Getting Started

Z3’s JavaScript bindings provide both high-level (Z3Py-like) and low-level (C-like) APIs. This guide covers the high-level API, which is recommended for most use cases.

Quick Start

Create a simple Z3 program:

example.js

const { init } = require('z3-solver');

(async () => {
  // Initialize Z3
  const { Context } = await init();
  const { Solver, Int, And } = new Context('main');

  // Create variables
  const x = Int.const('x');

  // Create solver and add constraints
  const solver = new Solver();
  solver.add(And(x.ge(0), x.le(9)));

  // Check satisfiability
  const result = await solver.check();
  console.log('Result:', result); // sat

  // Get model
  if (result === 'sat') {
    const model = solver.model();
    console.log('x =', model.eval(x).toString());
  }
})();

High-Level API Overview

The high-level API provides a clean, object-oriented interface similar to Z3Py.

Initialization

Always start by initializing Z3:

const { init } = require('z3-solver');
const { Context } = await init();
const { Solver, Int, Real, Bool } = new Context('main');

The init() function is async because it loads the WebAssembly module.

Creating Variables

const x = Int.const('x');
const y = Int.const('y');
const z = Int.const('z');

Building Expressions

const { Int, And, Or, Not } = new Context('main');

const x = Int.const('x');
const y = Int.const('y');

// Arithmetic
const sum = x.add(y);
const diff = x.sub(y);
const prod = x.mul(y);

// Comparisons
const constraint1 = x.gt(0);        // x > 0
const constraint2 = y.le(10);       // y <= 10
const constraint3 = x.eq(y.add(5)); // x == y + 5

// Boolean operations
const formula = And(
  x.gt(0),
  y.le(10),
  x.add(y).eq(15)
);

Solving Constraints

const solver = new Solver();

// Add constraints
solver.add(x.add(y).eq(10));
solver.add(x.gt(y));

// Check satisfiability
const result = await solver.check();

if (result === 'sat') {
  const model = solver.model();
  console.log('x =', model.eval(x).toString());
  console.log('y =', model.eval(y).toString());
} else if (result === 'unsat') {
  console.log('No solution exists');
} else {
  console.log('Unknown');
}

Common Examples

Example 1: Solving Linear Equations

Solve the system:

x + y = 10
x - y = 2

const { init } = require('z3-solver');

(async () => {
  const { Context } = await init();
  const { Int, Solver } = new Context('main');
  
  const x = Int.const('x');
  const y = Int.const('y');
  
  const solver = new Solver();
  solver.add(x.add(y).eq(10));
  solver.add(x.sub(y).eq(2));
  
  if (await solver.check() === 'sat') {
    const model = solver.model();
    console.log('x =', model.eval(x)); // x = 6
    console.log('y =', model.eval(y)); // y = 4
  }
})();

Example 2: Boolean Logic

Solve: (p ∨ q) ∧ (¬p ∨ ¬q)

const { Context } = await init();
const { Bool, Solver, And, Or, Not } = new Context('main');

const p = Bool.const('p');
const q = Bool.const('q');

const solver = new Solver();
solver.add(And(
  Or(p, q),
  Or(Not(p), Not(q))
));

if (await solver.check() === 'sat') {
  const model = solver.model();
  console.log('p =', model.eval(p).toString()); // p = false
  console.log('q =', model.eval(q).toString()); // q = true
}

Example 3: Bit-Vector Arithmetic

const { Context } = await init();
const { BitVec, Solver } = new Context('main');

const x = BitVec.const('x', 8);
const y = BitVec.const('y', 8);

const solver = new Solver();
solver.add(x.add(y).eq(BitVec.val(255, 8)));
solver.add(x.ugt(y)); // unsigned greater than

if (await solver.check() === 'sat') {
  const model = solver.model();
  console.log('x =', model.eval(x).asSignedValue()); // as decimal
  console.log('y =', model.eval(y).asSignedValue());
}

Example 4: Using Simplifiers

From src/api/js/examples/high-level/simplifier-example.ts:

const { Context } = await init();
const { Int, Solver, Simplifier, Params } = Context('main');

// Create and configure parameters
const params = new Params();
params.set('elim_and', true);
params.set('max_steps', 1000);

// Create simplifier
const simplifier = new Simplifier('solve-eqs');

// Compose simplifiers
const s1 = new Simplifier('solve-eqs');
const s2 = new Simplifier('simplify');
const composed = s1.andThen(s2);

