sim-cli

sim-cli is a CLI-first runtime for Codex, Claude Code, and other AI coding agents to operate CAE solvers through plugins and skills.

sim is an open-source CLI and local runtime that lets Codex, Claude Code,
GitHub Copilot, Gemini, and other agents work with simulation software through
solver-specific plugins and bundled skills. An agent can check what is
installed, connect to a solver, inspect live state, execute bounded steps,
capture artifacts, and leave checkpoints for an engineer to review.

Quick Start · COMSOL + Codex · Agent Loop · Remote Solvers · Plugins · Commands

Who this is for

sim is for agents and people trying to get real simulation work done.

• CAE engineers who already script solvers and want an agent to help
  automate COMSOL, Fluent, MATLAB, LTspice, Abaqus, HFSS, and similar tools
  without losing inspection and recovery between steps.
• Design engineers and occasional simulation users who have agent
  experience and want an agent-assisted workflow: ask for a simulation, watch
  the model evolve, review screenshots or plots, and keep final artifacts.
• AI agents reading this repository to learn the safe setup and operating
  loop before touching a solver.
• Engineering leaders evaluating whether agent-assisted simulation can be
  repeatable, reviewable, and compatible with existing solver installations.

Plugin authoring, runtime internals, and driver protocol details live in
docs/DEVELOPMENT.md.

What sim gives an agent

LLMs can often write solver scripts, but a one-shot script is a weak workflow:
it hides intermediate state, fails late, and makes recovery difficult.

sim gives an agent a small, repeatable control surface:

check solver -> connect -> inspect -> execute one bounded step
-> inspect result/state -> save artifact or checkpoint -> continue

The solver-specific knowledge is not baked into the core CLI. It comes from
plugins. A plugin can provide both:

• a driver, so sim can launch or talk to the solver
• a skill, so the agent knows the solver-specific workflow, pitfalls, and
  inspection rules

Hosted engineering context is optional. When configured, agents can ask for a
Context7-style context pack before modeling:

$env:SIM_CONTEXT_API_KEY="sim_sk_..."
uv run sim context get --domain comsol "chip package overheating near voltage regulator"

The context API returns source pointers and engineering hints. It does not
replace local solver execution or expose private index internals.

Human-in-the-loop collaboration

sim is designed for shared control, not unattended black-box automation.
When a solver plugin exposes live state through sim inspect, the agent can
re-read the current solver session after each meaningful step. That means an
engineer can cut in through the solver GUI, change geometry, parameters,
boundary conditions, plots, or saved artifacts, then ask the agent to inspect
again and continue from the real current state.

This is the collaboration model: the human can watch, correct, and steer; the
agent keeps using inspection and checkpoints instead of assuming its previous
script still matches the real solver state.

Quick Start: agent setup

Use this path when the agent and solver are on the same machine. You do not
need to start sim serve manually for the local happy path; sim connect
will use the local runtime. The default docs use
uv so agents run the sim and plugins declared
by the current project instead of guessing which executable is on PATH.

uv run sim ... runs sim from this project environment, so it sees this
project's installed solver plugins. Run from the project root:

uv init  # only if this is not already a uv project
uv add sim-cli-core sim-plugin-comsol
uv run sim plugin sync-skills --target .agents/skills --copy
uv run sim check comsol
uv run sim plugin doctor comsol --deep

Use .agents/skills for Codex and GitHub Copilot projects. For Claude Code,
sync to .claude/skills instead:

uv run sim plugin sync-skills --target .claude/skills --copy

Without uv

If you cannot use uv, create a normal Python virtual environment, install
sim-cli-core and the solver plugin into that environment, then run sim
from the activated environment.

macOS/Linux:

python -m venv .venv
source .venv/bin/activate
python -m pip install --upgrade pip
python -m pip install sim-cli-core sim-plugin-comsol
sim plugin sync-skills --target .agents/skills --copy
sim check comsol
sim plugin doctor comsol --deep

Windows PowerShell:

py -m venv .venv
.\.venv\Scripts\Activate.ps1
python -m pip install --upgrade pip
python -m pip install sim-cli-core sim-plugin-comsol
sim plugin sync-skills --target .agents/skills --copy
sim check comsol
sim plugin doctor comsol --deep

Hand this prompt to your agent

After setup, give your coding agent a direct instruction like this:

Use the installed solver skill. Run sim through this project with
`uv run sim ...`. Check my local solver installation before connecting. Work
one bounded step at a time: connect, inspect the session, execute a small step,
inspect last.result and the live model state, then save or update a checkpoint
before continuing. Do not guess solver API names; inspect the live model or the
solver's local docs first. If I make manual changes in the solver UI,
re-inspect the live state before continuing instead of assuming your previous
script still matches the model. Report saved artifacts, numerical checks,
warnings, and anything that still needs human engineering review.

