
Connects Claude to rftools.io's engineering calculator library and simulation pipeline. You get 213 calculators that run locally (microstrip impedance, link budgets, buck converter sizing, filter design) plus 13 server-side simulation tools that require an API key (NEC2 antenna modeling, FDTD, Monte Carlo tolerance analysis, SMPS stability, EMI estimation). Calculators return instant results with units and formulas. Simulations are queued jobs that take 15 to 120 seconds and consume monthly quota. Free tier gets 5 simulation runs per month, paid tiers scale to 10,000. Useful if you're designing RF circuits, power supplies, or PCBs and want validated math without leaving your editor.
MCP server for 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.
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.
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.
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.
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 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
Add to .cursor/mcp.json in your project:
{
"mcpServers": {
"rftools": {
"command": "npx",
"args": ["-y", "rftools-mcp"],
"env": {
"RFTOOLS_API_KEY": "rfc_your_key_here"
}
}
}
}
Add to ~/.codeium/windsurf/mcp_config.json:
{
"mcpServers": {
"rftools": {
"command": "npx",
"args": ["-y", "rftools-mcp"],
"env": {
"RFTOOLS_API_KEY": "rfc_your_key_here"
}
}
}
}
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.
No tool was added, removed or renamed, and no tool's arguments changed.
helical-antenna, monopole-antenna, antenna-downtilt;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;rc-snubber, rcd-clamp-snubber.iot ("IoT & LPWAN"), holding lora-link-budget and
ble-link-budget. list_calculators with category: "iot" lists them.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.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.
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.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.title and readOnlyHint,
destructiveHint, idempotentHint and openWorldHint, so a host can tell
what it may run without asking (see Annotations below).simulate_* descriptions are generated from the website's
tool registry, so they change when the tool does.rftools://reference/{domain}/{id} (see Reference resources below).--manifest: npx rftools-mcp --manifest prints what this build lists —
tools, resources, templates, counts — as JSON, and exits.run_calculation's webUrl is now the page's canonical address, with its
trailing slash.| Tools | read-only | destructive | idempotent | open world |
|---|---|---|---|---|
list_calculators, search_calculators, get_calculator_info, get_calculator_schema, run_calculation, list_simulation_tools, get_simulation_status, get_simulation_result | yes | no | yes | no |
solve_calculation, submit_simulation, run_simulation, every simulate_* | no | no | no | no |
A tool that starts a job or makes a metered call spends the account's monthly allowance, so it is not marked read-only — a host that runs read-only tools without asking would otherwise spend a free account's five runs unprompted — and it is not idempotent, because a repeat spends again (identical job submissions merge only inside 60 seconds). Nothing deletes or overwrites anything, and every tool talks only to rftools.io, so no tool is destructive or open-world.
solve_calculation. Finds the value of one calculator input
that makes an output equal a target — the trace width for 50 Ω, the gap for
90 Ω — instead of an agent guessing values and calling run_calculation in a
loop. Unlike every other calculator tool, this runs the search server-side
on rftools.io and requires an API key and spends one metered call — see
solve_calculation below.run_calculation returns a
provenance object beside the values: the method (calculator:<slug>), the
engine (mcp@<version>), the published formula source, the calculator's stated
assumptions, the inputs it computed from, whether they lie inside the range
the calculator is stated for (and, for a fitted model, its validated range
and worst-case error), when it was computed and how long it took. It is the
same object the rftools.io API returns.warnings, and so is an input outside its stated range —
the value is still computed.provenance is returned whole in the default
summary. Series are still described rather than listed.simulate_<jobType> tool (e.g. simulate_impedance_matching) with a
real input schema — name, type, unit, range, options and default per
parameter — generated from the job type's parameter contract. run_simulation
still exists as a compatibility form that takes jobType and params, but
prefer the typed tool: it is the one an agent can read the schema of.inputFiles: [{name, content}])
or by path on this machine (inputPaths); a file-input job type needs
RFTOOLS_API_KEY — see Files below.submit_simulation / get_simulation_status / get_simulation_result
are the fire-and-forget primitives underneath run_simulation and the typed
tools, for a caller that wants to submit, do other work, and poll later.run_simulation is now bounded by waitSeconds (default 90, maximum
600): it submits, polls, and if the job has not finished by the bound it
returns the job id, status, progress and stage rather than blocking further
— the job keeps running, and a later get_simulation_status /
get_simulation_result call picks it up.summary, warnings, provenance,
every scalar value, and long series described by length and extremes rather
than listed in full. Pass full: true for the whole payload.simulate_* call sends only the parameters
you name; it no longer fills in the contract's defaults itself. Since a
sampling job type's random seed is derived from the request body, omitting a
parameter and sending it at its default are the same request to the solver
but not the same body, and can draw a different sample. Set randomSeed to
pin a run exactly.errorKind, not
by matching message text — see When something goes wrong below.Breaking:
list_simulation_tools no longer carries a hand-written sentence describing
each job type's parameters; it lists them as a plain array of names
(params: string[]). Read a simulate_* tool's own input schema for the
type, unit, range, options and default of each parameter.list_calculators, search_calculators, get_calculator_info,
get_calculator_schema and run_calculation need no API key — they run
locally, for free. solve_calculation is the exception: it runs on rftools.io
itself and needs a key, exactly as run_calculation needs none — see its own
section below.
list_calculatorsList available calculators, optionally filtered by category.
