Add auto-schematic generation from SPICE netlists

Parse netlists into component graphs and render circuit diagrams via SchemDraw. Two layout strategies: loop layout for simple 2-terminal circuits (RC, RL, voltage divider) and labeled grid for complex circuits with active devices (BJT amplifiers, MOSFET). Backend: netlist parser, schematic engine, POST API endpoint. Frontend: SchematicViewer with zoom/download, stacked cell layout showing schematic + SPICE editor + waveform simultaneously.
2026-02-13 06:07:30 -07:00 · 2026-02-13 06:07:30 -07:00 · de7a29c69e
commit de7a29c69e
parent 42f4428295
11 changed files with 944 additions and 16 deletions
--- a/backend/pyproject.toml
+++ b/backend/pyproject.toml
@ -11,6 +11,7 @@ dependencies = [
    "pydantic>=2.0",
    "numpy>=1.24.0",
    "websockets>=12.0",
+    "schemdraw>=0.19",
 ]

 [project.optional-dependencies]
--- a/backend/src/spicebook/engine/schematic.py
+++ b/backend/src/spicebook/engine/schematic.py
@ -0,0 +1,636 @@
+"""Auto-generate circuit schematics from SPICE netlists using SchemDraw.
+
+Pipeline: netlist text → parse → component list → node graph → layout → SVG
+"""
+
+import logging
+from dataclasses import dataclass, field
+
+logger = logging.getLogger(__name__)
+
+
+# ── Data Structures ─────────────────────────────────────────────
+
+
+@dataclass
+class SpiceComponent:
+    """A parsed SPICE netlist component."""
+
+    name: str
+    prefix: str
+    nodes: list[str]
+    value: str = ""
+    model: str = ""
+
+
+@dataclass
+class ParsedNetlist:
+    """Parsed representation of a SPICE netlist."""
+
+    title: str = ""
+    components: list[SpiceComponent] = field(default_factory=list)
+    models: dict[str, str] = field(default_factory=dict)
+
+
+# ── Ground / Supply Detection ───────────────────────────────────
+
+GROUND_NAMES = {"0", "gnd"}
+SUPPLY_NAMES = {"vcc", "vdd", "vee", "vss"}
+
+
+def _is_ground(node: str) -> bool:
+    return node.lower() in GROUND_NAMES
+
+
+def _is_supply(node: str) -> bool:
+    return node.lower() in SUPPLY_NAMES
+
+
+# ── SPICE Netlist Parser ───────────────────────────────────────
+
+
+def parse_netlist(text: str) -> ParsedNetlist:
+    """Parse SPICE netlist text into structured components."""
+    lines = text.split("\n")
+    if not lines:
+        return ParsedNetlist()
+
+    # First non-blank, non-directive line is the title (SPICE convention)
+    title = ""
+    first_content = 0
+    for i, line in enumerate(lines):
+        stripped = line.strip()
+        if stripped and not stripped.startswith(("*", ";", ".")):
+            title = stripped
+            first_content = i + 1
+            break
+
+    # Pre-scan for .model statements to determine BJT/MOSFET polarity
+    models: dict[str, str] = {}
+    for line in lines:
+        stripped = line.strip()
+        if stripped.lower().startswith(".model"):
+            parts = stripped.split()
+            if len(parts) >= 3:
+                model_name = parts[1]
+                model_type = parts[2].split("(")[0].strip().upper()
+                models[model_name] = model_type
+
+    # Merge continuation lines (SPICE + prefix)
+    merged: list[str] = []
+    for line in lines[first_content:]:
+        stripped = line.strip()
+        if not stripped:
+            continue
+        if stripped.startswith("+") and merged:
+            merged[-1] += " " + stripped[1:].strip()
+        else:
+            merged.append(stripped)
+
+    # Parse each line into components
+    components: list[SpiceComponent] = []
+    for line in merged:
+        if line.startswith(("*", ";", "$")):
+            continue
+        if line.startswith("."):
+            continue
+        comp = _parse_component_line(line, models)
+        if comp is not None:
+            components.append(comp)
+
+    return ParsedNetlist(title=title, components=components, models=models)
+
+
+def _parse_component_line(line: str, models: dict[str, str]) -> SpiceComponent | None:
+    """Parse a single SPICE component line."""
+    parts = line.split()
+    if not parts:
+        return None
+
+    name = parts[0]
+    prefix = name[0].upper()
+
+    parsers = {
+        "R": _parse_rcl,
+        "C": _parse_rcl,
+        "L": _parse_rcl,
+        "V": _parse_source,
+        "I": _parse_source,
+        "D": _parse_diode,
+        "Q": _parse_bjt,
+        "M": _parse_mosfet,
+        "X": _parse_subcircuit,
+        "E": _parse_four_node,
+        "G": _parse_four_node,
+        "S": _parse_four_node,
+        "F": _parse_ccxx,
+        "H": _parse_ccxx,
+        "B": _parse_behavioral,
+    }
+
+    parser = parsers.get(prefix)
+    if parser is None:
+        return None
+
+    if prefix in ("Q", "M"):
+        return parser(parts, models)
+    return parser(parts)
+
+
+def _parse_rcl(parts: list[str]) -> SpiceComponent | None:
+    """Parse R, C, L: NAME N+ N- VALUE."""
+    if len(parts) < 4:
+        return None
+    return SpiceComponent(
+        name=parts[0],
+        prefix=parts[0][0].upper(),
+        nodes=[parts[1], parts[2]],
+        value=parts[3],
+    )
+
+
+def _parse_source(parts: list[str]) -> SpiceComponent | None:
