Overview

The Dev Tunnels page — labelled Signal Deck in the UI — is MCP Explorer’s built-in webhook ingress control room. It wraps Microsoft’s devtunnel CLI to create a stable public HTTPS callback URL, captures every HTTP request that arrives at that URL in real time via SSE, and lets you inspect or replay those requests without leaving the app.

Dev Tunnels Signal Deck showing summary stats, overall event pulse sparkline, and a grid of tunnel cards

The Signal Deck dashboard: summary statistics (captured events, live tunnels, unseen events, notification mode), an overall event pulse sparkline, and a card for each configured tunnel.

Prerequisites: The devtunnel CLI must be installed inside the container (or on the host when running without Docker). If it is missing or misconfigured, Dev Tunnels shows a CLI unavailable banner instead of failing silently.

Typical Workflow

  1. Create a tunnel with a name and access mode.
  2. Start the tunnel — MCP Explorer launches devtunnel host and surfaces the public webhook URL.
  3. Register the webhook URL with any external service (Stripe, GitHub, your MCP tool, a scheduler, etc.).
  4. Inspect incoming requests in real time on the inspector page.
  5. Replay any stored request to a target endpoint for debugging.

Creating a Tunnel

  1. Navigate to Dev Tunnels in the sidebar.
  2. Click Create tunnel in the top-right toolbar.
  3. Fill in the Create Dev Tunnel dialog:
Create Dev Tunnel dialog with Name field, Access dropdown set to Anonymous, and Delete-on-exit checkbox
FieldRequiredDescription
Name✅A memorable label — e.g. Stripe payouts, Agent hooks, Batch callbacks
Access—Anonymous (no token required for callers) or Authenticated (callers must present a token)
Delete on exit❌When checked, the tunnel is removed from the devtunnel service when MCP Explorer stops
  1. Click Create tunnel. MCP Explorer registers the tunnel definition and navigates to its inspector page.

Tip: Use Anonymous access when you need an external service (Stripe, GitHub Webhooks, etc.) to POST without any credentials. The devtunnel CLI host still requires a one-time sign-in.

Starting a Tunnel

Click Start on any tunnel card on the Signal Deck, or click Start tunnel in the inspector header.

Tunnel card in Running state showing name, status badge, event count, mini sparkline, and action buttons

A running tunnel card shows the Running status badge, a live event count, a mini traffic sparkline, and quick-action buttons (Inspect, Copy webhook URL, Copy curl, Stop, Delete).

Clicking Copy webhook URL or the </> (Copy curl) icon copies the value to your clipboard and confirms with a brief toast:

'Webhook URL copied' success toast notification 'Sample curl copied' success toast notification

Login Required

If the devtunnel CLI has not been authenticated yet, starting a tunnel opens the Device Code Login dialog:

Device Code Login dialog streaming devtunnel login output with a browser URL and device code to enter

The dialog opens and immediately begins streaming devtunnel login output. Once the verification URL and device code appear, open the URL in your browser, enter the code, and sign in with your Microsoft account. The dialog closes automatically once authentication succeeds and resumes the pending start operation.

Tip — skip login entirely with Docker Compose: Set HOST_DEVTUNNELS_DIR in your .env file to your host machine’s DevTunnels credentials directory and the container will inherit your existing devtunnel user login session. See the Environment Variables reference for per-OS paths.

Tunnel Statuses

StatusMeaning
StoppedTunnel is defined but not running
StartingCLI is being launched
RunningPublic URL is live and accepting traffic
LoginRequiredCLI needs authentication before it can start
ErrorStart failed — hover the card for the error message

The Signal Deck Dashboard

The main Dev Tunnels page is a live control room for all your tunnels.

Summary Statistics

MetricDescription
Captured eventsTotal webhook requests stored across all tunnels
Live tunnelsNumber of tunnels currently in Running state
Unseen while awayEvents that arrived while you were on another page
Tunnel toastsWhether the global event notification stream is Live or Paused

Overall Event Pulse

A histogram sparkline aggregating traffic across all tunnels. The busiest tunnel’s name is displayed alongside the chart.

Inspecting Events

Click Inspect on any tunnel card (or click the tunnel’s name) to open the Tunnel Inspector.

