Ltspice Qucs

---

What is mcp-ltspice-qucs?

mcp-ltspice-qucs is a three-server MCP suite plus a shared contracts library, all speaking Touchstone as the cross-tool exchange format. It collapses a typical filter-design loop — hours of LTspice nudging component values, swapping SPICE models, re-running, eyeballing S21 — into an agent-driven iteration at the design intent layer.

Drive it from any MCP client. mcp-ltspice exposes 76 primary tools plus 59 namespaced aliases (filter.*, power.*, analog.*, and others). mcp-qucs-s adds native S-parameter simulation, Xyce harmonic balance, and closed-form microstrip / distributed-filter synthesis with 16 substrate presets. mcp-rf-analysis adds simulator-agnostic skrf wrappers, band databases, FCC / ETSI / 3GPP spec evaluation, and multi-radio coexistence analysis. Selected LC, Qucs-S, and Xyce paths have real-simulator integration tests. Required per-commit CI installs ngspice; the weekly self-hosted matrix executes LTspice, qucsator-RF, and Xyce instead of treating an absent backend as a pass.

What mcp-ltspice-qucs does well:

• AI-native via MCP. Three first-class Model Context Protocol servers. Any MCP agent can iterate filter topologies, sweep vendor parts, and run Monte Carlo yield analyses.
• Real simulator drivers plus fast analytical models. Drives LTspice (native or under Wine), ngspice, Qucs-S / qucsator-RF for native S-parameter simulation, and Xyce for harmonic balance. Selected analytical ladder cases are cross-checked against simulator output.
• Closed-form synthesis and optimization. LC ladders (Butterworth / Chebyshev / elliptic, all of LPF / HPF / BPF / BSF including elliptic band-transforms), Sallen-Key, MFB, Richards-Kuroda, and a complete distributed set: stepped-impedance, edge-coupled, hairpin, interdigital, and combline microstrip filters on an exact coupled-line TEM model.
• Coexistence-driven design. Victim-weighted transmission-zero placement against LTE / 5G NR / GNSS / FCC-restricted bands, a GNSS ΔC/N₀ desense model, and a closed loop that iterates filter order until the coex matrix meets a desense target.
• Circuit-file workbench and model-aware optimization. Supported LTspice ASC, SPICE, Qucs schematic, and Qucsator netlist files import into a connectivity-preserving CircuitDocument 1.0 or return a complete unsupported-construct report. Component search enforces package, availability, ratings, Q/SRF, bias, temperature, and tolerance. Generic IR optimization preserves topology, evaluates corners/yield, instantiates exact selected models, and can require an independent final simulator before reporting simulator_validated.
• CISPR-aware. Conducted and radiated emission prediction against CISPR 22 / 32 and FCC Part 15 limits, anchored to closed-form references, before you build.

---

Quick start

Install

git clone https://github.com/RFingAdam/mcp-ltspice-qucs.git
cd mcp-ltspice-qucs
uv sync --all-packages
uv run pytest -q                  # simulator-gated tests skip when tools are absent
uv run python examples/basic_lpf/design.py

See docs/installation.md for ngspice / LTspice / Qucs-S external-tool setup. The general circuit workbench guide documents file-format boundaries, backend adapters, tolerance policies, component search, and generic optimization.

Wire it into your MCP client

The repository includes a tested Codex project configuration and Claude Code project configuration. Trust the repository in the client, then inspect the three connected servers.

Claude Code:

claude mcp list

Then ask your assistant:

"Synthesize a 5th-order Butterworth LPF at fc = 1 GHz, swap in Coilcraft 0402HP and Murata GJM C0G parts at 5% tolerance, and report yield."

The agent calls synthesize_lc_filter, substitute_real_components, and monte_carlo_analysis in sequence. The bundled LPF's analytical preview reports all 5 spec criteria passing at 99% yield using catalog-snapped ideal values; verify the realized circuit in SPICE before treating that number as production evidence.

---

Tools

mcp-ltspice-qucs ships three MCP servers with 140 primary tools (199 registrations when the 59 deprecated mcp-ltspice aliases are included):

Server	Tools	Purpose
mcp-ltspice	76	LTspice + ngspice. Circuit IR import/export, durable jobs/artifacts, generic model-aware optimization, LC ladder synthesis, coex-driven design, Monte Carlo, SMPS sizing + EMC, active filters, device catalogs
mcp-qucs-s	29	Qucs schematic/netlist IR import/export, durable simulation jobs, native S-param simulation + Xyce harmonic balance, microstrip + 16 substrate presets, couplers, and distributed filters
mcp-rf-analysis	35	Touchstone I/O, skrf wrappers, readiness probing, LTE / 5G NR / ISM / HaLow / GNSS bands, FCC / ETSI / 3GPP eval, coex matrix with GNSS ΔC/N₀ model, victim-weighted zero placement, EMC predictors

The underscore-separated names are canonical. The categorised dotted aliases (filter.*, power.*, analog.*, digital.*, vendor.*, sim.*) are deprecated compatibility names scheduled for removal in 1.0. Full reference in docs/tool-catalog.md + docs/tools/ (one page per server).

