Iii

iii is a self-hosted runtime for building distributed backends and agentic systems out of three primitives: Function, Trigger, and Worker. Something hosts work, something causes it, something does it. Rather than assembling a queue, a cron scheduler, a stream processor, a cache, and an observability stack and gluing them together, you add a worker — `compose::add` pulls a declared capability into the running system and makes it immediately callable by every other worker. Workers register over a shared WebSocket protocol (ws://localhost:49134). The vendor's own demos show a TypeScript orchestrator calling a Rust function and a Python function, with results returning over the same connection. TypeScript, Python, and Rust are the SDK languages the site currently lists, so services in different languages call each other natively instead of through sidecars or bridges, and the engine handles serialization and routing underneath. The same worker contract applies whether a workload runs in Docker, on Kubernetes, on the edge, on a laptop, or on your own cloud hardware — moving a workload is a redeploy, not a rewrite. Agents get treated as workers too, which is the part worth attention. Their tools are functions, their session context is state, their orchestration is triggers, and the vendor's demo wires a github worker plus an llm-router plus a provider worker into a PR-digest agent without leaving the runtime. An agent that hits a task outside its current capabilities can register a new worker at runtime and expose new functions. Recent releases push on durability and debugging: iii 0.24.4 cut a 50-trace query from 2098ms to 35ms in vendor benchmarks by paginating unfiltered traces via root-span keys, added `include_events: false` for leaner spans, and 0.24.6 is the version on the install page today. It suits backend engineers, platform teams, and agent builders who are finished procuring a separate service for every new requirement, and polyglot teams running