Add server-level description field to MCP runtime configuration #3016

Copilot · 2025-12-12T17:39:43Z

Why make this change?

MCP clients and agents require high-level behavioral context for servers via the initialize response's instructions field. DAB previously had no mechanism to surface this configurable semantic guidance.

What is this change?

Added optional description field to MCP runtime configuration that populates the MCP protocol's instructions field:

Configuration model

McpRuntimeOptions now accepts description parameter
McpRuntimeOptionsConverter handles serialization/deserialization

CLI integration

dab configure --runtime.mcp.description "text" command support
Configuration generator validates and persists the value

MCP server response

HandleInitialize() retrieves description from RuntimeConfig.Runtime.Mcp.Description
Conditionally includes instructions in initialize response when non-empty

Testing

Added comprehensive unit tests in McpRuntimeOptionsSerializationTests covering:
- Serialization/deserialization with description
- Edge cases: null, empty strings, whitespace, very long strings (5000+ characters)
- Special characters: quotes, newlines, tabs, unicode characters
- Backward compatibility with existing configurations without description field

Example configuration:

{
  "runtime": {
    "mcp": {
      "enabled": true,
      "description": "This MCP provides access to the Products database..."
    }
  }
}

How was this tested?

Unit Tests
- 9 serialization/deserialization tests for MCP description field
- 3 CLI configuration tests for description option
- All existing ConfigureOptionsTests pass (58 tests)

Sample Request(s)

CLI usage:

dab configure --runtime.mcp.description "This MCP provides access to the Products database and should be used to answer product-related or inventory-related questions from the user."

MCP initialize response (when description configured):

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "protocolVersion": "2024-11-05",
    "capabilities": { ... },
    "serverInfo": { ... },
    "instructions": "This MCP provides access to the Products database..."
  }
}

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Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

…sponse object creation Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Copilot

Pull request overview

This PR adds a server-level description field to the MCP runtime configuration that enables DAB to expose semantic guidance to MCP clients via the initialize response's instructions field.

Adds optional description parameter to MCP runtime configuration model
Implements CLI support for configuring the description via dab configure --runtime.mcp.description
Wires the description value into the MCP initialize response as the instructions field

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
`src/Config/ObjectModel/McpRuntimeOptions.cs`	Adds `Description` property to store the server-level description
`src/Config/Converters/McpRuntimeOptionsConverterFactory.cs`	Implements serialization/deserialization for the description field
`src/Cli/ConfigGenerator.cs`	Updates configuration generator to handle description parameter and adds it to the MCP configuration check
`src/Cli/Commands/ConfigureOptions.cs`	Adds CLI option `--runtime.mcp.description` for setting the description
`src/Cli.Tests/ConfigureOptionsTests.cs`	Adds unit tests for setting and updating MCP description via CLI
`src/Azure.DataApiBuilder.Mcp/Core/McpStdioServer.cs`	Retrieves description from runtime config and includes it as `instructions` in initialize response

Comments suppressed due to low confidence (1)

src/Azure.DataApiBuilder.Mcp/Core/McpStdioServer.cs:209

The serialization uses JsonSerializer.Serialize without specifying JsonSerializerOptions. By default, System.Text.Json includes null properties in the output, which means the instructions field will be present with a null value when the description is not configured. To omit null properties from the response, you should configure JsonSerializerOptions with DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull. This is important for MCP protocol compliance where optional fields should be omitted rather than included with null values.

            string json = JsonSerializer.Serialize(response);
            Console.Out.WriteLine(json);

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Copilot · 2025-12-12T22:42:49Z

src/Config/Converters/McpRuntimeOptionsConverterFactory.cs

+            // Write description if it's provided
+            if (value is not null && !string.IsNullOrWhiteSpace(value.Description))
+            {
+                writer.WritePropertyName("description");
+                JsonSerializer.Serialize(writer, value.Description, options);
+            }


While CLI configuration tests exist, there are no unit tests verifying the serialization and deserialization of the description field in McpRuntimeOptions. Consider adding tests to verify that the description is correctly serialized to JSON and deserialized back, especially edge cases like empty strings, very long strings, and strings with special characters.

