casino-mcp

An MCP control plane over the Fortran CASINO quantum Monte Carlo code: start runs, know what is running, stop them, and read an out file as structured data instead of shipping 4000 lines of text into a model's context.

Beta (0.2.0). The four control tools and the out parser are done and tested against a real CASINO; the tool that returns physics to the model is not shipped yet. Interfaces may still move before 1.0.

What it is, and what it is not

CASINO already has the primitives — opt_plan, runqmc --auto-continue, multirun, envmc, make_E_v_dt. What it has no place for is the layer between them: machine-readable results, a memory of what was run, and the judgement calls that sit between the steps ("has the variance plateaued?", "is this timestep still in the linear regime?"). That layer is what this package is, and three rules keep it honest:

1. No number is produced by the model. Every value a tool returns is read from a file and carries the line it came from. What CASINO did not print comes back as null with a reason, never a guess.
2. Every result is reproducible from its record. A job record freezes the command, the process count, and the path, size and mtime of the casino binary that ran.
3. Nothing destructive is implicit. A run refuses to start in a directory that already holds results, and refuses harder when that out is committed reference data.

There is deliberately no execute_shell(command) tool. Every tool is a named CASINO operation with typed arguments.

Install

pip install casino-mcp          # needs Python 3.11+ and a working CASINO installation

From a checkout:

pip install -e '.[dev]'

The package does not bundle, build or replace CASINO. It drives runqmc, which stays the runtime: arch detection, MPI variants, batch-queue submission and the lock file are its job, not ours.

Register it with Claude Code

.mcp.json, project scope:

{
  "mcpServers": {
    "casino": {
      "command": "casino-mcp",
      "args": ["serve"],
      "env": {
        "CASINO_HOME": "/home/you/bin/CASINO",
        "CASINO_ARCH": "linuxpc-gcc-parallel.openblas"
      }
    }
  }
}

Tools

tool	returns
casino_run(workdir, nproc, version, restart, resume, unlock)	job_id, pid, workdir, command, binary stamp, what restart removed
casino_status(job_id)	running / finished / failed / stopped / unknown, pid, runtime, exit code
casino_stop(job_id, timeout)	what was signalled, final status, what haltqmc did
casino_list_jobs(limit)	every known job, newest first

The runtype (vmc, vmc_opt, vmc_dmc, …) comes from the input file in workdir; there is no tool per runtype, because that multiplies the surface without adding a capability.

Starting, stopping and continuing a calculation all go through CASINO's own scripts, and only through them: runqmc starts, haltqmc ends and tidies, runqmc --continue or a plain runqmc over the input that haltqmc -u rewrote carries on. Nothing here moves a config file, edits an input, or decides what a half-finished calculation should do next.

A directory that already holds an out

runqmc appends to out, vmc.hist and dmc.hist rather than replacing them, so running twice in one directory produces files that are two runs glued together. That is refused by default, and there are two ways past it — opposites, so pass one:

restart=true	delete what the earlier run left and start over. out, out_part.N, the .hist files, config.in/config.out, correlation.out.N, parameters.N.casl, saved_part_N/. The inputs stay: input, the wave function, the pseudopotentials, correlation.data, parameters.casl. Every deleted name comes back in the reply, under removed.
resume=true	carry the interrupted run on from where it stopped. Which of CASINO's two continuation routes that takes is read out of out, not chosen here — see below.

On the command line these are --restart and --resume, and --continue is accepted for the latter, which is what runqmc calls it. The tool parameter cannot be spelled that way: continue is a Python keyword.

Stopping a run, and continuing it

casino_stop sends SIGTERM to that job's casino processes and to nothing else — the same signal haltqmc -k sends, except that haltqmc's is a pkill -x casino over the whole account, which would take down every other job on the machine. mpirun puts each rank in a process group of its own, so the ranks are found by session id: the session is the launcher's, and the whole tree shares it. runqmc itself is left alive to finish its epilogue, and only a job still running after timeout has its process group signalled and then killed.

Then the directory goes to haltqmc -f -u, which is the part that makes a stopped run continuable: config.out becomes config.in, the lock and marker files go, and input is rewritten for the work that is left — newrun : F, the finished blocks subtracted, the runtype moved on to the next stage. The reply carries what it did under halt. The input as it was before that is copied into the job directory, and halt.input_saved says where.

Which continuation route resume=true then takes is decided by the last run in out:

CONTINUATION INFO: in out	runqmc --continue. CASINO writes that block only when it stops itself on max_cpu_time or max_real_time; runqmc applies it and archives the finished segment into saved_part_N/.
no such block	a plain runqmc over the input haltqmc rewrote. This is how an interrupted run continues — --continue would only errstop on the missing continuation info.
the run reached its own end	refused: there is nothing to continue.

restart=true is refused on a directory whose input says newrun : F, because restarting deletes the config.in that CASINO then demands. Put back the saved input first.