// Add simplifier to solver
const solver = new Solver();
solver.addSimplifier(s1);

const x = Int.const('x');
const y = Int.const('y');
solver.add(x.eq(y.add(1)));
solver.add(y.eq(5));

const result = await solver.check();
if (result === 'sat') {
  const model = solver.model();
  console.log('x =', model.eval(x).toString()); // x = 6
  console.log('y =', model.eval(y).toString()); // y = 5
}

Example 5: Parsing SMT-LIB2

const { Context, em } = await init();
const z3 = Context('main');

const x = z3.BitVec.const('x', 256);
const y = z3.BitVec.const('y', 256);
const expr = x.add(y).mul(x.add(z3.BitVec.const('z', 256)));

const solver = new z3.Solver();
solver.add(expr.eq(z3.Const('test', expr.sort)));

const result = await solver.check();
if (result === 'sat') {
  const model = solver.model();
  // Get S-expression representation
  const modelStr = model.sexpr();
  console.log('Model:', modelStr);
  
  // Parse back from SMT-LIB2 format
  const exprs = z3.ast_from_string(modelStr);
}

Context Isolation

Z3 contexts are isolated from each other. TypeScript types enforce this at compile time:

const { Int: Int1 } = new Context('context1');
const { Int: Int2 } = new Context('context2');

const x = Int1.const('x');
const y = Int2.const('y');

// This will fail to compile in TypeScript:
// x.ge(y); // Error: contexts don't match

Working with Multiple Contexts

Use templated functions to propagate types:

function add<Name extends string>(
  a: Arith<Name>, 
  b: Arith<Name>
): Arith<Name> {
  return a.add(b).add(5);
}

Asynchronous Operations

Long-running operations are async and run in separate threads. Only one can run at a time.

These operations are async:

solver.check()
solver.check(assumptions)
solver.consequences()
tactic.apply()

// Queue up operations
const result1 = await solver1.check();
const result2 = await solver2.check(); // Waits for result1

Using SMT-LIB2 Format

You can parse and work with SMT-LIB2 strings:

const { Context } = await init();
const z3 = Context('main');

// Parse SMT-LIB2 expressions
const smt = '(declare-const x Int) (assert (> x 0))';
const exprs = z3.from_string(smt);

const solver = new z3.Solver();
solver.add(...exprs);
const result = await solver.check();

TypeScript Support

The bindings include full TypeScript definitions:

import { init } from 'z3-solver';
import type { Context, Solver, Arith } from 'z3-solver';

const { Context } = await init();
const { Int, Solver } = new Context('main');

const x: Arith<'main'> = Int.const('x');
const solver: Solver<'main'> = new Solver();

Memory Management

Z3’s WebAssembly module manages memory automatically. Objects are garbage collected when no longer referenced.

For long-running applications, consider periodically creating fresh contexts to avoid memory buildup.

Error Handling

try {
  const result = await solver.check();
  // ...
} catch (error) {
  console.error('Z3 error:', error);
}

Python

C++

C

Java

.NET

JavaScript/TypeScript

Go

OCaml

Quick Start

High-Level API Overview

Initialization

Creating Variables

Building Expressions

Solving Constraints

Common Examples

Example 1: Solving Linear Equations

Example 2: Boolean Logic

Example 3: Bit-Vector Arithmetic

Example 4: Using Simplifiers

Example 5: Parsing SMT-LIB2

Context Isolation

Working with Multiple Contexts

Asynchronous Operations

Using SMT-LIB2 Format

TypeScript Support

Memory Management

Error Handling

Next Steps

API Reference

Examples

Low-Level API

Source Examples

Build docs developers (and LLMs) love

Python

C++

C

Java

.NET

JavaScript/TypeScript

Go

OCaml

​Quick Start

​High-Level API Overview

​Initialization

​Creating Variables

​Building Expressions

​Solving Constraints

​Common Examples

​Example 1: Solving Linear Equations

​Example 2: Boolean Logic

​Example 3: Bit-Vector Arithmetic

​Example 4: Using Simplifiers

​Example 5: Parsing SMT-LIB2

​Context Isolation

​Working with Multiple Contexts

​Asynchronous Operations

​Using SMT-LIB2 Format

​TypeScript Support

​Memory Management

​Error Handling

​Next Steps

API Reference

Examples

Low-Level API

Source Examples

Build docs developers (and LLMs) love

Quick Start

High-Level API Overview

Initialization

Creating Variables

Building Expressions

Solving Constraints

Common Examples

Example 1: Solving Linear Equations

Example 2: Boolean Logic

Example 3: Bit-Vector Arithmetic

Example 4: Using Simplifiers

Example 5: Parsing SMT-LIB2

Context Isolation

Working with Multiple Contexts

Asynchronous Operations

Using SMT-LIB2 Format

TypeScript Support

Memory Management

Error Handling

Next Steps