Schematic and Netlist Tools

Eight tools for working with LTspice .asc schematics, SPICE .cir netlists, and Touchstone S-parameter files. These cover the full lifecycle: read an existing circuit, edit component values, compare revisions, run design rule checks, build new circuits from scratch or from templates, and parse RF measurement data.

---

read_schematic

Read and parse an LTspice .asc schematic file. Extracts all component instances with their symbols, values, positions, and attributes; net flag names; SPICE directives (simulation commands, .param, .lib, etc.); and wire count.

Parameter	Type	Default	Description
schematic_path	str	---	Path to the .asc schematic file.

Returns: A dict with version (schematic format version), components (array of objects each containing name, symbol, value, x, y, and attributes), nets (array of net flag names), directives (array of SPICE directive strings), and wire_count.

Example

{
  "version": 4,
  "components": [
    {
      "name": "R1",
      "symbol": "res",
      "value": "10k",
      "x": 192,
      "y": 128,
      "attributes": {"Value": "10k"}
    },
    {
      "name": "C1",
      "symbol": "cap",
      "value": "100n",
      "x": 320,
      "y": 128,
      "attributes": {"Value": "100n"}
    },
    {
      "name": "V1",
      "symbol": "voltage",
      "value": "AC 1",
      "x": 64,
      "y": 128,
      "attributes": {"Value": "AC 1"}
    }
  ],
  "nets": ["0", "in", "out"],
  "directives": [".ac dec 100 1 1meg"],
  "wire_count": 8
}

---

edit_component

Modify a component’s value in a schematic. Parses the .asc file, finds the component by instance name (case-insensitive), updates its value, and writes the result. Can overwrite the original file or save to a new path.

Parameter	Type	Default	Description
schematic_path	str	---	Path to the .asc schematic file.
component_name	str	---	Instance name of the component to modify, e.g. "R1", "C2", "M1".
new_value	str	---	New value string, e.g. "10k", "100n", "2N7000".
output_path	str | None	None	Where to save the modified schematic. None overwrites the original.

Returns: A dict with success (boolean), component (the component name), new_value, output_path (path written to), and symbol (the component’s symbol type). On failure, returns success: false with an error message listing available component names.

Example

{
  "success": true,
  "component": "R1",
  "new_value": "22k",
  "output_path": "/tmp/filter_modified.asc",
  "symbol": "res"
}

---

diff_schematics

Compare two schematics and produce a structured diff. Reports component additions, removals, and value changes; directive additions, removals, and modifications; net flag additions and removals; and wire count changes. Components are matched by instance name, so renaming a component shows up as a removal plus an addition.

Parameter	Type	Default	Description
schematic_a	str	---	Path to the “before” .asc file.
schematic_b	str	---	Path to the “after” .asc file.

Returns: A dict with has_changes (boolean), component_changes (array of objects with name, change_type of "added" / "removed" / "modified", symbol, old_value, new_value, old_attributes, new_attributes, and moved), directive_changes (array with change_type, old_text, new_text), nets_added, nets_removed, wires_added, wires_removed, and a human-readable summary string.

Example

{
  "has_changes": true,
  "component_changes": [
    {
      "name": "R1",
      "change_type": "modified",
      "symbol": "res",
      "old_value": "10k",
      "new_value": "22k",
      "old_attributes": {"Value": "10k"},
      "new_attributes": {"Value": "22k"},
      "moved": false
    },
    {
      "name": "C3",
      "change_type": "added",
      "symbol": "cap",
      "old_value": null,
      "new_value": "47n",
      "old_attributes": {},
      "new_attributes": {"Value": "47n"},
      "moved": false
    }
  ],
  "directive_changes": [
    {
      "change_type": "modified",
      "old_text": ".tran 1m",
      "new_text": ".tran 10m"
    }
  ],
  "nets_added": ["feedback"],
  "nets_removed": [],
  "wires_added": 3,
  "wires_removed": 0,
  "summary": "1 component modified:\n  R1: 10k -> 22k\n1 component added: C3 (cap) = 47n\n1 directive changed: .tran 1m -> .tran 10m\n1 net added: feedback\n3 wires added"
}

---

run_drc

Run design rule checks on a schematic. Parses the .asc file and runs seven checks against common issues that cause simulation failures or unexpected behavior. Each violation is classified as error (will likely prevent simulation), warning (may produce unexpected results), or info (suggestion).