Example: COMSOL and Codex on one machine

If COMSOL and Codex are on the same machine, start by installing the COMSOL
plugin and syncing its bundled skill into the .agents/skills project target:

uv add sim-cli-core sim-plugin-comsol
uv run sim plugin sync-skills --target .agents/skills --copy
uv run sim check comsol
uv run sim plugin doctor comsol --deep

Then ask Codex:

Use the installed COMSOL skill. Start by checking COMSOL through `uv run sim
check comsol`. If you need a visible live COMSOL Desktop session, use:

uv run sim connect --solver comsol --ui-mode gui --driver-option visual_mode=shared-desktop

After connecting, inspect session.health and comsol.model.identity. Confirm the
live model binding is healthy before treating the GUI as synchronized. For
non-trivial work, establish a case folder and save .mph checkpoints after major
layers. Build and solve one bounded step at a time.

For COMSOL-specific details such as shared Desktop mode, offline .mph
inspection, Desktop attach fallback, model identity checks, and checkpoint
policy, follow the bundled COMSOL skill.

Why CLI-first?

sim-cli is CLI-first because engineering simulation is file-based,
scriptable, local, artifact-heavy, and long-running.

CAE agents need to work with solver executables, model files,
Python/Java/journal scripts, shell commands, logs, checkpoints, plots,
and artifacts. A CLI command surface composes with all of that and
matches how Codex CLI, Claude Code, and other coding agents already
operate.

MCP is useful for API-style integrations and remote tool discovery,
but a broad MCP surface can add context overhead and wrapper
maintenance. For COMSOL, Abaqus, Ansys Workbench, OpenFOAM, LTspice,
and similar solvers, sim-cli keeps the source of truth as a small,
auditable command loop:

check → connect → inspect → execute one bounded step → verify → save artifacts

Solver plugins provide solver-specific behavior. Agent skills teach
Codex, Claude Code, and other agents when and how to use the CLI
safely.

The agent loop

For any solver, the agent should prefer this loop over one large generated
script:

1. uv run sim check <solver> to detect installed solver versions and plugin
   compatibility.
2. uv run sim connect --solver <solver> ... for live stateful work, or
   uv run sim run for a deterministic one-shot script.
3. uv run sim inspect session.versions and the solver-specific health or
   identity target before changing state.
4. uv run sim exec --file step.py --label <step> for one bounded modeling
   or analysis step.
5. uv run sim inspect last.result and solver-specific state before
   continuing.
6. Save checkpoints and artifacts when the solver plugin or skill requires
   them.
7. uv run sim disconnect when the session is done.

Screenshots and plots help humans review the result, but engineering
acceptance should prefer numeric evidence when the solver skill defines it:
mesh statistics, convergence, finite probes, conservation checks, tolerances,
or expected trends.

Local vs remote solvers

Same machine: install sim-cli-core and the solver plugin into the project
environment, sync the skill to your agent, then use uv run sim connect. Do
not add --host unless you are intentionally talking to a remote sim serve.

Remote solver workstation, lab box, or HPC login node: install
sim-cli-core and the solver plugin on the solver host, start sim serve
there, then point the local agent at that host:

# On the solver host.
uv run sim serve --host 0.0.0.0 --port 7600

# On the agent/control machine.
uv run sim --host <solver-host-ip> check <solver>
uv run sim --host <solver-host-ip> connect --solver <solver>
uv run sim --host <solver-host-ip> inspect session.summary
uv run sim --host <solver-host-ip> disconnect

Only bind sim serve to a trusted network such as a VPN, Tailscale, or a
protected LAN. The runtime currently has no auth layer, and /connect plus
/exec can execute solver-side code.

Solver plugins

sim-cli-core ships with no solver drivers built in. Each simulation solver is
reached through an explicit plugin package.

Ready-to-use plugins:

Under development: Amesim, Dymola, and Flotherm.

After adding any plugin package, sync its bundled skill and verify that the local
solver can be reached:

uv run sim plugin list

# Codex or Copilot
uv run sim plugin sync-skills --target .agents/skills --copy

# Claude Code
uv run sim plugin sync-skills --target .claude/skills --copy

uv run sim check <solver>
uv run sim plugin doctor <solver> --deep

For direct wheel, Git, local checkout, or non-uv workflows, see
docs/plugin-install.md.

Project setup with sim.toml

For reproducible Python packages, commit the pyproject.toml and uv.lock
created by uv add. Use sim.toml for solver defaults and workspace settings:

uv run sim init

Example:

[sim]
default_solver = "comsol"
workspace = "./workspace"

[[sim.plugins]]
name = "comsol"
package = "sim-plugin-comsol"

Then a fresh checkout can run:

uv sync
uv run sim setup --dry-run

# Codex or Copilot
uv run sim plugin sync-skills --target .agents/skills --copy

# Claude Code
uv run sim plugin sync-skills --target .claude/skills --copy

Common commands

Run uv run sim describe for a machine-readable command manifest, or
uv run sim <command> --help for exact options.

Solver ownership

sim-cli does not bundle or redistribute simulation solvers or vendor SDKs.
Install and operate each underlying solver according to its vendor terms. See
NOTICE for optional SDK dependency notes.

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 remain the property of their respective owners.

Developer docs

• docs/DEVELOPMENT.md - project setup, layout, driver
  development, and architecture notes
• docs/plugin-install.md - plugin installation
  reference

License

Apache-2.0 - see LICENSE.