+    """Parse V, I: NAME N+ N- [DC val] [AC val] [transient spec]."""
+    if len(parts) < 3:
+        return None
+    return SpiceComponent(
+        name=parts[0],
+        prefix=parts[0][0].upper(),
+        nodes=[parts[1], parts[2]],
+        value=" ".join(parts[3:]) if len(parts) > 3 else "",
+    )
+
+
+def _parse_diode(parts: list[str]) -> SpiceComponent | None:
+    """Parse D: NAME N+ N- MODEL."""
+    if len(parts) < 4:
+        return None
+    return SpiceComponent(
+        name=parts[0], prefix="D",
+        nodes=[parts[1], parts[2]],
+        model=parts[3],
+    )
+
+
+def _parse_bjt(parts: list[str], models: dict[str, str]) -> SpiceComponent | None:
+    """Parse Q: NAME NC NB NE [NS] MODEL."""
+    if len(parts) < 5:
+        return None
+    name = parts[0]
+    # Check if parts[4] is a known model → 3-node form
+    if parts[4] in models:
+        return SpiceComponent(
+            name=name, prefix="Q",
+            nodes=[parts[1], parts[2], parts[3]],
+            model=parts[4],
+        )
+    # 4-node form (with substrate)
+    if len(parts) >= 6:
+        return SpiceComponent(
+            name=name, prefix="Q",
+            nodes=[parts[1], parts[2], parts[3], parts[4]],
+            model=parts[5],
+        )
+    # Default: 3-node
+    return SpiceComponent(
+        name=name, prefix="Q",
+        nodes=[parts[1], parts[2], parts[3]],
+        model=parts[4],
+    )
+
+
+def _parse_mosfet(parts: list[str], models: dict[str, str]) -> SpiceComponent | None:
+    """Parse M: NAME ND NG NS [NB] MODEL."""
+    if len(parts) < 5:
+        return None
+    name = parts[0]
+    # 4-node + model (standard)
+    if len(parts) >= 6 and not any(c in parts[5] for c in "="):
+        return SpiceComponent(
+            name=name, prefix="M",
+            nodes=[parts[1], parts[2], parts[3], parts[4]],
+            model=parts[5],
+        )
+    # 3-node + model
+    return SpiceComponent(
+        name=name, prefix="M",
+        nodes=[parts[1], parts[2], parts[3]],
+        model=parts[4],
+    )
+
+
+def _parse_subcircuit(parts: list[str]) -> SpiceComponent | None:
+    """Parse X: NAME N1 N2 ... SUBCKT_NAME [params]."""
+    if len(parts) < 3:
+        return None
+    # Find where key=value params start
+    param_start = len(parts)
+    for i in range(len(parts) - 1, 0, -1):
+        if "=" in parts[i]:
+            param_start = i
+        else:
+            break
+    tokens = parts[1:param_start]
+    if not tokens:
+        return None
+    return SpiceComponent(
+        name=parts[0], prefix="X",
+        nodes=tokens[:-1] if len(tokens) > 1 else [],
+        model=tokens[-1],
+    )
+
+
+def _parse_four_node(parts: list[str]) -> SpiceComponent | None:
+    """Parse E, G, S: NAME N+ N- NC+ NC- VALUE/MODEL."""
+    if len(parts) < 6:
+        return None
+    return SpiceComponent(
+        name=parts[0], prefix=parts[0][0].upper(),
+        nodes=[parts[1], parts[2], parts[3], parts[4]],
+        value=" ".join(parts[5:]),
+    )
+
+
+def _parse_ccxx(parts: list[str]) -> SpiceComponent | None:
+    """Parse F, H: NAME N+ N- VNAME GAIN."""
+    if len(parts) < 5:
+        return None
+    return SpiceComponent(
+        name=parts[0], prefix=parts[0][0].upper(),
+        nodes=[parts[1], parts[2]],
+        value=" ".join(parts[3:]),
+    )
+
+
+def _parse_behavioral(parts: list[str]) -> SpiceComponent | None:
+    """Parse B: NAME N+ N- V=expr or I=expr."""
+    if len(parts) < 4:
+        return None
+    return SpiceComponent(
+        name=parts[0], prefix="B",
+        nodes=[parts[1], parts[2]],
+        value=" ".join(parts[3:]),
+    )
+
+
+# ── Node Graph ─────────────────────────────────────────────────
+
+
+def _build_node_map(
+    components: list[SpiceComponent],
+) -> dict[str, list[tuple[SpiceComponent, int]]]:
+    """Build node_name → [(component, terminal_index)] adjacency map."""
+    node_map: dict[str, list[tuple[SpiceComponent, int]]] = {}
+    for comp in components:
+        for i, node in enumerate(comp.nodes):
+            node_map.setdefault(node, []).append((comp, i))
+    return node_map
+
+
+# ── Main Loop Finder ───────────────────────────────────────────
+
+
+def _find_main_loop(
+    components: list[SpiceComponent],
+    node_map: dict[str, list[tuple[SpiceComponent, int]]],
+) -> list[SpiceComponent] | None:
+    """Find the main signal loop starting from a voltage/current source.
+
+    Traces through 2-terminal components from the source's positive terminal
+    back to its negative terminal.  Returns the ordered component list, or
+    None if no clear loop exists.
+    """
+    source = next((c for c in components if c.prefix == "V"), None)
+    if source is None:
+        source = next((c for c in components if c.prefix == "I"), None)
+    if source is None:
+        return None
+
+    start_node = source.nodes[0]  # positive terminal
+    end_node = source.nodes[1]  # negative terminal (usually ground)
+
+    visited = {source.name}
+    path = [source]
+    current = start_node
+
+    for _ in range(len(components) + 1):
