sim-cli-core 0.3.0

Make every engineering tool agent-native — a CLI runtime that lets LLM agents launch, drive, and observe CAD/CAE software

Make every engineering tool agent-native.

Today's CAD and CAE software was built for engineers clicking through GUIs. Tomorrow's user is an LLM agent — and it needs a way in.

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Why sim · Quick Start · Solvers · Commands · Demo · Skills

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🤔 Why sim?

LLM agents already know how to write simulation scripts — training data is full of them. What they don't have is a standard way to launch a solver, drive it step by step, and observe what happened before deciding the next move.

Today, the choices are awful:

• Fire-and-forget scripts — agent writes 200 lines, runs the whole thing, an error at line 30 surfaces as garbage at line 200, no introspection, no recovery.
• Bespoke wrappers per solver — every team rebuilds the same launch / exec / inspect / teardown loop in a different shape.
• Closed proprietary glue — vendor SDKs that don't compose, don't share a vocabulary, and don't speak HTTP.

sim is the missing layer:

• One CLI, one HTTP protocol, a growing driver registry spanning CFD, multiphysics, thermal, pre-processing, and beyond.
• Persistent sessions the agent introspects between every step.
• Remote-by-default — the CLI client and the live solver can sit on different machines (LAN, Tailscale, HPC head node).
• Companion agent skills that teach an LLM how to drive each backend safely.

Like a container runtime standardized how Kubernetes talks to containers, sim standardizes how agents talk to solvers.

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🏛 Architecture

Two execution modes from the same CLI, sharing the same DriverProtocol:

Mode	Command	When to use it
Persistent session	sim serve + sim connect / exec / inspect	Long, stateful workflows the agent inspects between steps
One-shot	sim run script.py --solver X	Whole-script jobs you want stored as a numbered run in .sim/runs/

For the full driver protocol, server endpoints, and execution pipeline see CLAUDE.md.

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🚀 Quick Start

Names at a glance: repo svd-ai-lab/sim-cli · PyPI distribution sim-cli-core · console command sim · import import sim. Yes, three different strings — the repo name predates the PyPI publish; the rest follow Python packaging convention.

# 1. On the host that has the solver installed, install sim core only
#    — no driver choice yet:
uv pip install sim-cli-core

# 2. Install the plugin for the solver you actually want (browse the
#    index with `sim plugin list`):
sim plugin install <solver>     # e.g. ltspice, coolprop, pybamm

# 3. Tell sim to look at this machine and pick the right SDK profile:
sim check <solver>
# → reports detected installs of <solver> and the profile they resolve to

# 4. Bootstrap that profile env (creates .sim/envs/<profile>/ with the
#    pinned SDK; or pass --auto-install to step 5 to do it inline):
sim env install <profile>

# 5. Start the server (only needed for remote / cross-machine workflows):
sim serve --host 0.0.0.0          # FastAPI on :7600

# 6. From the agent / your laptop / anywhere on the network:
sim --host <server-ip> connect --solver <solver> --mode solver --ui-mode gui
sim --host <server-ip> inspect session.versions   # ← always do this first
sim --host <server-ip> exec "<solver-specific snippet>"
sim --host <server-ip> screenshot -o shot.png
sim --host <server-ip> disconnect

That's the full loop: detect → bootstrap → launch → drive → observe → tear down — with the engineer optionally watching the solver GUI in real time.

Why the bootstrap step? Each (solver, SDK, driver, skill) combo is its own compatibility universe — different solver releases may want different SDK versions, and those SDK versions can't always coexist in one Python env. sim treats each combo as an isolated "profile env" so you can keep multiple versions on one machine without dependency conflicts. The contract is in docs/architecture/version-compat.md.

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🧪 Solver registry

sim-cli core is fully solver-agnostic — it ships with zero built-in drivers. Every solver, including OpenFOAM, is reached through an out-of-tree plugin package registered via the sim.drivers entry-point group. Adding a new backend is a ~200-LOC DriverProtocol implementation in its own sim-plugin-<name> repo.

Plugin coverage spans CFD, multiphysics, electronics thermal, implicit and explicit structural FEA, pre/post-processing, mesh generation, embodied-AI / GPU physics, molecular dynamics, optimization / MDAO, battery modeling, thermo properties, power-systems and RF simulation, and discrete-event modeling. Browse the curated index:

sim plugin list                  # what the curated index advertises
sim plugin install <name>        # e.g. sim plugin install ltspice

The index is served from sim-plugin-index; reference plugins to read for shape: sim-plugin-coolprop (one-shot, no SDK gate), sim-plugin-ltspice (one-shot with vendor binary), sim-plugin-pybamm (heavy SDK).

Private plugins (vendor-IP-sensitive backends not in the public index) install directly by URL — same sim plugin install flow:

sim plugin install git+https://github.com/<org>/sim-plugin-<name>
# (you need read-access to the repo; without it, git clone returns 401)

Per-solver protocols, snippets, and demo workflows live in sim-skills and the per-plugin repos.

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🎬 Demo

📺 Early preview: first walkthrough on YouTube — rough cut, a polished recording is still wanted (see below).

Recording in progress. A short terminal capture of sim connect → exec → inspect → screenshot against a live solver session will land here.

Want to contribute the recording? Use vhs or asciinema and open a PR against assets/demo.gif.

