This is the heart of agent action. A REPL — read, evaluate, print, loop — is the running core where an agent actually <strong>thinks, acts, and reacts</strong> in real time. Custom platforms don't need one; they just follow a script. But the moment you want a system that runs semi- or fully autonomously, it needs a REPL at its center. <strong>A Jaeger is the larger machine; the REPLs are the coding structures living and working inside it.</strong> This tier builds and wires that core — the ecosystems, tools, and loops an agent runs on.
- **The engine, not the shell** — A platform is the body; the REPL is the beating heart. This is what lets a system act instead of just sit there.
- **Required for autonomy** — You can build a custom platform without one — but no REPL, no Co-Pilot, no Jaeger. This is the prerequisite for everything self-running.
- **Tools an agent can wield** — We build the ecosystem of tools, functions, and routines the agent reaches for inside the loop — its hands, not just its brain.
- **Built to live inside a Jaeger** — Structured so this core drops straight into a larger autonomous system when you scale up to Tier 1 or 2.
| Agent REPL core | The read-eval-print-loop runtime an agent thinks and acts inside | $8K – $30K |
| Tool ecosystem | The functions, routines, and integrations the agent wields inside the loop | $4K – $18K |
| Orchestration layer | Wiring multiple loops and tools into a coherent, controllable core | $6K – $20K |
| Retainer | Tuning, expanding the toolset, and hardening the core over time | $1K – $4K/mo |
**Do I need this if I just want a custom platform?**
No. Deterministic platforms (Tier 4) run fine without a REPL. You need this the moment you want a system that decides and acts on its own.
**What actually gets built here?**
The execution loop and the tools around it — the runtime where the agent reads input, evaluates, acts through its tools, and loops. Plus the ecosystem it operates in.
**How does this relate to a Jaeger?**
The Jaeger is the whole autonomous operation. The REPL is the core inside it doing the live thinking and acting. You can't have the former without the latter.
*This is the substrate autonomous systems are built on. Often the first thing built before commissioning a Tier 1 or 2 Jaeger.*