interjson-moonbit (Python)

InterJSON is the execution gate for LLM output: it decides whether a model's JSON may be executed, and when it may not, returns the sentence to send back to the model. This distribution is the Python client for the MoonBit engine — streaming repair, partial parsing, and the gate — plus two console scripts, one of which starts the local MCP server.

No third-party dependencies and nothing else to install: the wheel carries the engine for every platform the project releases — Linux x86_64 and arm64, macOS arm64, Windows x86_64 — and picks the right one at import time. The engine is the same native binary the CLI ships, reached over a versioned stdio protocol.

pip install interjson-moonbit

The distribution name is interjson-moonbit on PyPI (the suffix identifies the MoonBit engine); the import name is interjson. Version 1.5.1 was published to PyPI on 2026-10-30. The npm package is published too: npm install interjson-moonbit.

An engine that is already installed keeps priority: INTERJSON_BIN, then interjson on PATH, then the bundled binary. Set either to point the client at a newer CLI than the one this wheel was built with.

import json
from interjson import Client

with Client() as jm:
    plan = jm.analyze(
        model_output,
        profile="agent",
        schema_json=tool["inputSchema"],  # the declaration you already have
    )
    if plan["executable"]:
        args = json.loads(plan["text"])
    else:
        print(plan["retry"]["prompt"])    # feed this back to the model

Client keeps one interjson serve process alive, so a loop pays the spawn cost once. repair, analyze and validate are one-shot convenience functions that spawn a process per call.

Console scripts

interjson-mcp is a launcher, not a server: it resolves the engine and replaces itself with <binary> mcp, so stdin/stdout stay a clean JSON-RPC channel with no Python in the middle. Resolution order is INTERJSON_BIN, then interjson on PATH, then the binary this wheel carries for the current platform. Only a platform the release does not build for — Intel macOS, for example — needs INTERJSON_BIN.

interjson --version                  # interjson 1.5.1: the engine the launchers need
interjson-mcp                        # MCP stdio server
interjson-mcp --print-config=claude  # the client configuration snippet
interjson-http --port 8080           # POST /repair /analyze /validate /readiness, GET /healthz

pip install installs the client, the two console scripts and the engine. Nothing has to be on PATH for the configuration below to work:

With the engine resolvable, the client configuration is one line:

{
  "mcpServers": {
    "interjson": { "command": "interjson-mcp" }
  }
}

The server exposes four read-only tools: interjson_gate (the gate: executable, decision, exactness, value, retry.prompt), interjson_repair, interjson_validate, and interjson_readiness. The gate defaults to the agent profile, which equals Options::for_agent() — prose before the arguments is skipped rather than refused. A refused result always carries a non-empty retry.prompt and value: null. MCP is advisory: the model can decline to call the gate, so the host must gate the call itself (a Claude Code PreToolUse hook or a host-SDK gate() — see docs/INTEGRATIONS.md).

Deployment, per-client configuration, the privacy model and troubleshooting are in docs/MCP.md; host-side recipes (LangChain, LlamaIndex, streaming) are in docs/INTEGRATIONS.md.

interjson-http is stateless: one engine process per request, closed after it. It is the path for n8n, Dify, Coze or a gateway; for throughput, use Client.

Methods

profile is one of permissive, interactive, execution, agent, strict. execution and agent refuse a lossy or ambiguous repair instead of inventing content; InterJSONError carries code, message, exit_code, retry_hint and offset.

schema is the library's declaration language ({!query:string,!limit:integer}). schema_json is a JSON Schema subset — type, properties, required, items, enum, const, minimum, maximum, exclusiveMinimum, exclusiveMaximum, minLength, maxLength, pattern — so a tool's existing inputSchema can be passed directly. Unsupported keywords raise E070 rather than being silently dropped.

Version

The Python package is 1.5.1, the engine version, published to PyPI on 2026-10-30. The MoonBit package on mooncakes is 0.13.0 because the registry currently accepts only 0.x.y; the bytes are the same. Client.hello() reports both. 0.13.0 was published on 2026-10-29, and 0.12.0 (the 1.5.0 correspondence) on 2026-10-28.

License: Apache-2.0.