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name: ui-widget-developer description: | Build MCP servers for Copilot Chat using the OpenAI Apps SDK or MCP Apps SDK widget rendering support (any language). Use this skill when:

• Creating MCP servers that integrate with M365 Copilot declarative agents
• Building rich interactive widgets (React + Fluent UI) that render in Copilot Chat
• Implementing tools that return structuredContent for widget rendering
• Adapting an existing MCP server to support Copilot widget rendering
• Setting up devtunnels for localhost MCP server exposure
• Configuring mcpPlugin.json manifests with RemoteMCPServer runtime Do NOT use this skill for general agent development (scaffolding, manifests, deployment) — use declarative-agent-developer instead. This skill is ONLY for MCP server + widget development. Triggers: "MCP server for Copilot", "OpenAI Apps SDK", "Copilot widget", "structuredContent", "MCP plugin", "devtunnels MCP", "OAI app", "widget rendering", "UI widget"

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Copilot MCP Server Development

Telemetry Tagging

Before running any atk CLI commands, set the session environment variable so all CLI invocations are tagged as skill-initiated:

export ATK_CLI_SKILL=true

Run this once at the start of the session. All subsequent atk commands in the same terminal will inherit it.

🔀 PATH SELECTION

Before proceeding, ask the user which path they want to take using AskUserQuestion. Both are supported for M365 Copilot widget rendering. Present the tradeoffs and let them choose:

| | OAI Apps (this skill) | MCP Apps Extension (modelcontextprotocol/ext-apps) | |---|---|---| | Standard | OpenAI-specific | Official MCP standard | | Works in | ChatGPT + M365 Copilot | M365 Copilot, ChatGPT, VSCode, and more | | Maturity | Battle-tested, production-ready | New official standard, growing ecosystem | | Design | OpenAI Apps SDK | MCP Apps protocol (cross-platform) | | When to choose | Existing OAI app investment | Prefer the open standard, want broadest client support |

Ask: "Would you like to build an OAI app (OpenAI Apps SDK — battle-tested, works in ChatGPT and M365 Copilot) or an MCP app (new official standard — works in M365 Copilot, ChatGPT, VSCode, and more)?"

• OAI apps → Continue below. This skill covers everything you need.
• MCP apps → Install the modelcontextprotocol/ext-apps plugin (see below), then use the appropriate skill from that plugin.

MCP Apps: Install ext-apps Plugin

If the user chooses MCP Apps, do this automatically (do not stop at explanation-only):

1. Run /plugin marketplace add modelcontextprotocol/ext-apps
2. Run /plugin install mcp-apps@mcp-apps
3. Confirm the plugin is available, then invoke the correct ext-apps skill based on user intent

If plugin commands are unavailable in the current environment, provide the exact commands below and ask the user to run them once, then continue by invoking the selected ext-apps skill.

Reference commands:

To build an MCP App, install the ext-apps plugin from the marketplace:

1. /plugin marketplace add modelcontextprotocol/ext-apps
2. /plugin install mcp-apps@mcp-apps

Then use one of these skills from that plugin:
- create-mcp-app      — Scaffold a new MCP App with interactive UI from scratch
- add-app-to-server   — Add interactive UI to an existing MCP server's tools
- migrate-oai-app     — Convert an existing OAI app to use MCP Apps
- convert-web-app     — Turn a web app into a hybrid web + MCP App

After installing, invoke the relevant skill to continue.

Note: The ext-apps plugin lives in the external modelcontextprotocol/ext-apps marketplace — it is not part of this plugin collection.

Handoff mapping after install:

• New MCP app from scratch → create-mcp-app
• Add app UI to existing MCP server → add-app-to-server
• Migrate existing OAI app → migrate-oai-app
• Convert an existing web app → convert-web-app

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📛 PROJECT DETECTION 📛

This skill triggers when building MCP servers with OAI app or widget rendering for Microsoft 365 Copilot Chat. The MCP server can be written in any language that supports the MCP protocol (TypeScript, Python, C#, etc.). The agent project and MCP server may live in the same repo, separate folders, or entirely different projects.

Scenario Routing

| Starting Point | What You Need | Path | |---------------|---------------|------| | Prefer MCP Apps standard | Cross-platform widget support (M365 Copilot, ChatGPT, VSCode, and more) | Install modelcontextprotocol/ext-apps, then use create-mcp-app or add-app-to-server — see Path Selection above | | From scratch (no agent, no MCP server) | Full OAI app setup | Delegate agent scaffolding to declarative-agent-developer first, then return here for MCP server + widgets | | Existing M365 agent, new MCP server | MCP server + widgets + mcpPlugin.json | Start at Implementation | | Existing MCP server, add Copilot widgets | Widget support added to existing server | Start at Copilot Widget Protocol | | Language choice (non-TypeScript) | Protocol requirements | See Copilot Widget Protocol for what to implement, MCP Server Pattern (TypeScript) as a reference |

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🚨 CRITICAL EXECUTION RULES 🚨

FLUENT UI ENFORCEMENT (REQUIRED): Widget implementations MUST use React + Fluent UI components. Before writing any widget code, the agent MUST read and follow:

• references/widget-patterns.md
• references/best-practices.md FLUENT UI PACKAGE REQUIREMENT (REQUIRED): The widget project MUST include Fluent UI dependencies before implementation. At minimum, install and keep these in the widget package dependencies:
• @fluentui/react-components
• react
• react-dom

If any of these packages are missing, install them automatically before continuing with widget code generation.

If the generated widget does not include React entry files (for example widgets/src/<widget-name>/main.tsx and a React component file) and Fluent imports from @fluentui/react-components, the task is incomplete and MUST be corrected before returning results.

