Create a new Stella model with specified time settings

Create and populate a model in one call: sim specs, stocks, auxiliaries, flows, connectors, and modules. All-or-nothing — on any item error nothing is registered and the error names the failing item (stage + index). Connector sync and validation run by default, so the response doubles as an inspection.

Add multiple stocks, auxiliaries, flows, connectors, and/or modules to an existing model in one call. All-or-nothing — on any item error the model is left unchanged and the error names the failing item (stage + index).

Update simulation time settings on an existing model

Add a stock (reservoir) to the current model

Update stock fields while preserving relationships

Add a flow between stocks in the current model

Update flow fields while preserving structural stock links

Add an auxiliary variable (parameter or intermediate calculation) to the current model

Update auxiliary variable fields

Add a connector (dependency arrow) between variables

Add missing dependency connectors inferred from flow and auxiliary equations

Set connector angle and/or explicit routing waypoints

Rename a stock/flow/aux and update dependent references

Delete a stock/flow/aux and clean connectors/module membership

Create a logical module/group for organizing variables

Add variables to an existing module

Remove variables from an existing module

Rename an existing module

Delete a module

Set explicit view box geometry for a module

Set module box visual style in the diagram view

Auto-place module view boxes around their member variables

Save the current model to a .stmx file

Render the current model as an SVG stock-and-flow diagram. The SVG is returned inline (for clients without file access) and optionally written to a file. Defaults to running auto-layout first so freshly built models render sensibly.

Read an existing .stmx file and load it as the current model

List built-in and user-defined templates

Get detailed metadata for one template

Load a template into the current session as a model

Save the current model as a user-defined template

Run the model and return downsampled time series with per-variable summaries (initial/final/min/max). Requires the optional pysd dependency (pip install 'stella-mcp[sim]'). Integration is Euler regardless of the model's method setting.

Run several named what-if scenarios (each a set of constant parameter overrides) against a baseline and report how each diverges: per-variable final/max absolute deltas and final percent change. Requires the optional pysd dependency (pip install 'stella-mcp[sim]').

One-at-a-time sensitivity: sweep each parameter across a range (holding the others at their baseline) and report how one chosen output metric responds, with a range slope and a baseline-normalized elasticity for ranking. Requires the optional pysd dependency (pip install 'stella-mcp[sim]').

Fit constant model parameters to an observed time-series — the inverse of simulate. Only constant auxiliaries/flows can be calibrated (stocks are rejected: overriding a stock pins it to a constant rather than setting its initial value). least_squares (default) reports a linearized std_error; differential_evolution is a global, seeded alternative requiring bounds. Observation times must lie within the model window (no extrapolation). Requires the optional pysd dependency (pip install 'stella-mcp[sim]').

List all model IDs available in the current session

Remove a model from the current session. Saved .stmx files are not touched. model_id is required — there is deliberately no implicit 'delete current model'.

Return a structured summary of the current model for agent inspection

List modules/groups in the current model

List connector metadata (uid, endpoints, angle, routing lock/points)

Validate the current model for errors and warnings

List all variables (stocks, flows, auxiliaries) in the current model

Get the XMILE XML representation of the current model (for preview)

Create an isolated application workspace for stateful Stella tool calls. The returned ID routes state and is not an authorization credential.

Revoke a workspace and discard all models stored in it.