mcp-resource-subscriber

CLI probe for MCP resources/subscribe — connects to any MCP Streamable HTTP server, subscribes to a resource, receives the live update notification, and re-reads the updated content.

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Install

# recommended (no install):
pnpm dlx mcp-resource-subscriber --url <mcp-server-url> --uri <resource-uri>

# fallback if pnpm is unavailable:
npx mcp-resource-subscriber --url <mcp-server-url> --uri <resource-uri>

# or install globally:
npm install -g mcp-resource-subscriber
mcp-resource-subscriber --url <mcp-server-url> --uri <resource-uri>

Note: A reference MCP test server used during compatibility verification is also included in this repository (Docker Compose). See the Lab Server section below.

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CLI Usage

Against copilot-review-mcp

mcp-resource-subscriber \
  --url http://127.0.0.1:8080/mcp/copilot-review \
  --uri copilot-review://watch/<watch_id> \
  --timeout-ms 900000

copilot-review-mcp is the @scottlz0310/copilot-review-mcp server. Replace <watch_id> with the ID returned by start_copilot_review_watch.

Against the bundled test server

# Start the test server first:
docker compose up --build
# or: npm run dev

mcp-resource-subscriber --url http://127.0.0.1:8089/mcp

Note: test://review/status is the default resource URI and is only meaningful against the bundled test server. For any other MCP server, always pass --uri explicitly.

Options

  --url <url>         MCP server Streamable HTTP endpoint (required)
                      Env: MCP_PROBE_URL
  --uri <uri>         Resource URI to subscribe to
                      Default: test://review/status (bundled test server only)
                      Env: MCP_PROBE_URI
  --auth-token <tok>  Bearer token for Authorization header
                      Prefer MCP_PROBE_AUTH_TOKEN env var (flag is visible in
                      process lists and may be stored in shell history)
                      Env: MCP_PROBE_AUTH_TOKEN (recommended)
  --skip-resource-list-check
                      Skip resources/list and assume the URI exists.
                      Use for servers with dynamic resources not in list.
                      Env: MCP_PROBE_SKIP_LIST_CHECK=true
  --timeout-ms <ms>   Notification wait timeout in ms (default: 15000)
                      Env: MCP_PROBE_TIMEOUT_MS
  --version, -v       Print version and exit
  --help, -h          Print this help and exit

Structured output

Every run emits machine-parseable lines:

capabilities {"subscribe":true,"listChanged":true}
resource-found true
resource-uri <resource-uri>
server-url <url>
initial
<initial resource text>
route subscription
subscribed true
notification-received true
unsubscribed true
recommended_next_action READ_REVIEW_THREADS
error-code null
notification <resource-uri>
final
<updated resource text>
phase-summary route=subscription url=<url> uri=<uri>

Note: recommended_next_action is only emitted when the final resource text contains it (e.g., from copilot-review-mcp). It is omitted for the bundled test server.

On failure:

error-code SERVER_URL_UNKNOWN
phase-summary route=failed url=unknown error-code=SERVER_URL_UNKNOWN

error-code RESOURCE_NOT_FOUND
phase-summary route=timeout url=<url> uri=<uri> error-code=RESOURCE_NOT_FOUND

error-code NOTIFICATION_TIMEOUT
phase-summary route=timeout url=<url> uri=<uri> error-code=NOTIFICATION_TIMEOUT

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Lab Server

Minimal MCP Streamable HTTP server for testing whether MCP clients correctly handle resources/subscribe and notifications/resources/updated.

This repository is meant to be a reproducible issue / compatibility lab for CLI AI agents such as Codex CLI, Gemini CLI, OpenCode, GitHub Copilot CLI, Claude Code, Goose, and Crush.

Purpose

The server exposes one fixed MCP resource:

test://review/status

Initial content:

status: pending
version: 1
message: Waiting for simulated review result.

After a client subscribes to the resource, the server waits for MCP_TEST_UPDATE_DELAY_SECONDS, changes the resource, and sends:

{
  "method": "notifications/resources/updated",
  "params": {
    "uri": "test://review/status"
  }
}

Updated content:

status: reviewed
version: 2
message: Simulated review result is now available.

