microsoft/autogen · error · ArgumentException

All agents must have a unique name.

Error message

All agents must have a unique name.

What it means

GroupChat.Validation() requires all member agents to have distinct names. It collects agents.Select(x => x.Name) and, if names.Distinct().Count() != names.Count, throws ArgumentException('All agents must have a unique name.'). Names are the identity used for speaker selection and message attribution, so duplicates would make routing ambiguous.

Source

Thrown at dotnet/src/AutoGen.Core/GroupChat/GroupChat.cs:86

        this.initializeMessages = initializeMessages ?? new List<IMessage>();
        this.orchestrator = orchestrator;

        this.Validation();
    }

    private void Validation()
    {
        // check if all agents has a name
        if (this.agents.Any(x => string.IsNullOrEmpty(x.Name)))
        {
            throw new ArgumentException("All agents must have a name.");
        }

        // check if any agents has the same name
        var names = this.agents.Select(x => x.Name).ToList();
        if (names.Distinct().Count() != names.Count)
        {
            throw new ArgumentException("All agents must have a unique name.");
        }

        // if there's a workflow
        // check if the agents in that workflow are in the group chat
        if (this.workflow != null)
        {
            var agentNamesInWorkflow = this.workflow.Transitions.Select(x => x.From.Name!).Concat(this.workflow.Transitions.Select(x => x.To.Name!)).Distinct();
            if (agentNamesInWorkflow.Any(x => !this.agents.Select(a => a.Name).Contains(x)))
            {
                throw new ArgumentException("All agents in the workflow must be in the group chat.");
            }
        }
    }

    /// <summary>
    /// Select the next speaker based on the conversation history.
    /// The next speaker will be decided by a combination effort of the admin and the workflow.
    /// Firstly, a group of candidates will be selected by the workflow. If there's only one candidate, then that candidate will be the next speaker.

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Assign a distinct Name to each member, e.g. suffix loop indices ("worker-0", "worker-1").
2. Pre-validate with GroupBy before construction and fail with a clear message showing the duplicates.
3. If two agents intentionally play the same role, either rename them ("summarizer-a"/"summarizer-b") or use a single agent.
4. Note the comparison is case-sensitive: "Critic" and "critic" both pass validation, but downstream matching lowercases names, so avoid case variants too.

Example fix

// before
var members = Enumerable.Range(0, 3).Select(_ => new GPTAgent("worker", ...));
var chat = new GroupChat(admin, members);

// after
var members = Enumerable.Range(0, 3).Select(i => new GPTAgent($"worker-{i}", ...));
var chat = new GroupChat(admin, members);

var names = members.Select(m => m.Name).ToList();
var duplicates = names.GroupBy(n => n).Where(g => g.Count() > 1).Select(g => g.Key).ToList();
if (duplicates.Count > 0)
    throw new ConfigurationException($"Duplicate agent names: {string.Join(", ", duplicates)}");

try { var chat = new GroupChat(admin, members); }
catch (ArgumentException ex) when (ex.Message.Contains("unique name"))
{
    // rename the duplicate members (e.g. suffix an index) and retry
}

When it happens

Trigger: Passing two agents constructed with the same name string (e.g. two GPTAgent("assistant", ...)); generating members in a loop with a constant name; case-sensitive duplicates like "Agent" vs "Agent" (the check is ordinal, so exact matches only).

Common situations: Copy-pasted agent setup code where the name wasn't changed; factory loops creating N agents with the same label; merging agents from different modules that happen to share a default name.

Related errors

• All agents must have a name.
• All agents in the workflow must be in the group chat.
• GroupChatManager does not have a name
• No next available agents found in the current workflow
• No admin is provided.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/64e93b3c97c7a8bd. Report an issue: GitHub.