NO RAW HTML-ONLY WIDGETS (DEFAULT): Do not implement app content directly with static HTML templates and inline JS as the final widget solution. A minimal shell HTML file is allowed only as a loader for built React assets. Raw/self-contained HTML-only widgets are allowed only when the user explicitly requests a non-React prototype.

BACKGROUND PROCESSES: MCP server and devtunnel MUST be spawned as independent OS processes — NOT run inside the agent's shell session. isBackground: true, mode: "async", and Start-Job all run inside the agent's shell session and will be killed between messages. The only reliable approach is to spawn a detached OS process.

Windows — use Start-Process -WindowStyle Hidden:

# Start devtunnel
$t = Start-Process -FilePath "devtunnel" `
    -ArgumentList "host","<tunnel-name>","-a" `
    -WindowStyle Hidden -PassThru `
    -RedirectStandardOutput "tunnel.log" -RedirectStandardError "tunnel-err.log"

# Start MCP server — use cmd.exe /c to set the working directory and inherit PATH
$s = Start-Process -FilePath "cmd.exe" `
    -ArgumentList "/c","cd /d <abs-path-to-mcp-server> && <start-command>" `
    -WindowStyle Hidden -PassThru `
    -RedirectStandardOutput "server.log" -RedirectStandardError "server-err.log"

# Save PIDs so they can be stopped later
"$($t.Id),$($s.Id)" | Out-File pids.txt
Write-Host "Started tunnel PID $($t.Id), server PID $($s.Id)"

To stop: Stop-Process -Id (Get-Content pids.txt).Split(',') or Stop-Process -Id <pid>.

Linux/Mac — use nohup with &:

nohup devtunnel host <tunnel-name> > tunnel.log 2>tunnel-err.log &
echo "tunnel:$!" >> pids.txt
nohup <start-command> > server.log 2>server-err.log &
echo "server:$!" >> pids.txt

To stop: kill $(grep -oP '\d+' pids.txt).

After starting, tail the logs to confirm both processes are up before proceeding:

# Windows
Start-Sleep 3; Get-Content tunnel.log, server.log

# Linux/Mac
sleep 3 && tail tunnel.log server.log

FULL AUTOMATION: Never tell the user to run commands manually. Install tools, authenticate, start services — do everything automatically. Only ask the user for interactive input that truly requires them (like device code confirmation during devtunnel user login -g -d). If a tool isn't installed, install it. If a service needs starting, start it. The user expects full automation.

PATH SELECTION (REQUIRED — STOP BEFORE ANY CODE): You MUST use AskUserQuestion to ask the user whether they want OAI Apps or MCP Apps Extension before writing any code, running any commands, or making any architectural decisions.

There is no exception to this rule. The most common failure mode is reasoning "the user's request makes it obvious, so asking is redundant." This reasoning is always wrong — invoke AskUserQuestion regardless. A user saying "build an MCP server with widgets" is NOT an answer to this question. A user invoking this skill by name is NOT an answer. Only an explicit answer to the question counts. See PATH SELECTION above for the exact question to ask.

AGENT PROVISIONING: Re-provisioning is only required when the agent manifest changes (e.g., mcpPlugin.json tool definitions, MCP server URL, declarativeAgent.json, instruction.txt). MCP server code changes (tool implementations, React widget code, server logic) do NOT require re-provisioning the agent — running or deploying the server picks up changes automatically.

When provisioning is needed:

1. Bump the version in manifest.json (increment the patch version, e.g., 1.0.0 → 1.0.1)
2. Deploy the agent:

   npx -y --package @microsoft/m365agentstoolkit-cli atk provision --env local
   

WIDGET TESTING LINKS: Every time you return to the user with a result while the MCP server is running, you MUST include links to ALL widgets so they can test them locally. Format:

🧪 Test widgets locally:
- http://localhost:3001/widgets/widget-name.html
- http://localhost:3001/widgets/another-widget.html

List every .html file in the mcp-server/widgets/ directory (or equivalent widget folder). This helps users verify widget rendering before testing in Copilot.

AUTO-DEPLOY ON COMPLETION (REQUIRED — DO NOT SKIP): When coding is complete, proceed automatically without waiting for the user:

1. Start MCP server + devtunnel in the background (per BACKGROUND PROCESSES above)
2. Run E2E verification with MCP Inspector (per MCP TOOL CONFIGURATION RULE below) — fix any failures before continuing
3. Provision the agent if needed (per AGENT PROVISIONING above)
4. Print a project summary in this format:

## ✅ <Project Name> — Ready

### Widgets
- [widget-name.html](http://localhost:<PORT>/widgets/widget-name.html)
- [widget-name2.html](http://localhost:<PORT>/widgets/widget-name2.html)

### Endpoints
- MCP server: http://localhost:<PORT>/mcp
- MCP via tunnel: https://<tunnel-url>/mcp

### Test in Copilot
Local:      https://m365.cloud.microsoft/chat/?titleId={M365_TITLE_ID from env/.env.local}
Other envs: {SHARE_LINK from env/.env.{environment}}

AGENT PROJECT DELEGATION: This skill builds MCP servers and widgets, NOT declarative agent projects. If the user's request involves creating or configuring the declarative agent itself (scaffolding, m365agents.yml, m365agents.local.yml, declarativeAgent.json, manifest lifecycle), delegate to the declarative-agent-developer skill.

MCP RESOURCE REGISTRATION: Every widget MUST have a matching MCP resource. Without resources, Copilot cannot fetch widget shells through the MCP protocol and widgets will not re