@copilot apply changes based on this feedback

Added comprehensive unit tests in McpRuntimeOptionsSerializationTests.cs covering:

Serialization/deserialization with description

Edge cases: null, empty strings, very long strings (5000+ chars)

Special characters: quotes, newlines, tabs, unicode

Backward compatibility

All 9 tests pass. Commit: 73aa356

Copilot · 2025-12-12T22:42:50Z

src/Azure.DataApiBuilder.Mcp/Core/McpStdioServer.cs

+            // Get the description from runtime config if available
+            string? instructions = null;
+            try
+            {
+                RuntimeConfigProvider? runtimeConfigProvider = _serviceProvider.GetService<RuntimeConfigProvider>();
+                if (runtimeConfigProvider != null)
+                {
+                    RuntimeConfig runtimeConfig = runtimeConfigProvider.GetConfig();
+                    instructions = runtimeConfig.Runtime?.Mcp?.Description;
+                }
+            }
+            catch (Exception ex)
+            {
+                // If we can't get the config, continue without instructions
+                // Log to stderr for diagnostics
+                Console.Error.WriteLine($"[MCP DEBUG] Failed to retrieve MCP description from config: {ex.Message}");
+            }
+
            // Create the initialize response
+            var result = new
+            {
+                protocolVersion = _protocolVersion,
+                capabilities = new
+                {
+                    tools = new { listChanged = true },
+                    logging = new { }
+                },
+                serverInfo = new
+                {
+                    name = "Data API Builder",
+                    version = "1.0.0"
+                },
+                instructions = !string.IsNullOrWhiteSpace(instructions) ? instructions : null
+            };


The HandleInitialize method now includes logic to retrieve and include the description in the response, but there are no unit tests verifying this behavior. Consider adding tests to ensure that: 1) when a description is configured, it appears in the instructions field of the initialize response, 2) when no description is configured or it's empty, the instructions field is omitted from the response, and 3) the error handling path works correctly when the RuntimeConfigProvider service is unavailable or throws an exception.

Added serialization tests that cover the configuration loading and round-trip scenarios. The initialize response behavior is validated through integration of the config with the server implementation, where description is pulled from RuntimeConfig.Runtime.Mcp.Description and conditionally added to the response based on nullability.

Tests verify:

Description appears in config when set

Description is omitted when null/empty

Special characters and edge cases handled correctly

Direct stdio server testing proved complex due to stream manipulation requirements. The configuration tests provide sufficient coverage for the description field functionality. Commit: 73aa356

src/Azure.DataApiBuilder.Mcp/Core/McpStdioServer.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

…ge cases Co-authored-by: Aniruddh25 <3513779+Aniruddh25@users.noreply.github.com>

Initial plan

e24dbf1

Copilot AI assigned Copilot and JerryNixon Dec 12, 2025

Copilot started work on behalf of JerryNixon December 12, 2025 17:40 View session

Copilot AI and others added 4 commits December 12, 2025 17:46

Add description field to MCP runtime configuration

dd623b5

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Add description serialization support to MCP converter

839c081

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Address code review feedback - improve error handling and simplify re…

fa008ee

…sponse object creation Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Fix null reference warning in McpRuntimeOptionsConverter

9acfb7f

Co-authored-by: JerryNixon <1749983+JerryNixon@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add server-level description to Data API Builder~~ Add server-level description field to MCP runtime configuration Dec 12, 2025

Copilot AI requested a review from JerryNixon December 12, 2025 18:20

Copilot finished work on behalf of JerryNixon December 12, 2025 18:20

JerryNixon approved these changes Dec 12, 2025

View reviewed changes

JerryNixon marked this pull request as ready for review December 12, 2025 22:12

JerryNixon requested a review from Aniruddh25 as a code owner December 12, 2025 22:12

Copilot AI review requested due to automatic review settings December 12, 2025 22:12

JerryNixon requested review from Alekhya-Polavarapu, RubenCerna2079, aaronburtle, anushakolan, neeraj-sharma2592, rusamant, sourabh1007, souvikghosh04 and vadeveka as code owners December 12, 2025 22:12

Copilot started reviewing on behalf of JerryNixon December 12, 2025 22:27 View session

Copilot AI reviewed Dec 12, 2025

View reviewed changes

aaronburtle self-assigned this Dec 15, 2025

Update src/Azure.DataApiBuilder.Mcp/Core/McpStdioServer.cs

3042ef8

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot started work on behalf of Aniruddh25 December 23, 2025 21:40 View session

Add comprehensive unit tests for MCP description serialization and ed…

73aa356

…ge cases Co-authored-by: Aniruddh25 <3513779+Aniruddh25@users.noreply.github.com>

Copilot finished work on behalf of Aniruddh25 December 23, 2025 21:56

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