Rftools

rftools-mcp

MCP server for [rftools.io](https://rftools.io) — 255 RF & electronics calculators + 13 server-side simulation tools for AI agents.

Give Claude, Cursor, or any MCP-compatible AI assistant access to validated engineering calculators and heavy server-side simulations. Microstrip impedance, link budgets, filter design, converter sizing, antenna patterns, and 200+ more calculators — plus NEC2 antenna simulation, FDTD, Monte Carlo, SMPS analysis, EMI estimation, and more, all callable as MCP tools.

Quick Start

Calculators work with no API key, and so do the simulation tools: without one, a job runs on the free lane. A key raises the limits — sign up at rftools.io and generate one from your dashboard. The one thing a key is required for is a file: uploading a file needs an API key; set RFTOOLS_API_KEY.

Setup

Without API key

All 255 calculators run locally with no sign-up required, and every simulation tool that takes no file still submits — on the free lane, with the free limits and the free-lane parameter bounds stated on the response.

A job type that takes a file is the exception. Uploading a file needs an API key; set RFTOOLS_API_KEY. Without one, a call carrying inputFiles or inputPaths is refused here, with that sentence, before the file is read and before any request leaves this machine.

With API key

Sign up at rftools.io and generate an API key from your dashboard. Free accounts include 5 simulation runs/month. Pro: 100/month. API tier: 10,000/month. A paid key also unlocks the modes the free lane cannot run: the antenna optimiser and the FDTD normal and fine meshes.

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{

"mcpServers": { "rftools": { "command": "npx", "args": ["-y", "rftools-mcp"], "env": { "RFTOOLS_API_KEY": "rfc_your_key_here" } } } }

Omit the env block to use calculators only. Restart Claude Desktop after saving.

Claude Code

claude mcp add rftools-mcp -- npx -y rftools-mcp

To add your API key:

claude mcp add rftools-mcp -e RFTOOLS_API_KEY=rfc_your_key_here -- npx -y rftools-mcp

Cursor

Add to .cursor/mcp.json in your project:

{

"mcpServers": { "rftools": { "command": "npx", "args": ["-y", "rftools-mcp"], "env": { "RFTOOLS_API_KEY": "rfc_your_key_here" } } } }

Windsurf

Add to ~/.codeium/windsurf/mcp_config.json:

{

"mcpServers": { "rftools": { "command": "npx", "args": ["-y", "rftools-mcp"], "env": { "RFTOOLS_API_KEY": "rfc_your_key_here" } } } }

Tools

24 tools: six for calculators, one simulate_* tool for each of the 13 job types, and five for the job lifecycle; plus the site's reference tables as resources.

What changed in 2.5.7

No tool changed. Results follow rftools.io's trace thermal model (changelog, 2026-10-14):

• `trace-width-current` gains `widthBoardMm` and `pcb-trace-temp` gains `tempRiseBoard` and `maxTempBoard`: the width and rise for this board, from rftools' own thermal model (never labelled IPC-2152), with inModelRange and a 15 % margin. New optional inputs: boardThickness, planeDistance, planeCopperWeight (and isExternal on pcb-trace-temp).
• `provenance.validRange.models` lists both fitted models on these two calculators, each with its own inside.
• Both calculators refuse a zero or negative current, rise, copper weight or length, as the API does.

What changed in 2.5.6

No tool changed. simulate_emi_radiated's fields now use the exact π·µ₀/c and µ₀ (once the worker deploys), and calculator results follow the rftools.io formula follow-up (changelog, 2026-10-13):

• Seven outputs are removed (breaking): differential-via's five impedances (a field solution showed they depend on the plane pitch, which is not an input), usb-termination eyeOpening and parabolic-dish-antenna noiseTemperature.
• Values that do not exist are null (breaking): USB 3.0 rise time, crosstalk above the weak-coupling limit, sealed subwoofer at Qts ≥ 0.707, spiral Q at or above resonance, a lossless LC circuit's Q, a via with no stub; and a refused input returns no values instead of zeros.
• Models corrected: the planar spiral's self-resonance and Q, Paul's two-end crosstalk with a far-end output, Margolis & Small port tuning, coupled-microstrip pcb-crosstalk, Balanis' slot model for the patch, LC Q in parallel mode plus the impedance at resonance, microvia arrays, via self-heating, BGA escape rows, IPC-2222 aspect ratios.
• Exact constants: one η₀ = µ₀·c, η₀/2π in every microstrip impedance (−0.069 %), and IEC 60028 copper.
• New inputs: planar-spiral-inductor frequency, pcb-crosstalk dielectricConst, aperture-diagonal routerBit.

What changed in 2.5.5

No tool or argument changed. Calculator inputs and outputs follow the rftools.io input audit (changelog, 2026-10-12):

• Twelve inputs that never changed a result are retired: a call that still sends one is computed and answered with the warning "Input 'X' is not read by this calculator and was ignored." (get_calculator_schema no longer lists them).
• Eight inputs now drive new outputs: patch-antenna's feed resistance at the inset, flyback's primary inductance, solar autonomy, the RS-485 baud rate against the cable's maximum, the ADC's Nyquist zone and alias, bldc-thermal's share of the rating, bldc-winding's no-load speed, and the ISM band. Yagi reports assumedBoomLength.
• Four constant outputs are removed (breaking): balun-transformer vswr and insertionLoss, opamp-bandwidth slewLimited, capacitor-code voltageCode.
• `loop-antenna`'s gain includes its radiation efficiency (it always read 1.76 dBi); a radiationEfficiency output is added.

