Debugging with Ably CLI

The Ably CLI (@ably/cli, install via npm install -g @ably/cli) lets you observe, test, and simulate Ably operations from the terminal — faster than console.log or browser DevTools.

Discovering commands: Run ably --help for command groups, ably <command> --help for subcommands, flags, and examples. The CLI is self-documenting. This skill teaches what's possible and when to use it.

1. Diagnostic Decision Tree

Messages not arriving
├── Is anyone on the channel?        → list channels with a prefix filter
├── Was anything published?          → check channel history (2 min only without persistence)
├── Can I see messages live?         → subscribe to the channel
├── Test round-trip                  → subscribe in background, publish from main terminal
└── Check channel lifecycle          → subscribe to channel lifecycle logs, or inspect the channel in the dashboard

Presence not working
├── Who is actually present?         → subscribe to presence on the channel
├── Simulate a client joining        → enter presence with custom client-id and data
├── Check presence member count      → get channel occupancy
│   (stale members? ungraceful disconnects take ~15s to be removed)
└── Watch all presence events        → subscribe to logs filtered by channel.presence, or inspect the channel in the dashboard

Connection problems
├── Can I connect at all?            → test connection (try ws and xhr separately)
├── Is Ably up?                      → check service status
├── Watch connection lifecycle       → subscribe to connection lifecycle logs
└── Connection count vs plan limit   → check app stats in live mode

Auth errors
├── Is the API key valid?            → test connection with the specific key
├── What capabilities does key have? → list auth keys
├── Using tokens (JWT or Ably)?      → issue a test token via CLI to verify the key can create valid tokens
│   (CLI token issuance tests the key, not your app's authUrl/authCallback)
├── Token expired (40142)?           → check TTL and renewal config (authUrl/authCallback)
└── Look up the error code           → ask the support agent or fetch help.ably.io/error/{code}

Channel state / lifecycle issues
├── Watch channel events             → subscribe to channel lifecycle logs
├── Watch all app meta events        → subscribe to all logs
├── Check channel occupancy          → get or subscribe to occupancy
└── Check channel rules/config       → list channel rules (persistence, TLS, push, etc.)

Push notifications not working
├── Watch push delivery logs         → subscribe to push logs (meta channel)
├── Check push log history           → get push log history
├── Is push enabled on namespace?    → list channel rules, check push-enabled
└── Check integration rules          → list integrations, check source type and channel filter

Integration rules not firing
├── List all integrations            → list integrations to see rules, source types, status
├── Check source type matches        → source can be channel.message, channel.presence,
│                                      channel.lifecycle, or presence.message
├── Check channel filter             → filter pattern must match the channel name
├── Is the rule enabled?             → check integration status (enabled/disabled)
└── Check for delivery errors        → check log history — the log metachannel captures
                                       errors sending on integrations

Queue issues
├── Are queues configured?           → list queues
├── Is the integration routing to it?→ list integrations, check AMQP rule target
└── Check message flow               → subscribe to the source channel to verify messages exist

Chat room issues (@ably/chat)
├── Are messages flowing?            → subscribe to room messages
│   (if CLI sees messages but app doesn't → room.attach() likely missing)
├── Check room presence              → subscribe to room presence
├── Check occupancy                  → get room occupancy
├── Check underlying channel events  → inspect the room's channels in the dashboard, or subscribe to channel lifecycle logs and look for the room's channel names
└── Send a test message              → send a message to the room from CLI

Spaces issues (@ably/spaces)
├── Who is in the space?             → subscribe to space members
├── Watch cursors                    → subscribe to space cursors
├── Watch locations                  → subscribe to space locations
└── Check locks                      → get all locks in the space

2. Key Debugging Facts

Channel names are case-sensitive. Mismatched names between publisher and subscriber is a common bug. List active channels to see what actually exists.
History defaults to 2 minutes. Without persistence, history only covers Ably's connection recovery window. Check channel rules for persisted: true. If not enabled, tell the user and suggest enabling via channel rules or the dashboard.
Presence requires clientId AND capability. The clientId must be set at connection time (not per-presence-enter). Entering presence requires the presence capability; subscribing to presence events requires subscribe capability. A client can observe who's present without entering itself. Without the right capability, presence operations fail with 40160.
Capability scope on channel names. A key with publish:["chat:*"] allows publish on channels starting with chat: (e.g., chat:room-1), but NOT on a channel literally named chat. The colon separator and wildcard pattern matter — this is a common cause of 40160 errors.
Token expiry (40142). Tokens have a TTL. If the client has no authUrl or authCallback configured for renewal, the token expires; any connection will fail and any other API requests will be refused. Test token issuance via the CLI to verify auth flow works independently of the app.
Presence removal delay. Ungraceful disconnects take ~15 seconds to be removed by Ably.
Occupancy reveals duplicate subscriptions. If subscriber count is much higher than expected, check for duplicate subscriptions (React StrictMode, missing useEffect cleanup, multiple Ably client instances).
Token vs key capabilities. Keys and tokens issued from them can have different capabilities; the rights of a token is the intersection between the rights of the key, and the specific rights specified in the token. Debug 40160 errors by checking both the key capabilities AND the token creation code on the server.
Metachannel logs require [meta]* capability. All ably logs commands subscribe to logs metachannels ([meta]log, [meta]channel.lifecycle, etc.). A key scoped to * does not match metachannels — the key needs [meta]* or [*]* in its capability resource list. The app's root API key has [*]* by default. If ably logs commands fail with 40160, check the key's capability scope. For deep inspection of a single channel (per-channel stats, regional breakdown, attached integrations), use ably channels inspect <channel> to open the dashboard's channel inspector — this uses privileged inspection metachannels ([meta]inspect:*) not currently available to the CLI.
Transport fallback. If WebSocket is blocked, the SDK falls back to XHR streaming. Test both transports separately to confirm which works.
Non-default environments. If the app uses a sandbox or custom environment, log in with ably accounts login --endpoint <host> to target the right cluster.
Error message text > error code. Ably error codes are broad categories (e.g., 40000 covers many variants). Always read the error message text for the specific cause. Every code has a help page at help.ably.io/error/{code}, or use ably support ask "error {code}".