Tunnel inspector Traffic tab with EventTimeline histogram scrubber on the left and EventTape live feed on the right

The Traffic tab: a histogram scrubber (left) for timeline navigation with play/pause, and an event tape (right) showing each captured request animating in real time.

Inspector Header

The inspector header shows the Webhook URL and Tunnel URL as read-only fields — click the copy icon to put either on the clipboard, or click the </> icon to copy a ready-to-paste curl command.

Four metric cards show:

  • Captured — total events stored for this tunnel
  • SSE status — Online / Syncing / Offline
  • Latest frame — timestamp of the most recent event
  • Notifications — Live or Paused

Traffic Tab

The Traffic tab is split into two panels:

PanelDescription
EventTimelineHistogram of events over time. Click any bar to jump to that window. Use ▶/⏸ to play back events automatically.
EventTapeLive animated feed of incoming requests. Click any row to select it for detail inspection.

Archive Tab

The Archive tab provides full per-event detail.

Tunnel inspector Archive tab showing selected event with HTTP method, path, headers table, and raw JSON body in the viewer

The Archive tab: method, path, query string, headers (with sensitive values masked), content type, body size, and the full request body rendered in the JSON viewer. Sensitive headers (Authorization, cookies, API-key-style values) are automatically redacted.

Each event shows:

  • HTTP method and path
  • Query string parameters
  • Request headers (sensitive headers automatically masked)
  • Content type and body size
  • Full request body — rendered as pretty-printed JSON when the content type is application/json, otherwise as plain text

Note: Very large request bodies are stored in truncated form. When a body has been truncated the event is flagged — you will see the actual body size alongside an indicator that the displayed content is partial.

Replaying a Webhook

Any captured event can be replayed to any HTTP/HTTPS target URL for downstream testing.

  1. Select an event in the Archive tab.
  2. Click Replay.
  3. Fill in the Replay dialog:
Replay dialog with target URL field, method override dropdown, headers override section, and response showing 200 OK
FieldDescription
Target URLWhere to send the replayed request. Must be a public HTTP/HTTPS address — loopback and private IP ranges are blocked.
Method overrideOverride the original HTTP method (optional)
Headers overrideReplace or add specific headers (optional)
Body overrideReplace the body content (optional)
  1. Click Replay. The dialog shows the downstream response status code, headers, body, and round-trip duration inline.

Security: Replay requests are blocked to loopback addresses (localhost, 127.x.x.x), unspecified addresses (0.x.x.x), link-local ranges (169.254.x.x), private IP ranges (10.x, 172.16–31.x, 192.168.x), IPv6 link-local (fe80::/10), and IPv6 ULA (fc00::/7) to prevent SSRF.

CLI Unavailable State

If the devtunnel CLI is not found or is misconfigured, the Signal Deck shows a warning banner instead of failing with a generic error:

CLI unavailable warning banner explaining that the devtunnel CLI is not installed or not configured

The banner shows the specific problem (e.g. CLI not found, not authenticated). Install the devtunnel CLI and restart the container to resolve it.

Installing the devtunnel CLI

Follow the official install guide. On a first run the CLI requires a one-time sign-in; MCP Explorer’s Device Code Login dialog handles this for you.

Webhook URL Smart-fill (Tool Integration)

When a tool parameter is named webhookUrl, callbackUrl, webhook, or callback, MCP Explorer can auto-populate it from an active tunnel’s webhook URL directly in the Tools view — saving a round-trip to copy-and-paste. Only tunnels that are Running or Starting (and already have a webhook URL assigned) appear in the picker.

Tool parameter form showing a webhookUrl field pre-filled from an active Dev Tunnel via a chip picker

The chip next to a webhookUrl parameter lets you pick from any running tunnel. Selecting one fills the field instantly.

Clicking the chip opens a compact popover listing every eligible tunnel and its webhook URL:

Webhook URL chip popover listing active tunnel names and their webhook URLs for selection

Stopping and Deleting Tunnels

  • Stop — halts the devtunnel host process. The tunnel definition and all captured events are preserved. You can restart it later.
  • Delete — removes the tunnel definition from MCP Explorer (with a confirmation dialog). If Delete on exit was checked at creation time, the tunnel is also removed from the devtunnel service.

Note: Stopping a tunnel does not delete captured events. All history is retained until you delete the tunnel.

Next Steps