gchq/CyberChef · error · OperationError

Error: Base argument must be between 2 and 36

Error message

Error: Base argument must be between 2 and 36

What it means

Thrown by From Charcode when the Base argument is outside 2-36. The operation uses parseInt(bites[i], base), which only accepts bases in that range. The check runs before parsing any character codes, so it fires regardless of input content. This mirrors the From Base radix constraint.

Source

Thrown at src/core/operations/FromCharcode.mjs:58

            }
        ];
    }

    /**
     * @param {string} input
     * @param {Object[]} args
     * @returns {ArrayBuffer}
     *
     * @throws {OperationError} if base out of range
     */
    run(input, args) {
        const delim = Utils.charRep(args[0] || "Space"),
            base = args[1];
        let bites = input.split(delim),
            i = 0;

        if (base < 2 || base > 36) {
            throw new OperationError("Error: Base argument must be between 2 and 36");
        }

        if (input.length === 0) {
            return new ArrayBuffer;
        }

        if (base !== 16 && isWorkerEnvironment()) self.setOption("attemptHighlight", false);

        // Split into groups of 2 if the whole string is concatenated and
        // too long to be a single character
        if (bites.length === 1 && input.length > 17) {
            bites = [];
            for (i = 0; i < input.length; i += 2) {
                bites.push(input.slice(i, i+2));
            }
        }

        let latin1 = "";

View on GitHub (pinned to 4290ea7539)

Solutions

1. Set the Base arg to a supported value (commonly 16 for hex, 10 for decimal).
2. For Base64 text, use the From Base64 operation instead.
3. Validate the base in calling code before invoking.

Example fix

// before: base 64 (not supported)
fromCharcode.run(input, ['Space', 64]) // throws
// after: base 16 for hex charcodes
fromCharcode.run(input, ['Space', 16])

const base = args[1];
if (base < 2 || base > 36) {
  // clamp/fix the base; do not call fromCharcode.run()
}

function isValidCharcodeBase(b) {
  return Number.isInteger(b) && b >= 2 && b <= 36;
}

try {
  fromCharcode.run(input, args);
} catch (e) {
  if (e.type === 'OperationError' && /Base argument must be between/.test(e.message)) {
    // set Base to 16 (hex) or 10 (decimal); use From Base64 for base-64
  } else throw e;
}

When it happens

Trigger: Setting the Base arg below 2 or above 36; passing 0, 1, or 64; a recipe configured for base-64 charcodes (which is not supported here).

Common situations: Confusing charcode base with Base64 encoding; typo in the Base field; programmatic recipe with an unvalidated base value.

Related errors

• Error: Radix argument must be between 2 and 36
• Length must be greater than 0
• Bit length must be at least 2
• Error: Base argument must be between 2 and 36
• Invalid block cipher mode: ${mode}

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/fa9868eae757930d. Report an issue: GitHub.