Syntax Highlighting

The plugin provides comprehensive syntax highlighting for Circom 2.x, making your code easier to read and understand at a glance.

Highlighting Categories

Keywords

Standard Circom keywords are highlighted with the default keyword color:

pragma circom 2.0.0;

template Multiplier() {
    signal input a;
    signal output out;
    var temp;
    component sub = SubComponent();
}

function square(x) {
    return x * x;
}

Keywords include: pragma, circom, include, template, function, component, var, signal, if, else, for, while, do, return, assert, log, main, public

Signal Types

The input and output keywords receive special highlighting in blue-violet (#879DE0) to make signal direction immediately visible:

template SignalDemo() {
    signal input publicValue;
    signal input secretKey;
    signal output commitment;
    signal output nullifier;
}

Note

In Circom, input signals are values provided by the prover, while output signals are computed results that can be verified.

Constraint Operators

Circom’s constraint operators are highlighted in teal (#4EC9B0) to distinguish them from regular operators:

template ConstraintDemo() {
    signal input a;
    signal input b;
    signal output c;
    signal witness;

    // Constraint assignment (signal flow)
    c <== a * b;

    // Reverse constraint
    a * b ==> c;

    // Equality constraint
    a * b === c;

    // Non-constraint assignment
    witness <-- a + b;
    a + b --> witness;
}

Tip

Understanding constraint operators:

• <== and ==> create constraints AND assign values (signal flow)
• === creates only a constraint (equality check)
• <-- and --> assign values WITHOUT creating constraints (witness computation)

Template Modifiers

Template modifiers are highlighted in yellow (#BBB529):

pragma circom 2.0.0;
pragma custom_templates;

template parallel ParallelAdder(n) {
    signal input in[n];
    signal output out;
}

template custom CustomGate() {
    signal input a;
    signal output c;
}

bus DataBus(width) {
    signal data[width];
}

Modifiers include: parallel, custom, bus

Additional Highlighting

The plugin also highlights:

• Comments: Both line (//) and block (/* */) comments
• Strings: String literals in quotes
• Numbers: Decimal and hexadecimal numbers (123, 0x1A2B)
• Brackets: Parentheses, square brackets, and curly braces

Customizing Colors

You can customize all syntax colors through your IDE settings:

1. Go to Settings → Editor → Color Scheme → Circom
2. Adjust colors for each highlighting category
3. Changes apply immediately to all open Circom files

See Color Settings for more details.