Iii
Compose distributed services as easily as importing a library.
If you're tired of wiring microservices and want a single, observable runtime for polyglot agents, iii is worth a deep look. But it's early—v0.11.x—and requires self-hosting, so skip it if you need a managed offering or no-code integrations.
- Backend engineers tired of wiring microservices together
- Agent builders who want a unified runtime instead of multiple harnesses
- Platform teams shipping internal capabilities as workers
- Startups needing fast iteration without vendor lock-in
- Teams looking for a managed cloud platform (iii is self-hosted / local-first)
- Users who prefer graphical configuration over code-defined primitives
- Projects needing no-code integration flows
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In short
Iii — Compose distributed services as easily as importing a library. Best for Backend engineers tired of wiring microservices together, Agent builders who want a unified runtime instead of multiple harnesses, Platform teams shipping internal capabilities as workers. Free to use.
What's new in Iii
Checked 14 days agoAcross the latest 8 updates: 3 feature updates, 3 launches, 1 changelog entry and 1 news mention.
Loop Engineering Is Just Software Engineering. We Have a Name for That.
iii describes loop engineering as event-driven distributed systems with retries and dead-letter handling, shipped as one worker.
iii 0.20.0: Major SDK reorganization and shared types extraction
Node, Python, Rust SDKs reorganized; shared types moved to @iii-dev/helpers; cross-language API aligned.
How to Build Your Own Agent Harness
iii decomposes agent harness into eleven independently-replaceable workers on one engine bus.
The Substrate Is Installable
iii provides the surrounding layer for agents (task state, event logs, etc.) in three commands.
Why agent sandboxes are converging on libkrun, not Firecracker
iii explains libkrun as practical microVM path for local-first coding agents.
Building Agents for Real World
iii argues validation, isolation, and observability should be runtime properties.
Add a worker
iii presents three primitives and one engine to handle agent complexity.
The Harness Is the Backend
iii makes the agent harness the backend, not a separate world.
Viability Score
How likely is Iii to still be operational in 12 months? Based on 4 signals — momentum (how recently it shipped), wrapper dependency, revenue model, and web presence.
Last calculated: July 2026
How we score →Key Features
- Three primitives: Worker, Trigger, Function
- Polyglot workers: Node.js, Rust, Python, Go
- Unified observability console with logs, traces, streams, queues, state
- One-command worker registry: `iii worker add`
- Cross-language function calls
- Runs anywhere: Docker, Kubernetes, edge, browser, Raspberry Pi, microVM (libkrun)
- Durable state, retries, dead-letter handling
- Built-in agent support: agents as workers
- Event-driven loops and cron triggers
- WebSocket, HTTP, and event triggers
- Key-value state store with namespacing
- Streaming observability via WebSocket
- Open-source, locally installable (v0.11.x)
- SDKs with shared protocol for Node.js, Rust, Python, Go
- No integration cost: add a worker instead of procuring tools
About Iii
iii is an open-source runtime that collapses service composition into three primitives—Worker, Trigger, and Function—eliminating the quadratic complexity of integrating cloud tools. Backend engineers, agent builders, and platform teams use iii to add capabilities like queues, cron, streaming, and observability with a single command: `iii worker add <name>`. Workers can be written in any language (Node.js, Rust, Python, Go) and deployed anywhere: Docker, Kubernetes, edge, browser, Raspberry Pi, or microVM (libkrun). The iii engine handles serialization, routing, durable state, retries, and dead-letter handling across all workers, surfaced in a unified console with live logs, traces, streams, and state. Agents are first-class citizens—they're just workers with access to every function, trigger, and state in the system, removing the need for separate agent harnesses. The platform is local-first and installable in three commands, with a growing worker registry that ships integrations like npm packages. While not a managed cloud service, iii's open-source core and polyglot SDKs make it a radical alternative to traditional service meshes and integration platforms, especially for teams that want to iterate fast without vendor lock-in.
Behind the Verdict
iii's premise is bold: reduce all service composition to three primitives and make every capability a plug-in worker. It's refreshingly opinionated—no Kubernetes CRDs, no YAML configs, just code. The unified console gives you real-time visibility into workers, functions, triggers, and state across languages, which is a huge productivity win for teams building agentic systems. We'd reach for this when we want to stop gluing together queues, cron, and observability tools and instead let the runtime handle the boilerplate. The 'agents are just workers' philosophy is elegant—you avoid the fragmentation of agent frameworks and keep everything debuggable from one trace. That said, iii is still maturing. The version on the site is v0.11.3 (though the profile mentions v0.20.x—news trumps, so current is v0.11.x), and there's no managed cloud tier, so operations are on you. The libkrun microVM path is smart for local-first code agents, but it adds complexity on macOS/Windows. Compared to Temporal or Dapr, iii is more opinionated and simpler to start, but lacks the battle-tested ecosystem and enterprise certifications. Where it bites: you're trading integration flexibility for a framework you must fully adopt. If you need SOC2 or HIPAA out of the box, or if your team prefers GUI configuration, look elsewhere. For polyglot backend teams or agent builders comfortable with self-hosting and rapid iteration, iii is a genuine alternative to the status quo.
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Use Cases
- Compose a real-time data pipeline by chaining a Python ML worker and a Rust transform worker
- Add a sandboxed code execution worker to an agent harness with one command
- Replace a message queue with a worker that handles retries and dead-letter logic
- Monitor all services from a unified console showing logs, traces, and state
- Build a multi-step approval workflow with triggers and durable state workers
- Deploy the same worker locally and in production without rewriting
Limitations
- No hosted cloud plan; users must self-host or run locally.
- The registry is community-driven and still growing—not all integrations are available.
- Documentation is thorough but assumes intermediate systems knowledge; beginners may find the primitives abstract.
12-month cost
Project the real annual outlay, including the implied monthly cost when only an annual tier is published.
Vendor list price only. Add-on usage, seat overages, and contract minimums are surfaced under Hidden costs & gotchas.
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