Command line

The same runtime without a model in the loop — which is also how you debug the server:

casino-mcp config                  # the resolved configuration, and the files it came from
casino-mcp run ./calc -p 4         # start a calculation
casino-mcp run ./calc --restart    # ... after deleting what an earlier run left there
casino-mcp run ./calc --continue   # ... or carrying that run on instead
casino-mcp status 20260823-164511-qobn
casino-mcp stop   20260823-164511-qobn   # stop the run, then hand the directory to haltqmc
casino-mcp jobs                    # the registry, newest first
casino-mcp parse ./calc            # the `out` file as JSON
casino-mcp serve                   # the MCP server on stdio

Every subcommand prints JSON and exits non-zero when that JSON carries an error.

Configuration

There is no configuration file. An MCP server is configured where it is registered — the env block of the .mcp.json above — and CASINO's own variables keep their names, so setting them once configures both layers:

variable
CASINO_HOME	root of the CASINO installation (default ~/bin/CASINO)
CASINO_ARCH	build target, the directory under bin_qmc; used to stamp which binary a job ran
CASINO_RUNQMC	explicit path to runqmc; otherwise PATH, then $CASINO_HOME/bin_qmc/runqmc
CASINO_HALTQMC	explicit path to haltqmc; otherwise PATH, then $CASINO_HOME/bin_qmc/haltqmc
CASINO_MCP_STATE_DIR	the job registry; otherwise $XDG_STATE_HOME/casino-mcp
CASINO_MCP_FORBID	directories no run may ever touch, :-separated like PATH

Everything else — one MPI process, the opt binary, twenty seconds for a stopped job to end on its own, a minute for haltqmc to tidy, two hundred job records kept — is a constant in settings.py. casino-mcp config prints what the server would use right now and which variable said so; run it first when a tool call refuses.

CASINO_MCP_FORBID is the one guard with no per-call override. restart=true/resume=true and unlock=true unlock the other two; a directory listed here cannot be run in at all, which is what makes it the right place for a tree of committed reference calculations.

How it works

Claude Code ──stdio──> server.py ──spawn──> launcher.py ──> runqmc ──> mpirun ──> casino
                          │                     │
                          │                     └─ writes status.json (exit code, end time)
                          └─ reads/writes jobs.json + one directory per job

State lives outside the calculation, under $XDG_STATE_HOME/casino-mcp/:

jobs.json                    index: job_id -> record
jobs/<job_id>/meta.json      what was launched, frozen at spawn
jobs/<job_id>/status.json    written by the launcher when the run ends
jobs/<job_id>/runqmc.log     runqmc's own output (not CASINO's `out`)
jobs/<job_id>/input.before_halt   the input as it was, kept when a stop rewrites it

The calculation directory only ever gets what CASINO puts there.

Why a launcher process. runqmc is a bash script that execs mpirun -np N casino; signalling its pid orphans the tree. The launcher runs in its own session, which is what makes the tree identifiable — killpg reaches runqmc and mpirun, and the session id finds the ranks that mpirun put in process groups of their own — its exit code survives the MCP server being restarted, and runqmc's output goes to a log instead of the JSON-RPC stream. A recycled pid cannot pass for a live job: /proc/<pid> start time is compared, and a zombie does not count as running.

The out parser

parse_out is a plain function with no MCP and no dependencies. An out file is a sequence of phases, not one result — vmc_opt writes a VMC and an OPTIMIZATION phase per cycle, vmc_dmc writes VMC, DMC equilibration and DMC statistics accumulation — so it returns phases, and result points at the last phase that carries an energy.

from casino_mcp.parse_out import parse_out

parsed = parse_out('./calc')
parsed['result']['energy']  # {'value': -2.861829862553, 'error': 0.000659077167, 'line': 237}

The one derived number in it is the sample-variance error of a single-block run, which CASINO does not print; it is taken from the one block exactly as envmc does, and labelled derived. Nothing shells out to envmc or endmc at runtime — endmc misparses numbers under a non-C locale.

Tests

pytest                      # 158 tests, ~5 s, no CASINO needed

The unit suite runs anywhere: the parser is checked field by field against five real out files under tests/data/ — each with the input that produced it — and over all eighteen calculations under examples/, while the launcher, the process group and the guardrails are exercised against a fake runqmc shell script.

pytest -m integration

The integration suite needs a real CASINO, but nothing outside this repository. It checks parse_out against CASINO's own envmc over every out in examples/, re-runs the whole tree against the installed binary, and drives the server over real stdio MCP, running and stopping actual VMC calculations.

examples/ holds eighteen calculations chosen as a cover of the settings CASINO can be run with — every runtype, basis type, optimiser and wavefunction option appears at least once, and so do the two files a parser gets wrong quietly: a run that never printed an energy, and one interrupted between optimisation cycles. examples/README.md says what each is there for.

They are short and seeded, so the tree doubles as a check on CASINO itself: re-run it on a new release and any line the parser reads that has been renamed or dropped is named, rather than silently becoming a None. Only that is asserted — moved numbers are reported for a person to judge.

python tools/refresh_examples.py --nproc 4     # run the tree, report, touch nothing
python tools/refresh_examples.py --nproc 4 --write   # adopt the new output

tools/protocol_dump.py speaks the JSON-RPC by hand with no SDK and prints every line in both directions. Read it before adding a tool.

Licence

MIT.