Why Resources/Subscribe Instead Of Tools/Call

tools/call is useful for explicit actions, but many agent workflows depend on context that changes after the original request. Polling every source is noisy and client-specific. MCP resource subscriptions give clients a protocol-level way to learn that a known context object changed and should be re-read.

Examples where subscription behavior matters:

• Copilot review result
• PR review thread
• CI status
• Codecov comment
• GitHub issue discussion
• local build/test result

This test server focuses on whether the client notices a resource update, re-runs resources/read, and reflects the new content in the agent loop / model context.

Start

docker compose up --build

MCP URL:

http://127.0.0.1:8089/mcp

For local development:

npm install
npm run dev

Configuration

Environment variable	Default	Description
MCP_TEST_PORT	8089	TCP port the server listens on
MCP_TEST_PATH	/mcp	Additional MCP endpoint path. The server always registers /mcp; this adds a second path (e.g. /mcp/subscribe-probe for gateway routing). Both paths share the same MCP handler.
MCP_TEST_UPDATE_DELAY_SECONDS	5	Seconds to wait before sending the resource update notification
MCP_TEST_INITIAL_STATUS	pending	Initial value of the status field in the resource
MCP_TEST_UPDATED_STATUS	reviewed	Value of status after the simulated update
MCP_TEST_SEND_LIST_CHANGED	false	Also send notifications/resources/list_changed after the update
MCP_TEST_LOG_LEVEL	debug	Log verbosity (debug / info / warn / error / silent)

If MCP_TEST_SEND_LIST_CHANGED=true, the server also sends notifications/resources/list_changed after the simulated update.

Expected Client Behavior

An ideal MCP client should follow this flow:

initialize
  ↓
resources/list
  ↓
resources/read test://review/status
  ↓
resources/subscribe test://review/status
  ↓
receive notifications/resources/updated
  ↓
resources/read test://review/status again
  ↓
reflect updated status: reviewed in agent context

Server Capabilities

The initialize response advertises:

{
  "resources": {
    "subscribe": true,
    "listChanged": true
  }
}

Implemented MCP Messages

• initialize
• resources/list
• resources/read
• resources/subscribe
• resources/unsubscribe
• notifications/resources/updated
• notifications/resources/list_changed when MCP_TEST_SEND_LIST_CHANGED=true

No tools are implemented.

Logs

The server logs each important message so client behavior can be checked objectively:

[initialize] client connected
[resources/list] requested
[resources/read] uri=test://review/status version=1
[resources/subscribe] uri=test://review/status
[resource/update] uri=test://review/status version=2
[notification/send] notifications/resources/updated uri=test://review/status
[resources/read] uri=test://review/status version=2
[resources/unsubscribe] uri=test://review/status

The key evidence for resource subscription support is:

resources/subscribe was received
notification was sent
resources/read was received again after the notification

Tests

npm test

The test suite verifies:

• resources/list returns test://review/status
• initial resources/read returns version 1
• resources/subscribe triggers an internal update to version 2
• notifications/resources/updated is received
• updated resources/read returns version 2

Standalone Subscription Probe Client

The repository also includes a reusable MCP SDK client that exercises the full subscription flow against a running server:

npm run probe:subscribe -- --url http://127.0.0.1:8089/mcp

After npm run build, the same client can be run directly with Node:

node dist/src/client/cli.js --url http://127.0.0.1:8089/mcp

This client is separate from any AI client's native MCP surface. For Codex CLI, it demonstrates a reproducible agent-driven SDK workaround: if the agent has shell, Node.js, local dependency, and localhost network access, it can run this client to call resources/subscribe, receive notifications/resources/updated, and re-read the updated resource.

Verification Procedure

Use docs/verification-guide.md for a repeatable client verification procedure.

Record results in results/compatibility-matrix.md.

Skill Templates

Reusable Codex skill templates are tracked under docs/skills. The pr-review-subscribe template documents a PR review cycle that uses MCP resources/subscribe as the primary wait route and polling only as fallback.

Client Compatibility

See results/compatibility-matrix-v2.md for the current Round 2 compatibility matrix (tool + resource testing) across Codex CLI, Gemini CLI, OpenCode, GitHub Copilot CLI, Claude Code, Goose, and Crush.