+        # Reached the negative terminal?
+        if current == end_node:
+            return path
+        if _is_ground(current) and _is_ground(end_node):
+            return path
+
+        # Follow the next unvisited 2-terminal component
+        found = False
+        for comp, term_idx in node_map.get(current, []):
+            if comp.name in visited:
+                continue
+            if len(comp.nodes) != 2:
+                continue
+
+            other_idx = 1 - term_idx
+            visited.add(comp.name)
+            path.append(comp)
+            current = comp.nodes[other_idx]
+            found = True
+            break
+
+        if not found:
+            break
+
+    # Did we end at ground?
+    if _is_ground(current) and _is_ground(end_node):
+        return path
+
+    return path if len(path) > 1 else None
+
+
+# ── Value Formatting ───────────────────────────────────────────
+
+
+def _format_value(value: str) -> str:
+    """Clean up a SPICE value for schematic display."""
+    if not value:
+        return ""
+    v = value.strip()
+    # Simplify source specs for display
+    for prefix in ("DC ", "AC ", "dc ", "ac "):
+        if v.startswith(prefix):
+            v = v[len(prefix):]
+            break
+    # Truncate transient specs (PULSE, SIN, etc.)
+    if len(v) > 20:
+        paren = v.find("(")
+        if paren > 0:
+            v = v[:paren].strip()
+        else:
+            v = v[:20] + "..."
+    return v
+
+
+def _component_label(comp: SpiceComponent) -> str:
+    """Build a display label: name + value or model."""
+    val = _format_value(comp.value)
+    if val:
+        return f"{comp.name}\n{val}"
+    if comp.model:
+        return f"{comp.name}\n{comp.model}"
+    return comp.name
+
+
+# ── SchemDraw Element Mapping ──────────────────────────────────
+
+
+def _get_element(comp: SpiceComponent, models: dict[str, str]):
+    """Map a SPICE component prefix to the corresponding SchemDraw element."""
+    import schemdraw.elements as elm
+
+    prefix = comp.prefix
+
+    if prefix == "R":
+        return elm.Resistor()
+    elif prefix == "C":
+        return elm.Capacitor()
+    elif prefix == "L":
+        return elm.Inductor2()
+    elif prefix == "V":
+        return elm.SourceV()
+    elif prefix == "I":
+        return elm.SourceI()
+    elif prefix == "D":
+        return elm.Diode()
+    elif prefix == "Q":
+        model_type = models.get(comp.model, "").upper()
+        if "PNP" in model_type:
+            return elm.BjtPnp()
+        return elm.BjtNpn()
+    elif prefix == "M":
+        model_type = models.get(comp.model, "").upper()
+        if "PMOS" in model_type or model_type == "P":
+            return elm.PFet()
+        return elm.NFet()
+    elif prefix in ("E", "G"):
+        return elm.SourceControlledV()
+    elif prefix in ("F", "H"):
+        return elm.SourceControlledI()
+    elif prefix == "S":
+        return elm.Switch()
+    else:
+        return elm.RBox()
+
+
+# ── Loop Layout Renderer ──────────────────────────────────────
+
+
+def _render_loop(parsed: ParsedNetlist, loop: list[SpiceComponent]) -> str:
+    """Render a simple circuit loop as a clean rectangular schematic.
+
+    Layout: source on the left going up, components across the top going
+    right, last component going down on the right, return wire along the
+    bottom with a ground symbol.
+    """
+    import schemdraw
+    import schemdraw.elements as elm
+
+    d = schemdraw.Drawing(fontsize=12)
+
+    source = loop[0]
+    path_comps = loop[1:]
+
+    if not path_comps:
+        # Standalone source
+        d.add(
+            _get_element(source, parsed.models)
+            .up()
+            .label(_component_label(source), loc="left")
+        )
+        d.add(elm.Ground())
+        return d.get_imagedata("svg").decode()
+
+    # Source on left side, going up
+    src = d.add(
+        _get_element(source, parsed.models)
+        .up()
+        .label(_component_label(source), loc="left")
+    )
+
+    # All components except the last go right across the top
+    for comp in path_comps[:-1]:
+        d.add(
+            _get_element(comp, parsed.models)
+            .right()
+            .label(_component_label(comp))
+        )
+
+    # Last component goes down, ending at the same y-level as the source start
+    last_comp = path_comps[-1]
+    d.add(
+        _get_element(last_comp, parsed.models)
+        .down()
+        .toy(src.start)
+        .label(_component_label(last_comp), loc="right")
+    )
+
+    # Return wire along the bottom back to source start
+    d.add(elm.Line().to(src.start))
+
+    # Ground symbol at the source's negative terminal
+    d.add(elm.Ground().at(src.start))
+
+    # Node label at source positive terminal
+    node_label = source.nodes[0]
+    if not _is_ground(node_label):
+        d.add(
+            elm.Dot(open=True)
+            .at(src.end)
+            .label(node_label, loc="left", fontsize=9)
+        )
+
+    # Node label at junction between top components and the last (shunt) component
+    if len(path_comps) >= 2:
+        junction_node = path_comps[-2].nodes[1] if len(path_comps[-2].nodes) >= 2 else ""
