Ironmcp

A mistyped argument name should not get a confident answer to the wrong question. ironmcp makes an MCP tool refuse the undeclared argument with a recoverable error and enforce exactly the arguments it advertises — one guarantee, proven by a single conformance corpus, in Python, TypeScript, PHP, and Dart.

Most MCP SDKs validate a tool call against its declared parameters and silently drop any argument that was not declared. One added letter (project → projects) yields a confident answer to a question nobody asked, with no way for the caller to learn their constraint was ignored. ironmcp makes the server refuse the unknown argument with a bounded, recoverable message, and advertise exactly what it enforces on every tool.

The contract lives in spec/ and is executable as the language-neutral corpus in conformance/. Each language kit implements that one contract natively on its own MCP SDK and passes that one corpus — the way POSIX is a single specification with a conformance suite and many native libraries, not one library ported everywhere.

Before and after

# Without ironmcp: search({"query": "x", "projet": "typo"}) drops `projet`, runs search("x"),
# and returns a confident wrong answer.
from ironmcp import strict_server
app = strict_server(name="search", version="1.0.0")
# With ironmcp the same call is refused:
#   unknown argument(s): projet. Tool 'search' accepts: query. Nothing was executed ...

More than the guard

The guard is the core, but every kit ships the same substrate from one dependency: a self-discovery registry (enumerate every live ironmcp server; the registry file is byte-identical across all four languages, so a Python server and a Dart server appear in the same list), a structured readiness/health contract, hardened serving (bearer + open /healthz + a DNS-rebinding host guard on by default), and content + clean-quit helpers. ironmcp is a layer that works with whatever MCP framework you already use — it does not replace it.

Read next

• AGENTS.md — the fast path for an AI agent: harden, serve, and prove conformance in copy-paste blocks.
• ROADMAP.md — the kits, what has landed, what is next.
• CONTRIBUTING.md — how to contribute, including the recipe for adding a language kit.
• spec/strict-args.md — the rule and the refusal message.
• conformance/ — the corpus that makes "same guarantee, every language" provable.

Kits

Kit	Package	Registry	Location
Python	ironmcp	PyPI	kits/python/
TypeScript	ironmcp	npm	kits/typescript/
PHP	ironmcp/core	Packagist	kits/php/
Dart	ironmcp	pub.dev	kits/dart/

A kit conforms when a server built with its strict layer passes every case in conformance/cases/ — and every kit also proves the bare server is refused, because a corpus never watched to FAIL is theatre. ironmcp runs in a production desktop application's live MCP server on both Linux and Windows, hardening 60+ tools with zero behaviour change. See ROADMAP.md for what is next.

Harden, deploy, prove

from ironmcp import strict_server, serve_http, aassert_enforces_v2
app = strict_server(name="search", version="1.0.0")     # refuse unknown args, advertise closed
serve_http(app, token="<secret>", port=8080)            # bearer-guarded /mcp + open /healthz
await aassert_enforces_v2(app)                           # prove every tool: advertise == runtime

The TypeScript kit mirrors this (strictServer / serveHttp / assertEnforces); see kits/typescript/README.md.

Layout

spec/                 the contract (language-agnostic)
conformance/cases/    the corpus (one, owned by no language)
kits/<language>/      one native kit per language, each passing the corpus