github/copilot-sdk · error · ArgumentException

Invalid entry '*': there is no bare wildcard. Use `new…

Error message

Invalid {field} entry '*': there is no bare wildcard. Use `new ToolSet().AddBuiltIn("*")`, `.AddMcp("*")`, or `.AddCustom("*")` to target a specific source.

What it means

The CopilotClient constructor throws this ArgumentException when a tool filter list (AvailableTools/ExcludedTools) contains the bare wildcard entry '*'. There is no bare-wildcard semantics; you must target a specific tool source (built-in, MCP, or custom) using the ToolSet builder methods.

Solutions

Replace "*" with new ToolSet().AddBuiltIn("*"), .AddMcp("*"), or .AddCustom("*") depending on which source you want.
Omit AvailableTools entirely if you want the default tool selection.
Enumerate the specific tools you need instead of using a wildcard.

Example fix

// before
var config = new SessionConfig { AvailableTools = new List<string> { "*" } };
// after
var config = new SessionConfig { AvailableTools = new ToolSet().AddBuiltIn("*").AddMcp("*").AddCustom("*") };

Defensive patterns

Strategy: validation

Validate before calling

if (availableTools?.Contains("*") == true || excludedTools?.Contains("*") == true)
    throw new ArgumentException("Use AddBuiltIn/AddMcp/AddCustom instead of a bare '*' entry.");

Type guard

static bool HasBareWildcard(IEnumerable<string>? list) => list?.Any(e => e == "*") == true;

Try / catch

try { client = new CopilotClient(options, connection); }
catch (ArgumentException ex) when (ex.Message.Contains("bare wildcard")) { /* fix the tool list in config before retrying */ }

Prevention

Never hand-write "*" into tool lists; always use the ToolSet builder
Validate tool config files at load time
Share a single ToolSet factory to avoid divergent list construction

When it happens

Trigger: Passing a session config whose AvailableTools or ExcludedTools list (e.g. a List<string> or ToolSet string entries) contains the literal "*"; ValidateToolFilterList iterates every entry and throws on the first bare "*".

Common situations: Assuming '*' means 'all tools' as it does in some other SDKs; hand-writing config files with "tools": ["*"]; migrating from an API where a bare wildcard was allowed.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of github/copilot-sdk@cd8cf15dc3 (2026-09-09). Data as JSON: /api/errors/605cce922196540a. Report an issue: GitHub.

Appendix: source

Thrown at dotnet/src/Client.cs:950

    }

    /// <summary>
    /// Catches misuse of <see cref="SessionConfigBase.AvailableTools"/> /
    /// <see cref="SessionConfigBase.ExcludedTools"/> at the SDK boundary so
    /// callers get an actionable error rather than a silently-empty filter.
    /// The runtime treats a bare <c>"*"</c> as a literal name match for a tool
    /// whose name is the single character <c>*</c>, which the runtime's
    /// charset guard would reject at registration — so the filter effectively
    /// matches nothing.
    /// </summary>
    private static void ValidateToolFilterList(string field, IList<string>? list)
    {
        if (list is null) return;
        foreach (var entry in list)
        {
            if (entry == "*")
            {
                throw new ArgumentException(
                    $"Invalid {field} entry '*': there is no bare wildcard. " +
                    "Use `new ToolSet().AddBuiltIn(\"*\")`, `.AddMcp(\"*\")`, or " +
                    "`.AddCustom(\"*\")` to target a specific source.",
                    nameof(list));
            }
        }
    }

    /// <summary>
    /// Resolves <see cref="SessionConfigBase.AvailableTools"/> /
    /// <see cref="SessionConfigBase.ExcludedTools"/> for the wire payload,
    /// validating empty-mode requirements. <c>toolFilterPrecedence</c> is
    /// always <c>excluded</c> so SDK consumers get composable allowlist /
    /// denylist semantics.
    /// </summary>
    private (IList<string>? AvailableTools, IList<string>? ExcludedTools, OptionsUpdateToolFilterPrecedence ToolFilterPrecedence) ResolveToolFilterOptions(SessionConfigBase config)
    {
        ValidateToolFilterList(nameof(SessionConfigBase.AvailableTools), config.AvailableTools);

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