3. CLI Authentication

The CLI needs credentials. Two approaches:

Credentials from the project (quick, no login): Set ABLY_API_KEY as an environment variable. Find the key from the project's environment files and export it (e.g. export ABLY_API_KEY=...). Alternatively, if you have a token (e.g., from the app's auth server), use ABLY_TOKEN instead. If the key is for a production app, note this to the user before using it.

Log in to the CLI (for extended debugging or account-level commands): ably login opens a browser for OAuth. Once logged in, use ably apps list and ably apps switch to target the right app, and ably auth keys list to see available keys and their capabilities.

If no credentials are available, ask the user: "I need Ably credentials to debug this. Can you share the API key from your .env, or run ably login?"

4. What the CLI Can Do

Observe (Read-Only)

Subscribe to channels, presence, occupancy, logs, and stats in real time — you see exactly what Ably sees.

Channel messages: Subscribe to one or more channels. Supports wildcards and rewind (replay recent messages on attach).
Presence: Watch who enters and leaves, with their client IDs and data payloads.
Occupancy: Snapshot or live stream of publishers, subscribers, and presence members on a channel.
Logs (meta channels): Channel lifecycle, connection lifecycle, presence events, and push notification delivery logs. Filter by type (channel.lifecycle, channel.occupancy, channel.presence, connection.lifecycle, push.publish), rewind to catch recent events.
Push notification logs: Dedicated push log stream and history — see delivery attempts, failures, and device targeting.
History: Past messages on a channel (2 minutes without persistence — see Key Debugging Facts).
Stats: App or account statistics with a live polling mode. Check connection counts against plan limits.
Channel list: Currently active channels with prefix filtering.
Connection test: Verify connectivity across transports (WebSocket, XHR) to isolate network or proxy issues.

Simulate

Act as a participant — simulate one end of a conversation to test the other (client when debugging server, server when debugging client).

Publish: Send messages with event names, JSON, or plain text. Publish repeatedly with configurable count and delay to simulate traffic.
Batch publish: Publish to multiple channels in a single request.
Presence enter: Join a channel with custom client ID and data (e.g., {"role": "server"}).
Chat: Full room simulation — messages, presence, typing, reactions.
Spaces: Members, cursors, locations, locks.
Benchmarking: Publisher/subscriber throughput and latency testing with configurable rates and message sizes.

Manage

Query and modify app configuration to diagnose config-related issues.

Channel rules (namespaces): Check and configure persistence, push, TLS-only, batching, conflation, and channel registry settings.
API keys: List capabilities, create, revoke, switch active key.
Token issuance: Issue JWTs (or Ably tokens if the app uses these) to test auth flows in isolation. Also revoke tokens.
Apps: List, create, switch, configure.
Integrations: List and inspect integration rules — webhooks, Lambda, Kafka, AMQP, and others. Check source types (channel.message, channel.presence, channel.lifecycle, presence.message), channel filters, and enabled/disabled status.
Queues: List, create, and delete Ably message queues.

Get Help

AI support agent (powered by Inkeep): ably support ask "your question" — searches Ably docs and FAQs. Use --continue for follow-ups.
Service status: ably status checks platform health.

5. Long-Running Commands

Many commands (subscribe, presence enter, stats --live, occupancy subscribe) are long-running — they stream output until Ctrl+C or --duration N expires. Run these as background tasks so they don't block your workflow. Start a subscribe in the background, reproduce the issue, then check the output.

6. Connection and Channel State Reference

Connection States

State	Meaning	Diagnostic
`connecting`	Attempting connection	Normal on startup; if stuck, check network/auth
`connected`	Active WebSocket	Healthy
`disconnected`	Temporary loss, SDK retries	Transient is normal; recurring = network issues → watch connection lifecycle logs
`suspended`	Offline >2 min, less frequent retries	Test connection to check connectivity
`failed`	Permanent failure, SDK won't retry	Almost always auth — test with the specific API key
`closed`	Explicitly closed by code	Search for `.close()` calls

Channel States

State	Meaning	Diagnostic
`initialized`	Channel object created, not yet attached	Normal before first subscribe/publish
`attaching`	Requesting attach from server	If stuck, check connection state and auth capabilities
`attached`	Active — messages flowing	Healthy
`detaching`	Requesting detach	Normal during cleanup
`detached`	Not attached, no messages flowing	Check if `detach()` was called intentionally
`suspended`	Attach failed, will retry	Usually follows connection suspension — check connection state first
`failed`	Permanent channel failure	Often capability denied (40160) or invalid channel name

7. Environment-Specific Gotchas

Environment	Symptom	Root Cause	Diagnostic
Next.js SSR	Connection fails during render	No WebSocket in server-side render	Guard with `typeof window` or `useEffect`
Serverless (Lambda, Edge)	Stale/frozen connections	Connection frozen between invocations	Use `Ably.Rest` server-side
React StrictMode	Duplicate messages, presence flicker	Double-render duplicates subscriptions	Check occupancy — much higher than expected = duplicates
CSP headers	WebSocket blocked	Ably domains not in `connect-src`	Test connection — ws fails, xhr works = CSP
Corporate proxy	WebSocket fails silently	Proxy blocking upgrade	Test connection — ws fails, xhr works = proxy
Mobile background	Messages missed after resume	OS kills WebSocket	Check channel history for messages sent during gap

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