fast to that floor; the solver then stops automatically rather than spinning. This is within the range commercial solvers are commonly run to. See bench/README.md.

Project Status

The solver is complete and tested (238 tests) — tree construction, threaded DCFR, best response, exploitability, SIMD kernels, suit compression, JSON export, terminal summaries, and the browser config builder / strategy viewer. Convergence is cross-validated against TexasSolver (see bench/).

Building

Requires Zig 0.16.0. The project is a single Zig package (build.zig) exposing several steps, plus a few standalone measurement binaries and helper scripts.

Build steps (zig build <step>)

Step	Command	Purpose
(default)	zig build	Debug build → zig-out/bin/zolver (assertions + debug_invariants NaN/Inf sweeps enabled).
(default, release)	zig build -Doptimize=ReleaseFast	Optimized build — use this for anything you actually run or time.
run	zig build run -- solve spot.toml --summary	Build and launch the CLI; everything after -- is forwarded to zolver.
test	zig build test	Full test suite (238 tests: unit, suit-compression parity, serial-vs-threaded determinism, spin-then-park pool). Runs in ReleaseSafe (all asserts/bounds checks kept, just optimized — the solver tests iterate real CFR, so this is ~6× faster than Debug with identical results). Add -Dtest-filter=<substr> to run a subset, or -Dtest-optimize=Debug for the fully unoptimized run (also enables the Debug-only invariant sweeps).
bench-threads	zig build bench-threads -- <spot.toml> [flags]	Thread-pool benchmark: wall and CPU time for the solve / exploitability / output passes at 1/2/4/8 threads. Always compiles ReleaseFast. Flags: --iters N --warmup N --exploit-reps N --output-reps N. Prints JSON to stdout, a table to stderr.

Standalone measurement binaries (zig run)

These time work rather than assert; they're intentionally excluded from zig build test.

Command	Purpose
zig run -OReleaseFast src/bench.zig	Kernel microbenchmarks (regret matching, DCFR update, strategy accumulation, showdown sweep) plus one full CFR iteration with a memory-bandwidth figure.
PERF_ITERS=40 PERF_THREADS=8 zig run -OReleaseFast src/perf_profile.zig	Runs only the solve hot path in a tight loop, for profiling under perf record --call-graph dwarf.

Benchmark & validation scripts (bench/)

Command	Purpose
python3 bench/run_bench.py [spot.toml ...]	End-to-end solve benchmark over bench/spots/ → bench/out/results.md + JSON. One warm-up + three median samples; asserts the full 49-turn / 2,352-runout space.
bench/run_thread_bench.sh [spot.toml ...]	Runs bench-threads across the texture spots → bench/out/threads/ (+ a combined summary.md).
TEXASSOLVER_DIR=/path/to/TexasSolver bench/run_validation.sh v1 v1b v2	Cross-validates flop strategies against TexasSolver v0.2.0.

See bench/README.md for methodology, results, and how the harness has caught real bugs.

License

MIT — see LICENSE for details.

Acknowledgments

This project draws on the academic literature on CFR and its variants:

• Zinkevich et al. (2008) — Regret minimization in games
• Brown & Sandholm (2019) — Discounted CFR
• Tammelin (2014) — CFR+
• Johanson et al. (2012) — Suit isomorphism for poker