SWMM Runner (CLI-first)

Part of Agentic SWMM — install the project first for the executable toolchain (aiswmm CLI, SWMM solver, MCP servers).

What this skill provides

• Deterministic execution wrapper around the swmm5 binary.
• A standard run directory layout: inp/, rpt/, out/, stdout, stderr, manifest.json.
• Metric extraction read directly from SWMM's own .rpt:
  • peak flow + time-of-peak for any junction or outfall;
  • Runoff Quantity and Flow Routing continuity tables + continuity error %;
  • cross-run comparison (e.g. GUI vs CLI) on continuity error.

When to use this skill

Use after a SWMM model is fully assembled (typically by swmm-builder.build_inp) and you need to actually execute it and read back the metrics. Also use to compare two .rpt files for regression / GUI parity.

Do not use this skill to assemble the .inp itself (that's swmm-builder) or to plot the results (that's swmm-plot).

MCP tools

mcp/swmm-runner/server.js exposes four tools.

1. swmm_run — run swmm5 against an .inp and write rpt + out + stdout + stderr + manifest.json into a run directory.

   • Args: inp (path), runDir (path), node (optional), rptName (optional), outName (optional).
   • When node is omitted, the server auto-detects the first entry from the .inp [OUTFALLS] section so the manifest's peak metric targets a real outfall name (no more silent "O1" default).
   • Output: a manifest with inp_sha256, swmm5 version, file paths, metrics.peak, metrics.continuity.

2. swmm_peak — parse peak flow and time-of-peak for a specific node from a SWMM .rpt. The node argument is required (no default; the previous misleading "O1" default has been removed).

   • Args: rpt (path), node (required).
   • Falls back from "Node Inflow Summary" to "Outfall Loading Summary" when no timed inflow entry exists for the node.

3. swmm_continuity — parse the Runoff Quantity and Flow Routing continuity tables from a SWMM .rpt.

   • Args: rpt (path).
   • Returns a structured dict with Continuity Error (%) for both blocks plus all the volume rows (precipitation, evaporation, infiltration, runoff, etc.).

4. swmm_compare — compare continuity-error percentages between two .rpt files (e.g. GUI vs CLI parity check).

   • Args: rpt, rpt2.

Recommended orchestration

swmm-builder.build_inp      → model.inp
swmm-runner.swmm_run        → model.rpt + manifest.json (with peak + continuity)
swmm-runner.swmm_continuity → structured continuity tables
swmm-runner.swmm_peak       → peak at a specific node (e.g. for downstream plotting)
   ↓
hand off to swmm-plot or swmm-experiment-audit

Conventions

• Read SWMM's own .rpt for continuity and peak metrics; do not re-implement physics.
• Keep units explicit in the .inp; SI preferred (FLOW_UNITS CMS).
• The .rpt's "Node Inflow Summary" is the authoritative peak source for both junctions and outfalls. If a node has only outfall flow (rare), the parser falls back to "Outfall Loading Summary".

Known limitations

• swmm_peak rounds to .rpt's 3-decimal display precision. Tiny basins (\x3C ~3 ha) routinely produce peaks of order 1e-4 m³/s that show up as 0.000 in the .rpt summary; the .out time-series file has the real precision but is not yet consulted (BACKLOG.md M3).
• swmm_continuity and swmm_peak return structured dicts but do not yet support an outputPath to write them as standalone JSON artifacts; the orchestrator currently captures them via the raw MCP response (BACKLOG.md F10).