Just-MCP pattern enhances spec-driven development for agents (brianhorakh.medium.com)

just-mcp is a Rust-built pattern and companion server that integrates the just command runner (justfile) with LLM agents to enable low‑context, memoized command execution for spec-driven development. Instead of having an LLM ingest whole build scripts, agents can query the runtime with just -l to list parameterized commands (build, test, release, commit) and execute them directly; results and learned fixes are then memoized back into the justfile (a versioned, runnable “tribal knowledge” artifact). The project ships as a multi‑arch binary and Docker image (can be embedded via a multi-stage Dockerfile), with additional runtimes like npx and editor integrations (GitHub Actions, VSCode LSP). This matters because it dramatically reduces token/context waste and surface area for LLMs while improving reproducibility and CI/CD automation: agents operate on abstract, persistent specs rather than raw files, sandbox commands in containers, and persist fixes in Git-controlled justfiles. Technically, just-mcp acts as an MCP-style sub-agent mediating command listing, execution and memoization, enabling iterative agent workflows with minimal context overhead and durable command semantics — a practical pattern for scaling spec-driven agent development and preserving automation knowledge across runs.