+        if junction_node and not _is_ground(junction_node):
+            # Find the end of the second-to-last component (the junction point)
+            # SchemDraw doesn't give us this easily, so skip for now
+            pass
+
+    return d.get_imagedata("svg").decode()
+
+
+# ── Grid Layout Renderer ──────────────────────────────────────
+
+
+def _render_grid(parsed: ParsedNetlist) -> str:
+    """Render components in a labeled grid layout.
+
+    Used for complex circuits where topological layout isn't feasible.
+    Components are arranged in columns by type with terminal node labels.
+    """
+    import schemdraw
+
+    d = schemdraw.Drawing(fontsize=11)
+
+    # Group by role for logical ordering
+    sources = [c for c in parsed.components if c.prefix in ("V", "I")]
+    passives = [c for c in parsed.components if c.prefix in ("R", "C", "L")]
+    active = [c for c in parsed.components if c.prefix in ("D", "Q", "M")]
+    other = [
+        c for c in parsed.components
+        if c.prefix not in ("V", "I", "R", "C", "L", "D", "Q", "M")
+    ]
+    ordered = sources + passives + active + other
+
+    cols = min(4, max(2, len(ordered)))
+    x_spacing = 8
+    y_spacing = 5
+
+    for i, comp in enumerate(ordered):
+        row = i // cols
+        col = i % cols
+        x = col * x_spacing
+        y = -row * y_spacing
+
+        elem = _get_element(comp, parsed.models)
+
+        # 3+ terminal devices (BJT, MOSFET) need special handling
+        if comp.prefix in ("Q", "M") and len(comp.nodes) >= 3:
+            placed = d.add(elem.at((x, y)).label(_component_label(comp)))
+            _label_multiterminal(d, placed, comp)
+        else:
+            placed = d.add(
+                elem.at((x, y)).right().label(_component_label(comp))
+            )
+            _label_two_terminal(d, placed, comp)
+
+    return d.get_imagedata("svg").decode()
+
+
+def _label_two_terminal(d, placed, comp: SpiceComponent) -> None:
+    """Add node-name labels to a placed 2-terminal element."""
+    import schemdraw.elements as elm
+
+    if len(comp.nodes) >= 1:
+        d.add(elm.Dot(radius=0.08).at(placed.start))
+        d.add(
+            elm.Label()
+            .at(placed.start)
+            .label(comp.nodes[0], loc="left", fontsize=8)
+        )
+    if len(comp.nodes) >= 2:
+        d.add(elm.Dot(radius=0.08).at(placed.end))
+        d.add(
+            elm.Label()
+            .at(placed.end)
+            .label(comp.nodes[1], loc="right", fontsize=8)
+        )
+
+
+def _label_multiterminal(d, placed, comp: SpiceComponent) -> None:
+    """Add node-name labels to a placed multi-terminal element (BJT/MOSFET)."""
+    import schemdraw.elements as elm
+
+    terminal_names = {
+        "Q": ["C", "B", "E"],
+        "M": ["D", "G", "S"],
+    }
+    anchor_map_q = ["collector", "base", "emitter"]
+    anchor_map_m = ["drain", "gate", "source"]
+
+    anchors = anchor_map_q if comp.prefix == "Q" else anchor_map_m
+    labels = terminal_names.get(comp.prefix, [])
+
+    for j, node in enumerate(comp.nodes[:3]):
+        if j < len(anchors) and hasattr(placed, anchors[j]):
+            pos = getattr(placed, anchors[j])
+            d.add(elm.Dot(radius=0.08).at(pos))
+            label_text = f"{labels[j]}:{node}" if j < len(labels) else node
+            d.add(
+                elm.Label()
+                .at(pos)
+                .label(label_text, fontsize=8)
+            )
+
+
+# ── Public API ─────────────────────────────────────────────────
+
+
+def netlist_to_svg(netlist_text: str) -> str:
+    """Convert a SPICE netlist to an SVG schematic diagram.
+
+    Tries a clean loop layout for simple circuits (<=12 two-terminal
+    components with a clear main path), falls back to a labeled grid
+    for complex circuits with active devices.
+
+    Returns:
+        SVG string.
+
+    Raises:
+        ValueError: If no components could be parsed from the netlist.
+        RuntimeError: If schemdraw is not installed.
+    """
+    try:
+        import schemdraw  # noqa: F401
+    except ImportError:
+        raise RuntimeError(
+            "schemdraw is required for schematic generation. "
+            "Install with: pip install 'schemdraw>=0.19'"
+        )
+
+    parsed = parse_netlist(netlist_text)
+
+    if not parsed.components:
+        raise ValueError("No components found in netlist")
+
+    node_map = _build_node_map(parsed.components)
+
+    # Try loop layout for simple circuits with a clear main path
+    two_terminal_only = all(len(c.nodes) == 2 for c in parsed.components)
+    if two_terminal_only and len(parsed.components) <= 12:
+        loop = _find_main_loop(parsed.components, node_map)
+        if loop and len(loop) >= 2:
+            try:
+                return _render_loop(parsed, loop)
+            except Exception as exc:
+                logger.warning("Loop layout failed, using grid: %s", exc)
+
+    return _render_grid(parsed)
--- a/backend/src/spicebook/main.py
+++ b/backend/src/spicebook/main.py
@ -9,7 +9,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware

 from spicebook.config import settings
-from spicebook.routers import notebooks, simulation, waveforms
+from spicebook.routers import notebooks, schematics, simulation, waveforms

 logger = logging.getLogger("spicebook")

@ -27,9 +27,11 @@ def create_app() -> FastAPI:
        allow_origins=[
            "http://localhost:4321",
            "http://localhost:4322",
+            "http://localhost:4326",
            "http://localhost:3000",
            "http://127.0.0.1:4321",
            "http://127.0.0.1:4322",
+            "http://127.0.0.1:4326",
            "http://127.0.0.1:3000",
        ],
        allow_credentials=True,
@ -38,6 +40,7 @@ def create_app() -> FastAPI:
    )

    application.include_router(notebooks.router)
+    application.include_router(schematics.router)
    application.include_router(simulation.router)
    application.include_router(waveforms.router)

--- a/backend/src/spicebook/routers/schematics.py
+++ b/backend/src/spicebook/routers/schematics.py
@ -0,0 +1,66 @@
+"""Schematic generation endpoints."""
+
+from datetime import datetime, timezone
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel
+
+from spicebook.config import settings
+from spicebook.engine.schematic import netlist_to_svg
+from spicebook.models.notebook import CellOutput, CellType
+from spicebook.storage.filesystem import load_notebook, save_notebook
+
+router = APIRouter(prefix="/api", tags=["schematics"])
+
+
+class SchematicResponse(BaseModel):
+    svg: str | None = None
+    success: bool
+    error: str | None = None
+
+
+@router.post(
+    "/notebooks/{notebook_id}/cells/{cell_id}/schematic",
+    response_model=SchematicResponse,
+)
+async def generate_schematic(notebook_id: str, cell_id: str):
+    """Generate an SVG schematic from a SPICE cell's netlist."""
+    nb = load_notebook(settings.notebook_dir, notebook_id)
+    if nb is None:
+        raise HTTPException(status_code=404, detail=f"Notebook '{notebook_id}' not found")
+
+    cell = next((c for c in nb.cells if c.id == cell_id), None)
+    if cell is None:
+        raise HTTPException(status_code=404, detail=f"Cell '{cell_id}' not found")
+
+    if cell.type != CellType.SPICE:
+        raise HTTPException(
+            status_code=400,
+            detail=f"Cell is type '{cell.type.value}', not 'spice'",
+        )
+
+    if not cell.source.strip():
+        raise HTTPException(status_code=400, detail="Cell source is empty")
+
+    try:
+        svg = netlist_to_svg(cell.source)
+    except (ValueError, RuntimeError) as exc:
+        return SchematicResponse(success=False, error=str(exc))
+    except Exception as exc:
+        return SchematicResponse(success=False, error=f"Schematic generation failed: {exc}")
+
+    # Save schematic output to cell (additive — preserve simulation outputs)
+    now_iso = datetime.now(timezone.utc).isoformat()
+    schematic_output = CellOutput(
+        output_type="schematic",
+        data={"svg": svg, "success": True},
+        timestamp=now_iso,
+    )
+
+    # Remove any previous schematic output, keep everything else
+    cell.outputs = [o for o in cell.outputs if o.output_type != "schematic"]
+    cell.outputs.append(schematic_output)
+
+    save_notebook(settings.notebook_dir, notebook_id, nb)
+
+    return SchematicResponse(svg=svg, success=True)
--- a/backend/src/spicebook/routers/simulation.py
+++ b/backend/src/spicebook/routers/simulation.py
@ -66,10 +66,10 @@ async def run_cell(notebook_id: str, cell_id: str):
    with tempfile.TemporaryDirectory(prefix="spicebook-sim-") as tmpdir:
        result = await engine.run(cell.source, Path(tmpdir))

-    # Save output to the cell in same format the frontend expects
+    # Save output to the cell (preserve schematic outputs across re-runs)
    now_iso = datetime.now(timezone.utc).isoformat()

-    cell.outputs = [CellOutput(
+    sim_output = CellOutput(
        output_type="simulation_result" if result.success else "error",
        data={
            "success": result.success,
@ -79,7 +79,9 @@ async def run_cell(notebook_id: str, cell_id: str):
            "elapsed_seconds": result.elapsed_seconds,
        },
        timestamp=now_iso,
-    )]
+    )
+    preserved = [o for o in cell.outputs if o.output_type == "schematic"]
+    cell.outputs = [sim_output] + preserved

    save_notebook(settings.notebook_dir, notebook_id, nb)

