mklang 0.10.0

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

See it in action

CLI: check, lint, and run	Console: self-consistency fan-out	Agent: free-language chained flows

HITL: suspend and resume	Search: live web tool	Tests: no API key

All recordings run the real surfaces against DeepSeek — the agent and search demos also hit the live web — except the test demo, which is fully deterministic and needs no API key. See the full WebM recordings, transcripts, and reproducibility notes.

The idea

Each state has four faces:

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

Sticky policy goes in execution; turn data and {{context}} go in prompt. There is no system: keyword — see Best practices §3.

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/ — guides/ (best practices, patterns, authoring, console, install), reference/ (CLI, stdlib, cheatsheet, architecture), demos.md, and the ADR index; plus ROADMAP.md.
• examples/ — runnable machines:
  • triage.mk — branching FSM + real search_kb / send_reply tools.
  • research.mk — looping FSM (iterative Q&A, training knowledge).
  • research_web.mk — research loop with tool: search (host-bound).
  • research_compress.mk — same + explicit notes compression.
  • news_search.mk — topic → tool: search → news brief (today + recency).
  • 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/guides/patterns.md.

Eight of these ship as ready, general-purpose std_* machines — parameterized by context, callable from your machines (call: std_refine), runnable by name:

mklang run std_self_consistency --set task="Estimate the risk of X"

See the stdlib catalog (ADR 0012). The patterns that need host tools/hooks or static call: targets (ReAct, router, exact policy) stay as authored examples.

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 parse: list (0.3) → 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

pipx install 'mklang[console,mcp]'   # or: pip install 'mklang[console,mcp]'
mklang init --user                   # scaffold config, .env, and a sample machine
# set DEEPSEEK_API_KEY (or another provider key) in the .env that init reported, then:
mklang console

The full walk-through — including a first run that needs no API key — is the Getting started guide. A one-shot scripts/install.sh and an Arch Linux PKGBUILD are also available.

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 (from a checkout)

Working on mklang itself, or preferring the repo? Clone it and drive everything through uv — no install step needed:

git clone https://github.com/gianlucamazza/mklang && cd mklang
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"

For an installed package outside this repository, follow the Getting started guide; host layout details are in the installation guide. Every command, flag, and exit code: CLI reference.

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.

MCP server (agentic hosts)

Agent hosts that speak MCP (Claude Code and other clients) can commission a machine instead of embedding the library (ADR 0011): the host requests a run and gets back the result with full provenance (trace + usage).

pip install 'mklang[mcp]'
claude mcp add mklang -- mklang-mcp --config /abs/path/to/runtime.yaml

The server exposes commissioning tools (run / resume), discovery (list_machines / describe_machine), and check (ADR 0011 + 0013). run accepts inline .mk source or a path, with inputs merged into the context; resume takes an opaque handle or checkpoint file (e.g. {"human.reply": "…"} for HITL). Live engine events stream as mklang.event logging notifications (ADR 0019). In-memory sessions hold suspensions unless you pass checkpoint_path. Provider keys resolve server-side from the environment, never over the wire.

Console (interactive)

mklang console (extra mklang[console]) is the agent-first front door: type what you want, the console's agent authors or picks a machine, commissions it, and streams the run state-by-state — escalations and tool consent come back to you inline. The agent itself is a machine (agent.mk) — read it, lint it, swap it with --agent your_brain.mk (ADR 0015). Agent replies render as Markdown; the brain declares host clocks today / now for wall-clock questions. Details: docs/guides/console.md.

pip install 'mklang[console]'
mklang console

Status

Language v0.3 / package 0.10.0 — core complete: states + gates + prose, tiers, reason / accumulate / fan-out / call / tool / parse: list / code-hook gates; multi-provider interpreter with entry-point plugins (tools, hooks, providers, machines); resumable checkpoints + HITL; mklang check / lint (--llm optional) / test; conformance suite; machine stdlib (std_*); MCP host; console TUI (M1–M3); structured web search (offline stub by default); host tool stub architecture for search / search_kb / send_reply (ADR 0020); host clock conventions context.today / context.now; sectioned produce system prompts from structure+execution; output anti-cutoff + context budgets (ADR 0016–0019); best practices. Gate judging follows the state tier by default.

• Live: DeepSeek (default) and OpenAI green in the latest (0.9.3) release matrix, including gate-divergence agreement 1.0 on the synthetic harness — see docs/experiments/gate-divergence.md. Anthropic unit-tested; live may be billing-blocked.
• 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 / later: Anthropic live when the account has credit; on_truncate=continue stitching; std_research / language-level context zones (ROADMAP).
• Roadmap and full release notes: ROADMAP.md, CHANGELOG.md.

License

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