BitOfTech Expenses, an MCP server in .NET

Source code for the blog series Building MCP Servers in .NET for AI Agents on bitoftech.net.

The sample is a Model Context Protocol server for expense reports and approvals. It starts as a console application with two tools and in-memory data, and ends as a secured service running in Azure that four different AI clients can call.

The series

Part	Post	Tag
1	What is the Model Context Protocol? An Introduction for .NET Developers	no code
2	Building Your First MCP Server in C#	part-02
3	MCP Tools, Resources and Prompts in .NET	part-03
4	Wiring MCP Tools to Azure SQL and External APIs	part-04
5	Hosting an MCP Server in ASP.NET Core with Streamable HTTP	part-05
6	Building an MCP Client and AI Agent in .NET	part-06
7	Securing an MCP Server with Microsoft Entra ID	part-07
8	Deploying an MCP Server to Azure Container Apps	part-08
9	Connecting an MCP Server to Microsoft Foundry Agent Service	part-09
10	Observability, Cost Control and MCP Security	part-10

main always holds the latest state. To get the code exactly as it appears in a given post, check out that post's tag:

git checkout part-02

What the server exposes

Tools:

Tool	Added in
search_expense_reports	Part 2
get_expense_report	Part 2
convert_currency	Part 4
create_expense_report	Part 4
submit_expense_report	Part 4
approve_expense_report	Part 7
notify_employee	Part 8

Resources:

Resource	Added in
expenses://policy	Part 3
expenses://reports/{reportId}	Part 3

Prompts:

Prompt	Added in
review_expense_report	Part 3

Clients

The same server, unchanged, is called by all four of these:

Client	From
VS Code Copilot	Part 2
BitOfTech.Expenses.Agent, written in the series	Part 6
Claude	Part 8
Microsoft Foundry Agent Service	Part 9

Prerequisites

1. The .NET 10 SDK.
2. VS Code with the GitHub Copilot extension. The free Copilot tier is enough.
3. An Azure subscription, from Part 4 onwards, for Azure SQL on the free offer. Parts 1 to 3 need nothing but the SDK and VS Code. A docker-compose.yml is included if you would rather run SQL Server locally.
4. A Microsoft Entra tenant where you are allowed to register applications, from Part 7 onwards.

Running it

Start at part-02 or part-03. Those two tags are self contained. Clone, build, open the folder in VS Code, and the bitoftech-expenses server appears in the MCP server list. Start it, switch Copilot Chat to Agent mode, and ask something like:

Which expense reports has Sara submitted?

git clone https://github.com/tjoudeh/building-mcp-servers-dotnet.git
cd building-mcp-servers-dotnet
git checkout part-02
dotnet build

From Part 4 onwards the code expects resources that belong to whoever is running it. main and the later tags carry my endpoints, my tenant id and my client ids in .vscode/mcp.json and in each appsettings.json. You cannot reach any of them.

So treat Part 4 and later as code to read alongside the post, and create your own resources by following the Azure CLI commands in it. Then put your own values in the configuration files.

Project layout

src/BitOfTech.Expenses.Mcp/     the MCP server
  Models/                       expense report, line and employee
  Data/                         EF Core context, queries and seed data
  Migrations/                   EF Core migrations, from Part 4
  Contracts/                    the shapes returned to the model
  Tools/                        tools the model can call
  Resources/                  

... [View full README on GitHub](https://github.com/tjoudeh/building-mcp-servers-dotnet#readme)