Checks performed:

1. NO_GROUND — Missing ground (node 0) connection.
2. FLOATING_NODE — Wire endpoint with only one connection and no flag or component nearby.
3. NO_SIM_DIRECTIVE — No simulation command (.tran, .ac, .dc, .op, .noise, .tf).
4. VSOURCE_LOOP — Two voltage sources connected in parallel (short circuit).
5. MISSING_VALUE — Resistor, capacitor, inductor, or source with no value set.
6. DUPLICATE_NAME — Two components sharing the same instance name.
7. UNCONNECTED_COMPONENT — Component with no wire endpoints within one grid step of its origin.

Parameter	Type	Default	Description
schematic_path	str	---	Path to the .asc schematic file.

Returns: A dict with passed (boolean --- true if zero errors), checks_run (number of checks executed), summary (human-readable string), error_count, warning_count, and violations (array of objects each containing rule, severity, message, component, and location).

Example

{
  "passed": false,
  "checks_run": 7,
  "summary": "DRC FAILED: 7 checks run, 1 error, 1 warning.",
  "error_count": 1,
  "warning_count": 1,
  "violations": [
    {
      "rule": "NO_GROUND",
      "severity": "error",
      "message": "No ground node found. Every circuit needs at least one ground (0) connection.",
      "component": null,
      "location": null
    },
    {
      "rule": "MISSING_VALUE",
      "severity": "warning",
      "message": "Resistor 'R3' has no value set.",
      "component": "R3",
      "location": [320, 256]
    }
  ]
}

---

create_netlist

Create a SPICE netlist programmatically and save it as a .cir file. Build circuits from scratch without needing the LTspice graphical editor. The resulting file can be passed directly to simulate_netlist.

Parameter	Type	Default	Description
title	str	---	Circuit title/description (appears as the first line of the .cir file).
components	list[dict]	---	List of component dicts. Each must have name (e.g. "R1", "V1", "X1"), nodes (list of node name strings, use "0" for ground), and value (value or model name). Optional params key for extra parameters.
directives	list[str]	---	List of SPICE directive strings, e.g. [".tran 10m", ".meas tran vmax MAX V(out)"].
output_path	str | None	None	Where to save the .cir file. None saves to a temp directory with a name derived from the title.

Returns: A dict with success (boolean), output_path (where the file was written), netlist_preview (full rendered netlist text), and component_count.

Example — RC lowpass filter

Calling create_netlist with these arguments:

{
  "title": "RC Lowpass Filter",
  "components": [
    {"name": "V1", "nodes": ["in", "0"], "value": "AC 1"},
    {"name": "R1", "nodes": ["in", "out"], "value": "1k"},
    {"name": "C1", "nodes": ["out", "0"], "value": "100n"}
  ],
  "directives": [".ac dec 100 1 1meg"]
}

Produces this netlist:

* RC Lowpass Filter

V1 in 0 AC 1
R1 in out 1k
C1 out 0 100n

.ac dec 100 1 1meg
.backanno
.end

And returns:

{
  "success": true,
  "output_path": "/tmp/RC_Lowpass_Filter.cir",
  "netlist_preview": "* RC Lowpass Filter\n\nV1 in 0 AC 1\nR1 in out 1k\nC1 out 0 100n\n\n.ac dec 100 1 1meg\n.backanno\n.end\n",
  "component_count": 3
}

---

create_from_template

Create a circuit netlist from a pre-built template. Each template generates a complete, ready-to-simulate .cir file with default component values that can be selectively overridden. All parameter values are passed as strings.

