TechnitiumSoftware/DnsServer · error · FormatException

Invalid AdGuard Upstreams config file format: missing ']' br

Error message

Invalid AdGuard Upstreams config file format: missing ']' bracket.

What it means

Thrown while parsing an AdGuard Upstreams config file (a separate upstream-format file, not the app JSON config) imported by the AdvancedForwardingApp. A line starting with '[' must contain a matching ']' that delimits the domain list from the upstream server(s). If no ']' is found (LastIndexOf returns -1), the file is rejected with FormatException.

Source

Thrown at Apps/AdvancedForwardingApp/App.cs:647

                        while (true)
                        {
                            line = sR.ReadLine();
                            if (line is null)
                                break; //eof

                            line = line.TrimStart();

                            if (line.Length == 0)
                                continue; //skip empty line

                            if (line.StartsWith('#'))
                                continue; //skip comment line

                            if (line.StartsWith('['))
                            {
                                int i = line.LastIndexOf(']');
                                if (i < 0)
                                    throw new FormatException("Invalid AdGuard Upstreams config file format: missing ']' bracket.");

                                string[] domains = line.Substring(1, i - 1).Split('/', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
                                string forwarder = line.Substring(i + 1);

                                if (forwarder == "#")
                                {
                                    if (defaultForwarderRecords.Count == 0)
                                        throw new FormatException("Invalid AdGuard Upstreams config file format: missing default upstream servers.");

                                    forwardings.Add(new Forwarding(defaultForwarderRecords, domains));
                                }
                                else
                                {
                                    List<DnsForwarderRecordData> forwarderRecords = new List<DnsForwarderRecordData>();
                                    string word = PopWord(ref forwarder);

                                    while (word.Length > 0)
                                    {

View on GitHub (pinned to d0484b6c1e)

Solutions

1. Open the referenced AdGuard upstreams file and add the missing ']' bracket on the indicated line, using the syntax [/domain1/domain2/] upstream1 upstream2.
2. Re-download or re-export the upstreams file from a known-good AdGuard source to restore correct formatting.
3. Validate every '['-prefixed line ends its domain section with ']' before the upstream servers.

Example fix

// before (upstreams file)
[/example.com/ 1.1.1.1
// after
[/example.com/] 1.1.1.1

// Validate each '['-prefixed line of an AdGuard upstreams file has a matching ']'.
foreach (string line in File.ReadAllLines(upstreamsPath))
{
    string t = line.TrimStart();
    if (t.StartsWith('[') && t.LastIndexOf(']') < 0)
        throw new FormatException($"AdGuard upstreams line missing ']': {line}");
}

When it happens

Trigger: An AdGuard upstreams line beginning with '[' but missing the closing ']', e.g. '[/example.com/ 1.1.1.1' or '[]example.com 8.8.8.8' written incorrectly. Any '['-prefixed line without a ']' triggers it.

Common situations: Hand-editing an AdGuard-style upstreams file and dropping the ']' bracket; truncated line from a copy-paste; wrong file format chosen for the upstream source.

Related errors

• Invalid AdGuard Upstreams config file format: missing defaul
• Invalid AdGuard Upstreams config file format: missing upstre
• Network group map contains an invalid network address: {netw
• Groups array was not defined.
• Forwarder was not defined: {forwarderName}

AI-assisted analysis of TechnitiumSoftware/DnsServer@d0484b6c1e (2026-08-13). Data as JSON: /api/errors/840ff973bacaea66. Report an issue: GitHub.