mklang 0.5.4

A declarative language for LLM-driven state machines (reference interpreter).

mklang

A declarative language for LLM-driven state machines. A .mk file (mk = machine) describes an agent as a set of states; an LLM is the runtime that executes generative steps. The document is the program; the host supplies the interpreter, optional tools, and optional code-hook gates.

mklang : LangGraph  ::  a declarative spec : Python code

The idea

Each state has four faces:

Face	Answers	Example
structure	what shape?	"The output is an email reply, max 150 words"
prompt	what to think?	"Write a reply to {{ticket.body}}…"
execution	how to act?	"Do not invent policies not in the KB facts"
gates	when to exit?	see below

Real side effects (search, send, calc) are tool: states — host callables, not prose in execution. See examples/react.mk and examples/triage.mk.

The output of a state is stored in the shared context under its output: key, so later states read it via {{key}}. Four optional faces unlock richer reasoning: reason (traced chain-of-thought), accumulate (append to a list), fan-out (sample: N / over: {{list}}), and call (run another machine) — see Reasoning architectures.

Gates are the transitions. A state's gates list is its transition table: each gate is a natural-language condition the LLM judges, plus what happens next.

gates:
  - when: the reply resolves the request and is in the required tone
    then: ok
    to: send
  - when: information from the KB is missing
    repair: 2 # re-run this state with feedback, up to 2 times
    to: gather
  - when: the request needs a human
    escalate: true
    to: human_review

Policies: ok (advance), repair(N) (self-correct with feedback), escalate (route to a handler), fail (abort). A global step budget prevents runaway loops.

Design commitments

• Document-first — readable without the interpreter; prose-first for the common path. Production machines still need developer judgment for tools, hooks, and untrusted inputs (see SPEC threat model).
• LLM-as-runtime — non-deterministic by design; gates (prose + optional code hooks + budgets + trace) are the reliability mechanism. Prose-gate accuracy is an empirical claim, not a free lunch.
• Prose, not types — structure and gate conditions are natural language, judged by the LLM at runtime; optional hook: gates add host bool checks.
• Provider-agnostic — a .mk never names a provider or model. States route by capability tier (fast / balanced / reasoning); the runtime maps each tier to a concrete model. Portability of the document is syntactic; whether different providers fire the same gates on the same run is measurable (see scripts/gate_divergence.py).
• Spec + conformance — an implementation-neutral conformance suite pins interpreter semantics so a second runtime can match the language contract.
• Language-agnostic runtime — the spec assumes only "some host with an LLM".

Files

• SPEC.md — the full language specification.
• schema/mklang.schema.json — JSON Schema that validates the structure of a .mk file (add # yaml-language-server: $schema=../schema/mklang.schema.json at the top of a .mk for editor validation).
• config/runtime.example.yaml — host-side runtime config: the tier → model map for each provider (schema).
• src/mklang/ — the reference interpreter (Python, multi-provider).
• docs/ — patterns.md (recommended configs & flows) and adr/ (design decisions); ROADMAP.md.
• examples/ — runnable machines:
  • triage.mk — branching FSM + real search_kb / send_reply tools.
  • research.mk — looping FSM (iterative Q&A).
  • expense_approval.mk — divergent terminals + fail.
  • self_consistency.mk — fan-out sample + reducer.
  • map_reduce.mk + summarize_doc.mk — over + call.
  • react.mk — reason/act/observe loop with accumulate.
  • hook_gates.mk — deterministic code-hook gates (exact policy).

Runtime configuration

The .mk picks a tier; a host-side config picks the model. This is the whole of "make it multi-provider":

active: deepseek # deepseek | anthropic | openai | google | openrouter | xai | mistral | local
providers:
  deepseek:
    base_url: https://api.deepseek.com
    tiers:
      {
        fast: deepseek-chat,
        balanced: deepseek-chat,
        reasoning: deepseek-reasoner,
      }
  anthropic:
    tiers:
      {
        fast: claude-haiku-4-5,
        balanced: claude-sonnet-5,
        reasoning: claude-opus-4-8,
      }
  local:
    base_url: http://localhost:11434/v1
    tiers: { fast: qwen3:8b, balanced: qwen3:32b, reasoning: deepseek-r1:70b }

The example config defaults to DeepSeek (the path we live-test against). Flip active: anthropic (or openai / local / …) and every example runs unchanged. Blocks ship for Anthropic, OpenAI, Google, DeepSeek, OpenRouter, xAI (Grok), Mistral, and local (Ollama/vLLM) — every non-Anthropic one is OpenAI-compatible, so a single adapter serves them all. OpenRouter is a meta-provider: its vendor/model ids let each tier target a different vendor through one endpoint. Per-tier params (Anthropic adaptive-thinking + effort, OpenAI/xAI reasoning_effort, …) live under params. Full map: config/runtime.example.yaml.

