Claude can request a notification through a tool, but your application—not Claude—must authorize the request, publish the event to Amazon SNS FIFO, and handle the result. For ordered queue processing, subscribe an Amazon SQS FIFO queue. Choose a message group ID that represents the entity whose events must stay in sequence, and make consumers safe to retry.
How the notification flow works
Claude tool use is a request-and-response protocol. Your application declares a tool with an input schema, sends the conversation to the Messages API, and receives an assistant tool_use block when Claude requests the operation. The block identifies the tool and supplies structured input; it does not execute your application code or publish to AWS.
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- Declare a notification tool. Give it a narrow purpose, such as requesting an order-status notification, and define the accepted input fields with a schema.
- Inspect Claude’s response. When the response has
stop_reason: tool_use, read the tool-use block and its ID. Do not treat the requested input as authorized merely because it is well-formed. - Validate and authorize in your application. Check the caller’s permissions, the target entity, allowed notification type, and business rules. Reject or safely handle fields the tool is not permitted to control.
- Create and publish an event. Build a notification event with a stable business identifier, then publish it to an SNS FIFO topic with a message group ID and a deduplication ID—or use content-based deduplication deliberately.
- Return a tool result to Claude. Send a
tool_resultassociated with the matching tool-use ID. Report what your application actually knows, such as that the event was accepted for publication; do not claim that every subscriber received or processed it unless you have evidence. - Process downstream. An SQS FIFO subscriber receives its own ordered stream. Its consumer performs the notification work and records enough state to handle retries safely.
These are separate success boundaries: Claude requested an operation, the application authorized it, SNS accepted a publish, SNS delivered to a subscription, a queue consumer processed the event, and a user-facing notification may have been delivered. Track and report those outcomes separately.
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Choose the ordering key from the business rule
SNS FIFO ordering is scoped to a message group, not the entire topic. Events assigned to the same group are ordered; separate groups can be processed in parallel and have no relative ordering guarantee. Set the group ID to the entity whose events must be serialized.
#1 Best Overall
| Business invariant | Possible message group key | What it serializes |
|---|---|---|
| Messages in one conversation must stay ordered | Conversation identifier | Events for that conversation |
| Account changes must be observed in sequence | Account identifier | Events for that account |
| Steps in one workflow must not overtake each other | Workflow identifier | Events for that workflow |
These keys are examples, not interchangeable defaults. If two conversations for one account must also be ordered against each other, grouping only by conversation does not express that requirement. Conversely, grouping every event under one shared key can unnecessarily serialize unrelated work.
Choose a deduplication strategy
A FIFO publish requires a deduplication ID unless content-based deduplication is enabled. During the five-minute deduplication interval, SNS accepts a repeated deduplication ID but does not deliver the duplicate again. This helps with repeated publish attempts, but it does not replace application-level duplicate handling across the whole processing path.
Rank #2
| Approach | How it identifies a duplicate | Use it when | Important limitation |
|---|---|---|---|
| Explicit deduplication ID | Your application supplies a stable event ID. | You can assign a durable identifier to each logical event and reuse it on retries. | Different logical events need different IDs; retries of the same event should retain its ID. |
| Content-based deduplication | SNS hashes the message body. | The body itself consistently identifies equivalent publish attempts. | Message attributes are not included in the content hash, so differences carried only in attributes do not distinguish messages. |
Use a stable event identifier in the event body as well as for explicit deduplication where appropriate. Consumers should still be designed to handle repeated work safely: AWS’s exactly-once delivery and processing conditions are specific, and depend on factors including an eligible SQS FIFO endpoint, timely message deletion by the consumer, no subscription filtering, and no network disruption.
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For a consumer that needs FIFO queue processing, subscribe an SQS FIFO queue to the SNS FIFO topic. SNS FIFO delivers to subscribed SQS queues in publish order, and a FIFO queue consumer receives that queue’s messages in order. By contrast, a standard SQS subscriber may receive messages out of order and more than once.
Each FIFO queue subscriber preserves its own stream. That does not establish a shared processing order across separate subscribers: their delivery and processing can happen at different times. A subscriber that is unreachable can fall behind. Configure a dead-letter queue on the subscription when failed deliveries must be retained for investigation or recovery rather than dropped.
If a Lambda function processes each event
Use the SQS FIFO queue as the Lambda event source. Do not configure a direct SNS FIFO-to-Lambda trigger: Lambda’s direct SNS trigger supports standard SNS topics only. In this topology, SNS FIFO publishes to SQS FIFO, and the queue invokes the Lambda consumer.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Design the event and tool boundary
Keep Claude’s requested action narrower than the AWS publish operation. Claude can supply intent and allowed business inputs; application code should determine trusted identifiers, authorization context, group ID, deduplication ID, and any fields that must come from authoritative systems.
The Tool Desk
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Best Value
When assembling the tool result, distinguish failure to validate, failure to publish, and successful SNS acceptance. If publication succeeds but a consumer later fails, that later outcome belongs to the delivery and processing path; it should not be presented as completed notification delivery to Claude without corresponding status evidence.
Plan for failures at each boundary
- Tool request: Claude may omit a required field or request an operation that is not permitted. Validate the schema and business policy before acting.
- Application execution: A crash after the side effect but before recording success can lead to a retry. Use stable event identity and duplicate-safe processing.
- SNS publish: Record whether the publish was accepted, and retain enough event context to diagnose or retry an uncertain outcome without silently creating a new logical event.
- SNS-to-SQS delivery: Monitor delivery failures and configure subscription dead-letter handling if failed delivery must be recoverable.
- Queue processing: Track receive, processing, and deletion outcomes. A consumer should not delete a message before its required work has succeeded.
- Final notification: Queue processing is not proof that an email, SMS, or other user-facing destination received the notification. Track that final step separately if it matters to the product.
Apply least-privilege IAM permissions to the application publisher and each consumer, and instrument the distinct stages with event identifiers and status records. Exact IAM policies and retry settings depend on the AWS resources and application behavior; they should be designed for the deployed topology rather than inferred from the FIFO feature alone.
Quick Recap
When this pattern fits—and when it does not
- Use SNS FIFO with SQS FIFO when multiple queue-based consumers need ordered streams within defined message groups.
- Use a standard queue only when best-effort ordering is acceptable; it does not provide the FIFO ordering behavior described here.
- Do not use SNS FIFO as a direct delivery path to email, SMS, mobile app, or customer-managed HTTP/S endpoints. It cannot send directly to those endpoint types.
- Use queue-triggered Lambda when Lambda must process events from the FIFO flow.
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