What changed in 2.5.4

No tool or name changed. trace-width-current's IPC-2152 width (width2152mm) is now IPC-2152 Figure 5-1 (the conservative chart, by its published closed form) instead of IPC-2221 × 0.75/0.85, which erred on the unsafe side: 5 A at a 10 °C rise in 1 oz copper needs 7.19 mm, not 2.09 mm. A new optional traceWidth input sets the width that resistance, voltage drop and power are computed at. pcb-trace-temp adds the Figure 5-1 rise and maximum temperature (rftools.io changelog, 2026-10-12).

What changed in 2.5.3

No tool, argument or name changed. Twelve calculators now compute the model they cite (rftools.io changelog, 2026-10-12):

• mosfet-operating-point solves the drain load line (11.96 mA at the defaults, not 450 mA; biasMode 1 keeps the entered V_DS);
• radar-range-equation takes the range at the required SNR (Albersheim, new pd, pfa and pulses inputs);
• cable-shield-effectiveness refers the shielding to a 50 Ω line;
• ferrite-bead uses a complex bead model (AN-1368);
• bldc-motor solves the loaded speed;
• ethernet-cable uses TIA-568-C.2 insertion loss at each PHY's signalling frequency (Category 8 on IEEE 802.3bq draft coefficients);
• bldc-efficiency and bldc-thermal take I²·R copper loss, and bldc-thermal's hot resistance (it is null above the runaway current);
• class-d-efficiency and motor-driver-power count two conducting FETs;
• coax-impedance and via-calculator use η₀/2π.

What changed in 2.5.2

No tool, argument or name changed. bldc-winding now counts both coil sides in each slot (a double-layer winding), so its fill factor is 2·N·A_wire/A_slot and is no longer capped at 100 %. Its distribution factor comes from the star-of-slots method (12N14P: 0.933, not 0.966), and its default maximum current is 5 A, a winding that builds (rftools.io changelog, 2026-10-11).

What changed in 2.5.1

No tool, argument or name changed. Thirty-one calculators that computed something other than their cited reference now compute it, with the same numbers as the website and the REST API (rftools.io changelog, 2026-10-07). Among them: shielding-effectiveness (reflection loss carries η₀, 45.5 dB was missing; multiple reflections added), ground-plane-impedance (µ₀·h·l/w, with a new optional separation input, default 1 mm), speaker-crossover (2nd-order inductors √2·R/ω_c), esd-tvs-diode (IEC 61000-4-2's 3.75 A/kV first peak), common-mode-choke (a 50 Ω/50 Ω system), minimum-conductor-spacing (IPC-2221B Table 6-1 by band), radiated-emission-estimate (CISPR 32 Class B at the distance; no margin below 30 MHz or above 6 GHz) and via-thermal-resistance (IPC-2221 current capacity, new optional tempRise).

What changed in 2.5.0

No tool was added, removed or renamed, and no tool's arguments changed.

• Fourteen new calculators (255 in all), each checked against a cited textbook, standard or datasheet value:
• antennas: helical-antenna, monopole-antenna, antenna-downtilt;
• RF: line-of-sight, wilkinson-power-divider, directional-coupler, circular-waveguide, microstrip-mitered-bend, 5g-nr-band-lookup (3GPP Release 18 band table) and 5g-nr-link-budget;
• power: rc-snubber, rcd-clamp-snubber.
• A new category, `iot` ("IoT & LPWAN"), holding lora-link-budget and ble-link-budget. list_calculators with category: "iot" lists them.
• Corrected outputs:
• filter-designer: its Chebyshev prototype values were wrong from order 4 (g3 1.5733, now 2.3661), a first-order Butterworth gave g1 = 1 (now 2), and the band-pass element values were ten times too small at Q = 10. The values are now computed, not tabulated.
• waveguide-cutoff, free-space-path-loss, rf-link-budget, fresnel-zone, link-margin and radar-range-equation use the exact speed of light, not 3×10⁸. Lengths move by about 0.07 % and path loss by 0.006 dB. radar-range-equation also uses the exact Boltzmann constant.
• planar-spiral-inductor refuses an inner diameter at or above the outer one instead of returning NaN.

What changed in 2.4.0

No existing tool was removed or renamed, and no existing tool's arguments changed: every name and every argument 2.3.0 accepted is accepted the same way.

• New tool: `search_calculators`. Finds calculators by words — "trace impedance on FR4 microstrip" — instead of listing all 255. It matches English titles, keywords, input and output names and descriptions, and the German, Spanish, French, Japanese, Korean and Portuguese titles and keywords, so "マイクロストリップ インピーダンス" finds the microstrip calculator too.
• New tool: `get_calculator_schema`. One calculator's inputs as a JSON Schema (2020-12): each a number with its unit, minimum, maximum, default and description, with the outputs, the formula and its reference, and the page URL. A misspelt identifier is refused with the closest ones.
• `run_calculation` lists what it assumed. A new defaultedInputs field names every declared input the call left out, which therefore took its default. An undeclared input key is still computed around and named in a warning, in the REST API's wording; it is not refused.
• Every tool carries annotations: a title and readOnlyHint, destructiveHint, idempotentHint and openWorldHint, so a host can tell what it may run without asking (see Annotations below).
• Every description says what the tool answers, its inputs' units and ranges (or which tool states t