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Spine

A lightweight, modular, protocol-native runtime for production AI agents.

A tiny, load-bearing kernel — guards, durable state, and observability — that everything else plugs into as opt-in middleware, swappable backends, and protocol adapters.

Get started How it works GitHub 
from spine_core import Agent

agent = Agent("openai:gpt-4o-mini")
result = await agent.run("say hello")
print(result.answer)
No hidden prompts No runaway loops Deterministic replay

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Three guarantees

  • No hidden prompts

    Every model call consumes inspectable, typed Message objects. No prompt is ever constructed outside your view.

  • No runaway loops

    Guards are enforced inside the kernel, every iteration — not bolted on. Step, cost, token, wall-clock, and delegation ceilings are structural.

  • Deterministic replay

    Every step emits a trace event; any run can be recorded and replayed step-for-step without calling the provider or any tool.

What's in the box

Plane Ships with
Kernel step loop, explicit serializable state, guards, tracer, HITL interrupt/resume, parallel tools, cancellation, sub-agents
Middleware retry, fallback, loop guard, structured output, compaction, cost tracking, caching, guardrails (PII/injection/policy), circuit breaker, idempotency, rate limit, deterministic replay, memory recall, tenant budgets, tool timeout/truncation/sandbox
Backends checkpoints (in-memory, SQLite, Redis, Postgres); memory (vector, buffer, pgvector) with pluggable embedders
Providers OpenAI, Anthropic — and any OpenAI-compatible endpoint (Ollama, vLLM, Groq, …). See Models
Adapters MCP (tools), A2A (remote agents), OpenTelemetry (spans)
Tooling CLI (init/run/chat/dev/trace/eval/doctor/plugin), eval harness, orchestration patterns

Why Spine

The integration layer that made monolithic frameworks valuable has been commoditized by open standards (MCP for tools, A2A for agents). The durable value sits in the reliability runtime — the execution loop, guards, durable state, and observability that decide whether an agent survives production. Spine owns that core and lets the standards do the integration.

Get started Read the architecture