Reasoning architectures

Every modern reasoning/agentic pattern maps onto the core (states + gates + prose + tiers + the optional faces). Full skeletons in SPEC.md §10; operating guidance in docs/patterns.md.

Architecture	mklang constructs
Chain-of-Thought	reason: true
ReAct	think → tool state (host callable) → observation accumulated
Reflexion / self-refine	produce → self-judge gate → repair
Self-consistency	sample: N → reducer state (majority)
Tree-of-Thought	sample: k → score/select reducer → loop (depth via budget)
Plan-and-Execute	planner (list) → over: {{steps}} → reducer
Debate / ensemble	over: {{personas}} → synthesizer
Map-Reduce	over: {{chunks}} → reducer
Router-of-experts	classify → call specialists
Speculative cascade	tier: fast draft → escalate → tier: reasoning
Exact policy checks	gate hook: host (ctx, output) -> bool (no LLM)

Install

pip install mklang

Editor validation for .mk files works out of the box via the JSON Schema — point yaml-language-server at https://raw.githubusercontent.com/gianlucamazza/mklang/main/schema/mklang.schema.json.

Quickstart (reference interpreter)

cp .env.example .env            # set DEEPSEEK_API_KEY=… (or another provider key)
uv run mklang check examples/self_consistency.mk
uv run mklang lint examples/self_consistency.mk   # + static analysis
uv run mklang run examples/self_consistency.mk \
  --set question.text="What is the capital of Australia?"
# default provider is deepseek; override with --provider anthropic|openai|…

# pause on budget, resume later (exit code 3 = suspended):
uv run mklang run examples/self_consistency.mk --max-tokens 300 --checkpoint ck.json
uv run mklang resume ck.json --max-tokens 5000

# human-in-the-loop: escalate gates suspend; resume with the human decision:
uv run mklang run examples/expense_approval.mk --checkpoint ck.json --hitl
uv run mklang resume ck.json --set human.reply="approved, cost center 42"

The .mk picks tiers; config/runtime.example.yaml maps them to models (active: deepseek by default); the key comes from .env. Same machine, any provider.

Test your machine without API keys

mklang test runs your machine against a script of named scenarios with a scripted LLM (produce texts, judge picks) and scripted tools/hooks — fully deterministic, no provider or key. It pins the paths you care about before you spend a token on a live run.

uv run mklang test examples/triage.mk --script examples/triage.test.yaml
# PASS happy-path
# PASS kb-empty-escalates

Each scenario declares a scripted llm:/tools:/hooks: and an expect: (status, error, result, at, trace skeleton, context keys) — the same case format the conformance suite uses. A mismatch prints a minimal diff (the first differing key, expected vs actual) and exits 1. See examples/triage.test.yaml.

Status

Language v0.2 / package 0.5.4 — core complete: states + gates + prose, tiers, reason / accumulate / fan-out / call / tool states / code-hook gates; multi-provider interpreter with entry-point plugins (tools, hooks, providers); resumable checkpoints (mklang resume, ADR 0007); human-in-the-loop (--hitl, ADR 0008); mklang check / lint / test (scripted scenarios, no API keys); implementation-neutral conformance suite (ADR 0009). Gate judging follows the state tier by default; see CHANGELOG 0.5.2 for the observable change and 0.5.3 for authoring tooling.

• Live: DeepSeek (default) and OpenAI green (2026-07-16), including examples on the current OpenAI tier map (fast: gpt-5.4-mini, balanced/reasoning: gpt-5.5 — latest chat-completions models on this account; gpt-5.5-pro is Responses-API only and not mapped). Anthropic unit-tested; live blocked by provider billing. Gate-divergence (deepseek×openai): agreement 1.0 — see docs/experiments/gate-divergence.md.
• Release policy: DeepSeek + OpenAI smoke and three-run gate agreement are blocking; other configured providers are reported without blocking. PyPI publication uses GitHub OIDC Trusted Publishing from the release workflow.
• Open: Anthropic live once the account has credit; accept/implement ADR 0011 (MCP) and then ADR 0010 (LLM lint) when ready.
• Roadmap and full release notes: ROADMAP.md, CHANGELOG.md.

License

Apache-2.0. Contributions welcome — see CONTRIBUTING.md.