---

What it solves

Workflow	Headline tools	Reference
LC ladder filter design	synthesize_lc_filter → place_transmission_zero → substitute_real_components	Butterworth / Chebyshev / Elliptic
Active filter design	sallen_key_low_pass / sallen_key_high_pass / sallen_key_band_pass, mfb_low_pass / mfb_band_pass	Sallen-Key, MFB
SMPS EMC pre-compliance	design_pi_output_filter, predict_conducted_emissions, design_rc_snubber, design_cm_choke	CISPR 22 / CISPR 32
Microstrip + coupler	synthesize_microstrip_line, synthesize_coupler	Hammerstad-Jensen
Monte Carlo yield	monte_carlo_analysis (joblib parallel)	Gaussian component tolerance
Distributed filters	synthesize_stepped_impedance_lpf, synthesize_coupled_line_bpf, synthesize_hairpin_bpf, synthesize_interdigital_bpf, synthesize_combline_bpf	Pozar §8.6-8.7, exact TEM N-line model
Multi-radio coexistence	place_zeros_for_coex → synthesize_for_coex_target → check_coex_matrix (GNSS ΔC/N₀)	3GPP TS 36.101, FCC restricted bands

Five worked examples ship under examples/: basic_lpf, buck_smps, emc_compliance, filter_compare, opamp_filter.

---

Workflows

mcp-ltspice-qucs fits in the following eng-mcp-suite workflow bundles:

• rf-design — closed-form trans-line synthesis (lineforge) + wire-antenna MoM (mcp-nec2-antenna) + circuit/filter sim (this server).
• coexistence-review — multi-radio band picking + filter design against CISPR limits, fed into PCB layout review (mcp-pcb-emcopilot).

See the suite manifest for the full list of sibling MCPs and bundle definitions.

---

Scope and related MCP servers

This suite is circuit-level + filter-synthesis focused. Deliberately stops at the antenna port and at the schematic-to-layout boundary. For:

• Antenna design → mcp-nec2-antenna (wire / MoM) or mcp-openems (FDTD).
• PCB-level EMC / SI / PI → mcp-pcb-emcopilot.
• Regulatory standards lookup → mcp-emc-regulations.
• Physical-layer testing on real hardware → a hardware-DUT MCP.

See docs/related-mcp-servers.md for the full boundary statement, decision flow, and cross-MCP workflow examples.

---

Documentation

• Getting started — install through first call.
• Tool catalog — all 140 primary tools, per-server pages under docs/tools/.
• Backend matrix — runtime readiness and CI validation tiers.
• Migration guide — canonical names, error semantics, jobs, and numerical changes.
• Usage example — practical end-to-end walkthrough.
• Architecture — interop contract between servers.
• Suite architecture — how this MCP fits in eng-mcp-suite.
• Changelog

---

Part of eng-mcp-suite

_{This MCP server is part of}

eng-mcp-suite

_{An open umbrella for engineering MCP servers across RF, EMC, PCB, signal integrity, EM simulation, and lab test. Same brand, same docs structure, designed to compose. See the full catalog or jump to a sibling:}

Domain	Sibling MCPs
RF / Transmission lines	lineforge
Antennas	mcp-nec2-antenna
PCB / SI	mcp-pcb-emcopilot
EMC regulatory	mcp-emc-regulations
EM simulation (3D)	mcp-openems
Diagrams	drawio-engineering-mcp
Lab gear	copper-mountain-vna-mcp

---

Contributing

Contributions are welcome.

1. Pick a GitHub issue.
2. Fork + branch (feature/your-thing or fix/your-bug).
3. Run the local check suite:

   uv sync --all-packages
   uv run pytest -q
   uv run ruff check . && uv run ruff format --check .
   

4. Open a PR — link the issue, request review.

Full contributor guide in CONTRIBUTING.md.

---

License & changelog

AGPL-3.0-or-later; per-release changes in CHANGELOG.md (Keep a Changelog format). Relicensed from Apache-2.0 in v0.4.0 to align with the eng-mcp-suite toolkit-wide AGPL move. Underlying Qucs-S (GPL), LTspice (proprietary), and scikit-rf (BSD) are runtime-invoked dependencies, not redistributed by these wrappers.

Acknowledgments

• LTspice — Analog Devices' SPICE simulator.
• Qucs-S — Quite Universal Circuit Simulator with SPICE-compatible kernels.
• scikit-rf — Touchstone and S-parameter library underneath the analysis layer.
• The MCP working group — for the Model Context Protocol specification.