microsoft/aspire · error · DistributedApplicationException

The ResolveWebAssemblyProjectReferences MSBuild target…

Error message

The ResolveWebAssemblyProjectReferences MSBuild target returned no output for '{serverProjectPath}'.

What it means

After ResolveWebAssemblyProjectReferences exits successfully, the method parses the target's stdout as JSON containing the client project path. When the target exits 0 but emits no output, the library throws a DistributedApplicationException because there is nothing to parse.

Solutions

Reference a Blazor WebAssembly client project from the server project so the MSBuild target emits a result.
Verify manually: run `dotnet msbuild <server.csproj> -t:ResolveWebAssemblyProjectReferences` and inspect output.
Explicitly configure the client project path in code rather than relying on MSBuild auto-discovery.
Check for custom Directory.Build.props/targets suppressing the target and remove ProjectReference ambiguity.

Example fix

<!-- before: server has no WASM client reference -->
<!-- after -->
<ItemGroup>
  <ProjectReference Include="..\Client\Client.csproj" />
</ItemGroup>

Defensive patterns

Strategy: validation

Validate before calling

var output = Process.Run("dotnet", $"msbuild {serverProjectPath} -t:ResolveWebAssemblyProjectReferences").StandardOutput;
if (string.IsNullOrWhiteSpace(output)) throw new InvalidOperationException("No WASM client project resolved; server likely lacks a Blazor WebAssembly client reference.");

Try / catch

try { await ResolveBlazorWasmClientProjectPathAsync(...); } catch (DistributedApplicationException ex) when (ex.Message.Contains("returned no output")) { logger.LogError(ex, "Server project did not resolve any WASM client"); throw; }

Prevention

Reference a Blazor WebAssembly client project from the server project.
Verify the MSBuild target emits JSON output before relying on auto-discovery.
Provide the client path explicitly when project layout is non-standard.

When it happens

Trigger: Running the MSBuild ResolveWebAssemblyProjectReferences target on a Blazor server project whose client references were not resolved (no WASM client project referenced, or the target matched nothing) so stdout is empty/whitespace.

Common situations: Blazor server project without a referenced WebAssembly client; project layout where discovery returns nothing; MSBuild target silently no-op due to wrong properties or custom SDK setup.

Understand the failure class

Background: EmptyResultError / "no results found": when an API or scraper succeeds but returns zero rows — this error's family across 9 libraries.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/21eb6218541c1610. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.Blazor/BlazorHostedExtensions.cs:245

                ? new DistributedApplicationException(message, result.StartException)
                : new DistributedApplicationException(message);
        }

        if (result.ExitCode != 0)
        {
            BlazorGatewayLog.WasmClientDiscoveryFailed(
                logger,
                serverProjectPath,
                result.StandardOutput,
                result.StandardError);
            throw new DistributedApplicationException(
                $"Failed to discover the Blazor WebAssembly client project for '{serverProjectPath}'. " +
                $"The ResolveWebAssemblyProjectReferences MSBuild target exited with code {result.ExitCode}.");
        }

        if (string.IsNullOrWhiteSpace(result.StandardOutput))
        {
            throw new DistributedApplicationException(
                $"The ResolveWebAssemblyProjectReferences MSBuild target returned no output for '{serverProjectPath}'.");
        }

        try
        {
            using var output = JsonDocument.Parse(result.StandardOutput);

            // MSBuild emits:
            // { "Items": { "WebAssemblyProjectReference": [{ "Identity": "/path/Client.csproj" }] } }
            if (output.RootElement.TryGetProperty("Items", out var items)
                && items.TryGetProperty("WebAssemblyProjectReference", out var projectReferences))
            {
                foreach (var projectReference in projectReferences.EnumerateArray())
                {
                    if (projectReference.TryGetProperty("Identity", out var identity)
                        && identity.GetString() is { Length: > 0 } projectPath)
                    {
                        return Path.GetFullPath(projectPath, serverDirectory);

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