Message counting

How Ably counts messages

As a general rule, most operations involve publishing and receiving messages. Each operation generates:

• 1 inbound message when a client publishes or performs an operation
• 1 outbound message for each subscriber that receives it

For example, if 1 client publishes a message to a channel with 10 subscribers, this counts as 11 messages (1 inbound + 10 outbound).

By default, echo messages are enabled, which means the publisher also receives its own message as an outbound delivery. In the example above, echo adds 1 outbound message for a total of 12 messages.

Client-side message filtering, where a subscribe callback selectively processes messages, does not reduce your message count. Ably delivers all messages on a channel to every subscriber regardless of client-side filtering. To filter messages server-side and reduce outbound message counts, use subscription filters.

The tables below list all operations that count as messages. Unless noted otherwise, each operation follows this inbound/outbound pattern. Time and Ping operations are not counted.

Message size

Ably calculates message size as the sum of the name, clientId, data, and extras properties before any compression or expansion occurs in the serialization process. This applies to all products built on Pub/Sub, including Chat.

• name and clientId are calculated as the size in bytes of their UTF-8 representation.
• data is calculated as the size in bytes if it is binary, or its UTF-8 byte length if it is a string.
• extras is calculated as the string length of its JSON representation.

Ably bills messages in 5KiB chunks. A message up to 5KiB counts as 1 message. A 50KiB message counts as 10 messages, and a 16KiB message counts as 4 messages.

Each package has a bandwidth allowance based on an average message size of 5KiB. If your total bandwidth for the month exceeds this baseline, Ably charges overage per GiB. See maximum message size for the size limits per package type.

Pub/Sub operations

The following table shows how Pub/Sub operations contribute to your message count:

For Pub/Sub-specific cost optimization strategies, see Pub/Sub pricing.

Chat operations

The Chat SDK is built on top of Pub/Sub. All Chat operations generate Pub/Sub messages that follow the same counting rules.

For Chat-specific cost optimization strategies, see Chat pricing.

LiveObjects operations

LiveObjects operations are billed using ObjectMessages. Each ObjectMessage follows the standard inbound/outbound counting pattern.

Nested object creation generates additional messages for each nested object.

For LiveObjects-specific cost optimization strategies, see LiveObjects pricing.

Spaces operations

The Spaces SDK is built on top of Pub/Sub channels and presence. All Spaces operations generate Pub/Sub messages that follow the same counting rules.

Live cursors use a separate channel from other space features due to their high update frequency. Registering multiple subscription listeners for the same event does not increase your message count, as these are client-side filtered events.

For Spaces-specific cost optimization strategies, see Spaces pricing.

LiveSync operations

LiveSync publishes database changes as Pub/Sub messages. Each update follows the standard inbound/outbound counting pattern.

For example, if the database connector publishes 1 update and 3 clients are subscribed, this counts as 4 messages (1 inbound + 3 outbound).

For LiveSync-specific cost optimization strategies, see LiveSync pricing.