Transport-level routing for MCP/ACP protocols
stdio Bus
Deterministic stdio-based kernel in C providing transport-level routing for ACP/MCP-style agent protocols. stdio Bus acts as a process supervisor and message router, handling NDJSON-framed JSON-RPC messages with session-based routing while remaining completely agnostic to protocol semantics.
Stack Position
stdio Bus operates as a transport layer between external clients (IDEs, CLIs, services) and worker processes. It receives connections via stdio, Unix sockets, or TCP, routes messages to appropriate workers based on session affinity, and returns responses to the originating client. stdio Bus does not interpret message content—it treats all payloads as opaque JSON-RPC envelopes.
Architecture
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Key Characteristics
Zero AI Logic
stdio Bus contains no AI, LLM, or inference code. It routes messages without interpreting their semantic content.
Single-Threaded
Event-driven architecture using epoll (Linux) or kqueue (macOS). No threading complexity.
No External Dependencies
Pure C11 implementation with only libc. No runtime dependencies to manage.
Protocol Agnostic
Routes JSON-RPC messages without understanding MCP, ACP, or any specific protocol semantics.
Session Affinity
Maintains client-to-worker session bindings for stateful interactions.
Backpressure Management
Handles flow control between fast clients and slow workers without message loss.
Documentation
stdio Bus is the reference implementation of the protocol standard. This specification and implementation are maintained at stdiobus.com.