jdBasic

Why it's ranked here

Few MCP servers give an agent a live, stateful runtime instead of a fresh process per call, and this one documents exactly how it does it: one shared VM across every tool call, a 30-second default watchdog that parks runaway code without wedging the session, and a documentation lookup tool meant to stop models inventing builtins that do not exist. MIT licensed, with a CI workflow, a browser playground and prebuilt release binaries. The catch is scope. This is one author's language, so an agent gains a live runtime only for programs written in jdBasic.

What's good

The agent integration is specific rather than decorative. Fourteen documented tools cover running code, linting without running, listing variables and functions, saving and restoring workspaces, and pausing and resuming a running script, and the pause and status calls answer even while another call is busy. The build is modular: the minimal binary is just the VM and standard library, and the MCP-ready Core release is about 8 MB with no LLVM needed. The language reference is candid about its own traps, explaining why comparing a value to NONE misleads and adding a null-coalescing operator so the correct check is the shorter one.

Tradeoffs

Security is the user's job. The MCP tools run arbitrary code with filesystem, shell, network and native function access, and the HTTP transport has no built-in authentication, so the docs say to bind it to localhost. Building from source means hand-downloading SDL3, ImGui, ONNX Runtime and LLVM 18 into an ignored libraries folder, and the runtime library for compiled executables must be rebuilt with identical feature flags or those programs lose builtins. The one CMake file lists five sources and none of the feature flags, so the real build lives in the platform scripts. Forms and COM automation are Windows only.

How to use it well

Best fit: a tinkerer who misses the VB6 habit of editing a program mid-run and now wants an agent doing the edits, especially on small games, GUI tools and data experiments. Grab the Core release, point your MCP client at the binary with the MCP flag, and have the agent look names up with the documentation tool before it evaluates code. Keep the server on stdio or localhost and run it under your own account. It does nothing for code in Python, JavaScript or any other language: live patching only works inside jdBasic programs.

Observed

License

MIT (LICENSE.txt)

Implementation language

C++17 interpreter core; programs and the bundled module library are written in jdBasic

Interfaces

CLI interpreter with REPL, MCP server over stdio and HTTP, DAP debug adapter for VS Code, native compiler to standalone executables

MCP authentication

None built in; the HTTP transport is documented as localhost-only unless fronted by an auth proxy

MCP tool reach

Evaluated code can read and write files, spawn processes, open network connections and call native functions

Build system

Feature-flag build scripts for Windows (MSVC) and Linux; third-party libraries are unpacked manually into a gitignored libs directory

Packaging

Prebuilt GitHub release binaries in Core and Full variants; Full adds LLVM 18 for native compilation

Platform-specific features

Win32 forms and COM automation are Windows only

Authorship

README written in the first person by a single author; copyright held by Computerwelt AI Solutions LLC