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✨ Features

🧠 Built for agents

• Persistent sessions that survive across snippets — never restart the solver mid-task
• Step-by-step introspection with sim inspect between every action
• Pre-flight sim lint catches missing imports and unsupported APIs before launch
• Numbered run history in .sim/runs/ for one-shot jobs, browsable via sim logs

🔌 Solver-agnostic

• One protocol (DriverProtocol) — every driver is ~200 LOC, shipped as its own sim-plugin-<name> package via Python entry points
• Persistent + one-shot from the same CLI — no separate client per mode
• Open plugin index — discoverable via sim plugin list; curated registry at sim-plugin-index
• Companion skills in sim-skills so an LLM picks up each new backend without prior context

🌐 Remote-friendly

• HTTP/JSON transport — runs anywhere httpx runs
• Client / server split — agent on a laptop, solver on an HPC node, GUI on a workstation
• Tailscale-ready — designed for cross-network mesh deployments

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⚙️ Commands

Command	What it does	Analogy
sim plugin list / install / uninstall	Manage out-of-tree solver plugins from the curated index	npm install
sim check <solver>	Detect installations + resolve a profile	docker info
sim env install <profile>	Bootstrap a profile env (venv + pinned SDK)	pyenv install
sim env list [--catalogue]	Show bootstrapped envs (and the full catalogue)	pyenv versions
sim env remove <profile>	Tear down a profile env	pyenv uninstall
sim serve	Start the HTTP server (for cross-machine use)	ollama serve
sim connect	Launch a solver, open a session	docker start
sim exec	Run a Python snippet inside the live session	docker exec
sim inspect	Query live session state (incl. session.versions)	docker inspect
sim ps	Show the active session and its profile	docker ps
sim screenshot	Grab a PNG of the solver GUI	—
sim disconnect	Tear down the session	docker stop
sim stop	Stop the sim-server process	docker rm -f
sim run	One-shot script execution	docker run
sim lint	Pre-flight static check on a script	ruff check
sim logs	Browse stored run history	docker logs

Every command that touches a host (check, env, connect, exec, inspect, disconnect) accepts --host <ip> and runs against a remote sim serve instead of the local machine.

Environment: SIM_HOST, SIM_PORT for the client; SIM_DIR (default .sim/) for run storage and profile envs.

Choosing a profile

You don't usually have to. sim check <solver> tells you which profile your installed solver maps to, and sim connect ... --auto-install will bootstrap it for you on first use. The escape hatches:

• Pin a specific profile: sim connect --solver <solver> --profile <profile>
• Skip the profile env entirely (legacy / tests): sim connect --solver <solver> --inline
• Power-user single-env install: install the matching plugin package directly into your current venv (e.g. pip install <plugin-package>). Skips sim env entirely; OK when you only need one solver version on this machine.

The full design is in docs/architecture/version-compat.md.

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🆚 Why not just run scripts?

Fire-and-forget script	sim
Write the whole thing, run, hope it converges	Connect → execute → observe → decide next step
An error at step 2 surfaces at step 12	Each step verified before the next is sent
Agent has no view of solver state	sim inspect between every action
Solver restarts on every iteration	One persistent session, snippets at will
GUI invisible to the human	Engineer watches the GUI while the agent drives
Output parsing reinvented per project	driver.parse_output() returns structured fields

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🛠 Development

See docs/DEVELOPMENT.md for setup, project layout, adding drivers, dev flags, and the layered skill system.

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🌐 Remote deployment

When the solver lives on a different machine (an HPC login node, a lab box, or any host with the solver installed) and you want to drive it from your laptop, a notebook, or an LLM agent — install sim-cli-core on both ends and run sim serve on the remote.

# On the solver host (the machine with the solver installed)
ssh user@solver-host
pip install sim-cli-core
sim serve --host 0.0.0.0 --port 7600     # bind to all interfaces

# On your local control machine
sim --host <solver-host-ip> connect --solver <solver> --mode <mode>
sim --host <solver-host-ip> exec "<solver-specific snippet>"
sim --host <solver-host-ip> inspect session.summary
sim --host <solver-host-ip> disconnect
sim --host <solver-host-ip> stop          # shut down the remote server when done

That is the entire setup — same sim-cli-core package on both sides, same wire protocol whether it is talking to a local or a remote server. Bind --host 0.0.0.0 only on networks you trust (Tailscale, VPN, LAN behind a firewall); there is no auth layer on /connect and /exec execute arbitrary Python.

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🔗 Related projects

• sim-plugin-index — curated registry of out-of-tree solver plugins; what sim plugin list / install reads
• sim-skills — agent skills, snippets, and demo workflows for each supported solver
• sim-ltspice — standalone Python API for LTspice file formats (used by sim-plugin-ltspice)

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📄 License

Apache-2.0 — see LICENSE.

Third-party solver SDKs

sim-cli is a thin wrapper/runtime — it does not bundle or redistribute any vendor solver or vendor SDK. Each solver backend is reached through a third-party SDK that the user installs separately via sim env install or as an optional extra.

Users are responsible for obtaining a valid license for each underlying solver and for complying with the license, copyright, and EULA of every third-party SDK they choose to install alongside sim-cli. See NOTICE for the list of optional SDK dependencies and their upstream locations.

Trademarks

sim-cli is an independent open-source project and is not affiliated with, endorsed by, or sponsored by any solver vendor. Product, solver, and company names referenced anywhere in this repository remain the property of their respective owners:

• OpenFOAM® is a registered trademark of OpenCFD Ltd.
• ParaView® is a trademark of Kitware, Inc.
• All other solver and product names are trademarks of their respective owners.