Available templates:

Template	Description
voltage_divider	Resistive voltage divider with .op or custom analysis
rc_lowpass	RC lowpass filter with AC sweep
inverting_amplifier	Inverting op-amp (gain = -Rf/Rin), +/-15V supply
non_inverting_amplifier	Non-inverting op-amp (gain = 1 + Rf/Rin), +/-15V supply
differential_amplifier	Diff amp: Vout = (R2/R1)(V2-V1), +/-15V supply
common_emitter_amplifier	BJT common-emitter with voltage divider bias
buck_converter	Step-down DC-DC converter with MOSFET switch
ldo_regulator	LDO regulator: Vout = Vref * (1 + R1/R2)
colpitts_oscillator	LC oscillator: f ~ 1/(2 pi sqrt(L Cseries))
h_bridge	4-MOSFET H-bridge motor driver with dead time
sallen_key_lowpass	Sallen-Key lowpass (unity gain, 2nd order)
boost_converter	Step-up DC-DC converter with MOSFET switch
instrumentation_amplifier	3-opamp instrumentation amp: gain = (1 + 2R1/Rgain)(R3/R2)
current_mirror	BJT current mirror with reference resistor
transimpedance_amplifier	TIA: Vout = -Iin * Rf

Parameter	Type	Default	Description
template_name	str	---	Template name from the table above.
params	dict[str, str] | None	None	Optional parameter overrides as key-value string pairs. Use list_templates to see available parameters and defaults for each template.
output_path	str | None	None	Where to save the .cir file. None saves to /tmp/<template_name>.cir.

Returns: A dict with success (boolean), template (name used), description, output_path, netlist_preview (full rendered netlist text), component_count, and params_used (merged defaults and overrides).

Example

{
  "success": true,
  "template": "rc_lowpass",
  "description": "RC lowpass filter with AC sweep",
  "output_path": "/tmp/rc_lowpass.cir",
  "netlist_preview": "* RC Lowpass Filter\n\nV1 in 0 AC 1\nR1 in out 4.7k\nC1 out 0 10n\n\n.ac dec 100 1 1meg\n.backanno\n.end\n",
  "component_count": 3,
  "params_used": {
    "r": "4.7k",
    "c": "10n",
    "f_start": "1",
    "f_stop": "1meg"
  }
}

---

generate_schematic

Generate an LTspice .asc graphical schematic file from a template. Unlike create_from_template which produces a text-based .cir netlist, this tool creates a ready-to-open .asc file with proper component placement, wire routing, net labels, and simulation directives. The output can be loaded directly into the LTspice GUI.

Uses the same template names and parameters as create_from_template.

Parameter	Type	Default	Description
template	str	---	Template name (same set as create_from_template).
params	dict[str, str] | None	None	Optional parameter overrides as key-value string pairs.
output_path	str | None	None	Where to save the .asc file. None saves to /tmp/<template>.asc.

Returns: A dict with success (boolean), output_path (path to the generated .asc file), template (name used), and schematic_preview (first 500 characters of the rendered .asc content).

Example

{
  "success": true,
  "output_path": "/tmp/inverting_amp.asc",
  "template": "inverting_amp",
  "schematic_preview": "Version 4\nSHEET 1 880 680 0\nWIRE 96 192 96 128\nWIRE 96 320 96 256\nWIRE 224 160 160 160\nWIRE 224 224 160 224\n..."
}

---

read_touchstone

Parse a Touchstone (.s1p, .s2p, .snp) S-parameter file. Supports all standard format types (MA, DB, RI), all frequency units (Hz, kHz, MHz, GHz), and any port count. Frequencies are converted to Hz and S-parameters are returned in dB magnitude.

Parameter	Type	Default	Description
file_path	str	---	Path to the Touchstone file (.s1p, .s2p, .s3p, .s4p, etc.).

Returns: A dict with filename, n_ports, n_frequencies (number of frequency points), freq_range_hz (two-element array [min, max]), reference_impedance (ohms), s_parameters (a dict keyed by parameter name like "S11", "S21", each containing a magnitude_db array), and comments (first five comment lines from the file).

Example

{
  "filename": "filter.s2p",
  "n_ports": 2,
  "n_frequencies": 201,
  "freq_range_hz": [100000000.0, 6000000000.0],
  "reference_impedance": 50.0,
  "s_parameters": {
    "S11": {
      "magnitude_db": [-25.3, -24.8, -23.1, "..."]
    },
    "S12": {
      "magnitude_db": [-45.0, -44.2, -43.8, "..."]
    },
    "S21": {
      "magnitude_db": [-0.8, -0.9, -1.2, "..."]
    },
    "S22": {
      "magnitude_db": [-22.1, -21.5, -20.3, "..."]
    }
  },
  "comments": [
    "2-port bandpass filter measurement",
    "VNA: Keysight N5222B",
    "Date: 2025-01-15"
  ]
}