--- a/backend/uv.lock
+++ b/backend/uv.lock
@ -446,6 +446,15 @@ wheels = [
    { url = "https://files.pythonhosted.org/packages/2a/07/5bda6a85b220c64c65686bc85bd0bbb23b29c62b3a9f9433fa55f17cda93/ruff-0.15.1-py3-none-win_arm64.whl", hash = "sha256:5ff7d5f0f88567850f45081fac8f4ec212be8d0b963e385c3f7d0d2eb4899416", size = 10874604, upload-time = "2026-02-12T23:09:05.515Z" },
 ]

+[[package]]
+name = "schemdraw"
+version = "0.22"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/6a/0e/3d2a9c2541ced42877e8b6049fb17c093329ccb81344529dc12a33d4c118/schemdraw-0.22.tar.gz", hash = "sha256:59d1fcfe817f93f8bfc37a3f4645186dc03316bbcfd9ac68804fd6cb3aa69f51", size = 10881350, upload-time = "2025-11-30T23:45:03.279Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/a0/ab/b281071bc11555670a82c538e4be35e7f5ad5e4cb4de7ac356a05a4b2c6a/schemdraw-0.22-py3-none-any.whl", hash = "sha256:fb294fe086b89a7dc9bedce43dc39014a9b9e369864eab438f22009c9f0e1175", size = 148359, upload-time = "2025-11-30T23:42:04.794Z" },
+]
+
 [[package]]
 name = "spicebook"
 version = "2026.2.13"
@ -454,6 +463,7 @@ dependencies = [
    { name = "fastapi" },
    { name = "numpy" },
    { name = "pydantic" },
+    { name = "schemdraw" },
    { name = "uvicorn", extra = ["standard"] },
    { name = "websockets" },
 ]
@ -475,6 +485,7 @@ requires-dist = [
    { name = "pytest", marker = "extra == 'dev'", specifier = ">=8.0" },
    { name = "pytest-asyncio", marker = "extra == 'dev'", specifier = ">=0.23" },
    { name = "ruff", marker = "extra == 'dev'", specifier = ">=0.8" },
+    { name = "schemdraw", specifier = ">=0.19" },
    { name = "uvicorn", extras = ["standard"], specifier = ">=0.30.0" },
    { name = "websockets", specifier = ">=12.0" },
 ]
--- a/frontend/src/components/notebook/cells/SpiceCell.tsx
+++ b/frontend/src/components/notebook/cells/SpiceCell.tsx
@ -5,6 +5,7 @@ import { useNotebookStore } from '../../../lib/notebook-store';
 import { CellToolbar } from '../toolbar/CellToolbar';
 import { SpiceEditor } from '../editor/SpiceEditor';
 import { WaveformViewer } from '../output/WaveformViewer';
+import { SchematicViewer } from '../output/SchematicViewer';
 import { SimulationLog } from '../output/SimulationLog';
 import { cn } from '../../../lib/cn';

@ -23,6 +24,7 @@ export function SpiceCell({ cell, isFirst, isLast }: SpiceCellProps) {
    deleteCell,
    moveCell,
    runCell,
+    generateSchematic,
  } = useNotebookStore();

  const isActive = activeCell === cell.id;
@ -39,9 +41,15 @@ export function SpiceCell({ cell, isFirst, isLast }: SpiceCellProps) {
    runCell(cell.id);
  }, [cell.id, runCell]);

-  // Extract output data
-  const lastOutput = cell.outputs.length > 0 ? cell.outputs[cell.outputs.length - 1] : null;
-  const outputData = lastOutput?.data as {
+  const handleGenerateSchematic = useCallback(() => {
+    generateSchematic(cell.id);
+  }, [cell.id, generateSchematic]);
+
+  // Extract simulation output
+  const simOutput = cell.outputs.find(
+    (o) => o.output_type === 'simulation_result' || o.output_type === 'error',
+  );
+  const outputData = simOutput?.data as {
    success?: boolean;
    waveform?: WaveformData | null;
    log?: string;
@ -49,6 +57,10 @@ export function SpiceCell({ cell, isFirst, isLast }: SpiceCellProps) {
    elapsed_seconds?: number;
  } | null;

+  // Extract schematic output
+  const schematicOutput = cell.outputs.find((o) => o.output_type === 'schematic');
+  const schematicSvg = schematicOutput?.data?.svg as string | null;
+
  return (
    <div
      className={cn(
@ -66,12 +78,20 @@ export function SpiceCell({ cell, isFirst, isLast }: SpiceCellProps) {
        isFirst={isFirst}
        isLast={isLast}
        onRun={handleRun}
+        onGenerateSchematic={handleGenerateSchematic}
        onDelete={() => deleteCell(cell.id)}
        onMoveUp={() => moveCell(cell.id, 'up')}
        onMoveDown={() => moveCell(cell.id, 'down')}
      />

