github/copilot-sdk · error · IllegalArgumentException

Expected digit in number

Error message

Expected digit in number <part> at position <pos>

What it means

The JSON number parser in CopilotToolProcessor calls requireDigit(part) after seeing '.' or 'e'/'E' to demand at least one digit in the fraction or exponent part. If the input ends or a non-digit follows, it throws this IllegalArgumentException naming which part ('fraction' or 'exponent') was missing a digit. JSON forbids literals like 1. or 1e.

Solutions

1. Complete the number: change 1. to 1.0 and 1e to 1e0 (or drop the marker).
2. Ensure the JSON source is complete before parsing (check stream/string termination).
3. Catch IllegalArgumentException and use the pos/part detail to report precisely where the number is truncated.

Example fix

// before
{"threshold": 0.}
// after
{"threshold": 0.0}

static boolean hasCompleteNumbers(String json) {
    return json.matches(".*\\d+(\\.\\d+)?([eE][+-]?\\d+)?.*")
        && !java.util.regex.Pattern.compile("\\d\\.([^\\d]|$)|\\d[eE]([^\\d]|$)").matcher(json).find();
}

static boolean completeNumberAt(String s, int i) {
    // after '.' or 'e'/'E' there must be at least one digit
    return i + 1 < s.length() && Character.isDigit(s.charAt(i + 1));
}

try {
    processor.parse(args);
} catch (IllegalArgumentException e) {
    if (e.getMessage().contains("Expected digit in number")) {
        // input likely truncated — request the remainder before retrying
    }
    throw e;
}

When it happens

Trigger: Arguments containing number literals with a dangling decimal point ("1.") or dangling exponent marker ("1e", "1e-") — the character after the marker is missing or not a digit.

Common situations: Truncated LLM output (stream ended mid-number), copy-paste of numbers formatted for humans (e.g. "5." at end of a sentence), template generation bugs.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

Related errors

• Number cannot be represented at position
• Unexpected end of JSON
• Unexpected trailing content at position
• Unescaped control character at position <pos-1>
• Unterminated string escape at position

AI-assisted analysis of github/copilot-sdk@cd8cf15dc3 (2026-09-09). Data as JSON: /api/errors/93e715f40aa88919. Report an issue: GitHub.

Appendix: source

Thrown at java/sdk/src/main/java/com/github/copilot/tool/CopilotToolProcessor.java:1140

                if (pos < input.length() && (input.charAt(pos) == '+' || input.charAt(pos) == '-')) {
                    pos++;
                }
                requireDigit("exponent");
                consumeDigits();
            }
            String number = input.substring(start, pos);
            try {
                new java.math.BigDecimal(number);
            } catch (NumberFormatException e) {
                throw new IllegalArgumentException("Number cannot be represented at position " + start + ": " + number,
                        e);
            }
            return "new java.math.BigDecimal(\"" + number + "\")";
        }

        private void requireDigit(String part) {
            if (pos >= input.length() || !isAsciiDigit(input.charAt(pos))) {
                throw new IllegalArgumentException("Expected digit in number " + part + " at position " + pos);
            }
        }

        private void consumeDigits() {
            while (pos < input.length() && isAsciiDigit(input.charAt(pos))) {
                pos++;
            }
        }

        private boolean isAsciiDigit(char c) {
            return c >= '0' && c <= '9';
        }

        private boolean isDigitOneToNine(char c) {
            return c >= '1' && c <= '9';
        }

        private void skipWhitespace() {

View on GitHub (pinned to cd8cf15dc3)