Observed Signal · Aug 30, 2026 · Technical Release · Source: DEV Community · Impact: 2/5 · Sentiment: Positive
Autonomous agents / Exactly-once execution Market: Exactly-once Python library prevents duplicate payments
exactly-once is an open-source Python library that guarantees a side effect (for example, paying an invoice) executes at most once per key and replays the stored result on subsequent calls. It provides a @once decorator / context manager, stores with different atomicity guarantees (memory, SQLite, Redis, Postgres SERIALIZABLE), crash quarantine with probers and worker leases, passthrough of provider idempotency keys via current_key(), an onchain adapter keyed by nonce, and wrappers for integrations such as LangGraph nodes and CrewAI tool runs. The project is available on GitHub under MIT and can be installed via pip.
An open-source library that improves reliability and idempotency of autonomous agents and transactional side effects; useful to developers building agentic systems but not industry-shifting.
Key Takeaways & Evidence Grounding
- exactly-once is an open-source Python library that enforces at-most-once execution of side effects per key.
- The library implements a three-state lifecycle for keys: FRESH → IN_FLIGHT → COMMITTED.
- Stores provided include memory, SQLite, Redis, and Postgres (SERIALIZABLE), each with documented atomicity guarantees.
- The project includes probers for crash quarantine recovery, an onchain adapter keyed by transaction nonce, and wrappers for LangGraph and CrewAI.
- The code repository is available at github.com/swarmproof/exactly-once and is released under the MIT license.
Connected Companies & Entities
4 Entities mappedLangChain
Agent engineering software for building and operating AI agents.
CrewAI
Enterprise platform for building and operating multi-agent AI workflows.
“Wrappers for LangGraph nodes and CrewAI tool runs, and any plain function, loop, or worker....”
Stripe
Financial infrastructure platform for payments, billing, fraud, and commerce operations.
“Further reading: [Stripe on idempotency]...”
Amazon Web Services (AWS)
Cloud infrastructure, platform and AI services for enterprises and developers.
“Further reading: [AWS Lambda Powertools idempotency utility]...”
Ontology Mapping & Concepts
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