-      {/* Editor */}
+      {/* Schematic — shown above the editor when generated */}
+      {schematicSvg && (
+        <div className="border-b border-slate-700/50">
+          <SchematicViewer svg={schematicSvg} />
+        </div>
+      )}
+
+      {/* SPICE Editor — always visible */}
      <div className="min-h-[80px]">
        <SpiceEditor
          value={cell.source}
@ -85,12 +105,12 @@ export function SpiceCell({ cell, isFirst, isLast }: SpiceCellProps) {
        <div className="border-t border-slate-700/50 px-4 py-3">
          <div className="flex items-center gap-2 text-sm text-blue-400">
            <div className="w-4 h-4 border-2 border-blue-400/30 border-t-blue-400 rounded-full animate-spin" />
-            Running simulation...
+            Processing...
          </div>
        </div>
      )}

-      {/* Outputs */}
+      {/* Waveform + Simulation results — shown below the editor */}
      {!isRunning && outputData && (
        <div className="border-t border-slate-700/50">
          {/* Error banner */}
--- a/frontend/src/components/notebook/output/SchematicViewer.tsx
+++ b/frontend/src/components/notebook/output/SchematicViewer.tsx
@ -0,0 +1,96 @@
+import { useState, useRef, useCallback } from 'react';
+import { ZoomIn, ZoomOut, Maximize2, Download } from 'lucide-react';
+
+interface SchematicViewerProps {
+  svg: string;
+}
+
+const ZOOM_STEPS = [0.5, 0.75, 1.0, 1.25, 1.5, 2.0];
+
+export function SchematicViewer({ svg }: SchematicViewerProps) {
+  const [zoomIndex, setZoomIndex] = useState(2); // Start at 100%
+  const containerRef = useRef<HTMLDivElement>(null);
+
+  const zoom = ZOOM_STEPS[zoomIndex];
+
+  const zoomIn = useCallback(() => {
+    setZoomIndex((i) => Math.min(i + 1, ZOOM_STEPS.length - 1));
+  }, []);
+
+  const zoomOut = useCallback(() => {
+    setZoomIndex((i) => Math.max(i - 1, 0));
+  }, []);
+
+  const fitToWidth = useCallback(() => {
+    setZoomIndex(2); // Reset to 100%
+  }, []);
+
+  const downloadSvg = useCallback(() => {
+    const blob = new Blob([svg], { type: 'image/svg+xml' });
+    const url = URL.createObjectURL(blob);
+    const a = document.createElement('a');
+    a.href = url;
+    a.download = 'schematic.svg';
+    a.click();
+    URL.revokeObjectURL(url);
+  }, [svg]);
+
+  return (
+    <div className="relative">
+      {/* Toolbar */}
+      <div className="flex items-center gap-1 px-3 py-1.5 border-b border-slate-700/50 bg-slate-800/50">
+        <button
+          onClick={zoomOut}
+          disabled={zoomIndex === 0}
+          className="p-1 rounded text-slate-400 hover:text-slate-200 hover:bg-slate-700/50 disabled:opacity-30 disabled:cursor-not-allowed transition-colors"
+          title="Zoom out"
+        >
+          <ZoomOut className="w-3.5 h-3.5" />
+        </button>
+        <span className="text-xs text-slate-500 tabular-nums w-10 text-center">
+          {Math.round(zoom * 100)}%
+        </span>
+        <button
+          onClick={zoomIn}
+          disabled={zoomIndex === ZOOM_STEPS.length - 1}
+          className="p-1 rounded text-slate-400 hover:text-slate-200 hover:bg-slate-700/50 disabled:opacity-30 disabled:cursor-not-allowed transition-colors"
+          title="Zoom in"
+        >
+          <ZoomIn className="w-3.5 h-3.5" />
+        </button>
+        <button
+          onClick={fitToWidth}
+          className="p-1 rounded text-slate-400 hover:text-slate-200 hover:bg-slate-700/50 transition-colors"
+          title="Reset zoom"
+        >
+          <Maximize2 className="w-3.5 h-3.5" />
+        </button>
+        <div className="flex-1" />
+        <button
+          onClick={downloadSvg}
+          className="flex items-center gap-1 px-2 py-1 rounded text-xs text-slate-400 hover:text-slate-200 hover:bg-slate-700/50 transition-colors"
+          title="Download SVG"
+        >
+          <Download className="w-3.5 h-3.5" />
+          <span>SVG</span>
+        </button>
+      </div>
+
+      {/* SVG Canvas */}
+      <div
+        ref={containerRef}
+        className="overflow-auto bg-white rounded-b-lg"
+        style={{ maxHeight: '500px' }}
+      >
+        <div
+          className="p-4"
+          style={{
+            transform: `scale(${zoom})`,
+            transformOrigin: 'top left',
+          }}
+          dangerouslySetInnerHTML={{ __html: svg }}
+        />
+      </div>
+    </div>
+  );
+}
--- a/frontend/src/components/notebook/toolbar/CellToolbar.tsx
+++ b/frontend/src/components/notebook/toolbar/CellToolbar.tsx
@ -8,6 +8,7 @@ import {
  Zap,
  Code,
  Image,
+  CircuitBoard,
 } from 'lucide-react';
 import { Button } from '../../ui/Button';
 import { Badge } from '../../ui/Badge';
@ -20,6 +21,7 @@ interface CellToolbarProps {
  isFirst: boolean;
  isLast: boolean;
  onRun?: () => void;
+  onGenerateSchematic?: () => void;
  onDelete: () => void;
  onMoveUp: () => void;
  onMoveDown: () => void;
@ -58,6 +60,7 @@ export function CellToolbar({
  isFirst,
  isLast,
  onRun,
+  onGenerateSchematic,
  onDelete,
  onMoveUp,
  onMoveDown,
@ -80,6 +83,19 @@ export function CellToolbar({
      {/* Cell ID */}
      <span className="text-[10px] text-slate-600 font-mono mr-2">{cellId}</span>

+      {/* Generate schematic (SPICE cells only) */}
+      {onGenerateSchematic && (
+        <Button
+          variant="ghost"
+          size="icon"
+          onClick={onGenerateSchematic}
+          disabled={isRunning}
+          title="Generate schematic from netlist"
+        >
+          <CircuitBoard className="w-3.5 h-3.5 text-cyan-400" />
+        </Button>
+      )}
+
      {/* Run button (SPICE cells only) */}
      {onRun && (
        <Button
--- a/frontend/src/lib/api.ts
+++ b/frontend/src/lib/api.ts
@ -170,3 +170,23 @@ export async function runCell(
    },
  );
 }
+
+// ── Schematics ────────────────────────────────────────────────
+
+export interface SchematicResponse {
+  svg: string | null;
+  success: boolean;
+  error?: string;
+}
+
+export async function generateSchematic(
+  notebookId: string,
+  cellId: string,
+): Promise<SchematicResponse> {
+  return request<SchematicResponse>(
+    `/api/notebooks/${encodeURIComponent(notebookId)}/cells/${encodeURIComponent(cellId)}/schematic`,
+    {
+      method: 'POST',
+    },
+  );
+}
--- a/frontend/src/lib/notebook-store.ts
+++ b/frontend/src/lib/notebook-store.ts
@ -49,6 +49,7 @@ interface NotebookStore {
  setActiveCell: (cellId: string | null) => void;
  runCell: (cellId: string) => Promise<void>;
  runAllCells: () => Promise<void>;
+  generateSchematic: (cellId: string) => Promise<void>;
  setCellOutput: (cellId: string, output: CellOutput) => void;
  updateTitle: (title: string) => void;
  updateEngine: (engine: string) => void;
@ -222,9 +223,12 @@ export const useNotebookStore = create<NotebookStore>((set, get) => ({
        set({
          notebook: {
            ...updatedNotebook,
-            cells: updatedNotebook.cells.map((c) =>
-              c.id === cellId ? { ...c, outputs: [output] } : c,
-            ),
+            cells: updatedNotebook.cells.map((c) => {
+              if (c.id !== cellId) return c;
+              // Preserve schematic outputs across simulation re-runs
+              const preserved = c.outputs.filter((o) => o.output_type === 'schematic');
+              return { ...c, outputs: [output, ...preserved] };
+            }),
          },
        });
      }
@ -245,9 +249,11 @@ export const useNotebookStore = create<NotebookStore>((set, get) => ({
        set({
          notebook: {
            ...updatedNotebook,
-            cells: updatedNotebook.cells.map((c) =>
-              c.id === cellId ? { ...c, outputs: [output] } : c,
-            ),
+            cells: updatedNotebook.cells.map((c) => {
+              if (c.id !== cellId) return c;
+              const preserved = c.outputs.filter((o) => o.output_type === 'schematic');
+              return { ...c, outputs: [output, ...preserved] };
+            }),
          },
        });
      }
@ -258,6 +264,57 @@ export const useNotebookStore = create<NotebookStore>((set, get) => ({
    }
  },

+  generateSchematic: async (cellId: string) => {
+    const { notebook, notebookId, runningCells } = get();
+    if (!notebook || !notebookId) return;
+
+    const cell = notebook.cells.find((c) => c.id === cellId);
+    if (!cell || cell.type !== 'spice') return;
+
+    const newRunning = new Set(runningCells);
+    newRunning.add(cellId);
+    set({ runningCells: newRunning });
+
+    try {
+      const result = await api.generateSchematic(notebookId, cellId);
+
+      if (result.success && result.svg) {
+        const output: CellOutput = {
+          output_type: 'schematic',
+          data: { svg: result.svg, success: true },
+          timestamp: new Date().toISOString(),
+        };
+
+        const updatedNotebook = get().notebook;
+        if (updatedNotebook) {
+          set({
+            notebook: {
+              ...updatedNotebook,
+              cells: updatedNotebook.cells.map((c) => {
+                if (c.id !== cellId) return c;
+                // Replace existing schematic, keep everything else
+                const others = c.outputs.filter((o) => o.output_type !== 'schematic');
+                return { ...c, outputs: [...others, output] };
+              }),
+            },
+          });
+        }
+      } else {
+        set({
+          error: result.error || 'Schematic generation failed',
+        });
+      }
+    } catch (err) {
+      set({
+        error: err instanceof Error ? err.message : 'Schematic generation failed',
+      });
+    } finally {
+      const currentRunning = new Set(get().runningCells);
+      currentRunning.delete(cellId);
+      set({ runningCells: currentRunning });
+    }
+  },
+
  runAllCells: async () => {
    const { notebook } = get();
    if (!notebook) return;