"List all RF calculators"
"What antenna calculators are available?"
"Show me power electronics calculators"
Parameters:
category (optional): rf, pcb, power, signal, antenna, general, motor, protocol, emc, thermal, sensor, unit-conversion, audio, iotsearch_calculatorsFind calculators by words, in English or in any of the site's other six languages, ranked by how well they match.
"Which calculator gives trace impedance on FR4 microstrip?"
"Find a calculator for battery charge time"
Parameters:
query (required): the words to matchcategory (optional): restrict to one category; an unknown one is refused with the listlimit (optional): 1 to 25 results, default 10Each result carries slug, title, category, a one-line description, the
page url and its score; matched says how many calculators matched in all.
A search that matches nothing is returned as an error saying so, not as an
empty list.
The ranking is deterministic, so the hosted endpoint can reproduce it exactly:
text is NFKC-normalised and lower-cased; Latin text splits into words (accents
folded, one plural s dropped), Japanese and Korean into character bigrams;
each calculator field has a weight (English title 10, translated title 8,
keywords 6, translated keywords 5, input and output names 3, description 2);
a calculator scores the sum over the query's words of its best field weight
times ln(1 + N/df); ties keep registry order. The rules are written out in
src/calculator-search.ts.
get_calculator_infoGet detailed info about a calculator — inputs with units/defaults, outputs, and the formula used.
"What inputs does the microstrip impedance calculator need?"
"Show me the buck converter calculator parameters"
Parameters:
slug (required): Calculator identifier (e.g. "microstrip-impedance")Each input carries its stated min/max (the same bounds run_calculation's
provenance.validRange checks against). An input with neither is unbounded —
solve_calculation needs an explicit range to solve for one of those.
get_calculator_schemaThe same inputs as a JSON Schema (draft 2020-12) — what a call to
run_calculation may send — with the outputs, the formula and the page URL.
Parameters:
slug (required): Calculator identifier. A misspelt one is refused, naming the three closest (microstrip-impedence → microstrip-impedance, …).Returns inputSchema (each property a number with title, description
— label, unit and tooltip — default, minimum, maximum and x-unit),
outputs (key, label, unit), formula (primary, latex where there
is one, and reference, the source the formula comes from) and url.
run_calculationRun a calculator with specific inputs. Returns results with units, a link to the interactive version on rftools.io, defaultedInputs, and the result's provenance (formula source, assumptions, inputs used, whether they lie inside the calculator's stated range, engine version and time). An input left out takes its default and is named in defaultedInputs; an input key the calculator does not declare is not read and is named in warnings; a value outside the stated range is computed and named in warnings. Runs locally — instant, no quota consumed.
"Calculate microstrip impedance for a 0.3mm trace on 0.2mm Rogers RO4003C"
"What's the link budget for a 2.4 GHz link over 500m?"
"Size a buck converter: 12V in, 3.3V out, 2A"
Parameters:
slug (required): Calculator identifierinputs (required): Object with input values, e.g. {"traceWidth": 0.3, "substrateHeight": 0.2}solve_calculation — needs an API key, spends one metered callFind the value of one calculator input that makes an output equal a target,
instead of calling run_calculation in a loop to search for it yourself. The
search runs server-side on rftools.io's own calculators — the same engine
/calculate uses — so it needs an API key (RFTOOLS_API_KEY), the same one
/calculate itself requires, and it is metered like any other API call.
reached: false means no value inside the search range reaches the target;
the value returned is then the nearest one the search found, not a guess.
"What trace width gives 50 Ω on 1.6mm FR4 with 1oz copper?"
"Find the gap that gives 90 Ω differential impedance for a 0.15mm trace"
Parameters:
slug (required): Calculator identifierinputs (required): The calculator's other inputs, keyed by name — not including solveFor's own inputsolveFor (required): Which declared numeric input to solve for, e.g. "traceWidth"target (required): {"output": "impedance", "value": 50} — the output key and the value it should reachgrid (optional): Round the solution to the nearest multiple of this manufacturing grid, e.g. 0.001 (mm)range (optional): [low, high], narrowing the search inside solveFor's stated bound. Required when get_calculator_info shows no min/max for that input.The response carries value (on the grid, if one was given), unrounded,
reached, evaluations, the solve's own warnings (e.g. another crossing
exists in range), and result — exactly what run_calculation//calculate
return for the calculator at that value, provenance included.
Server-side jobs that are too heavy for in-browser computation. Each of the 13 job types is its own tool, simulate_<name>, whose input schema is generated from that job type's parameter contract: every parameter typed, with its unit, range, options, default and any free-lane bound stated. A call is checked against that contract before anything is sent, so a wrong parameter name comes back naming the key and the keys that are accepted, and spends no quota.
Quota: Free: 5 runs/month · Pro: 100/month · API tier: 10,000/month. Without a key a job that takes no file still runs, on the free lane, and the response says which limits applied. A job that takes a file needs a key — see Files below.
Waiting: a simulate_* call submits and waits up to waitSeconds (default 90, maximum 600), polling immediately — a mode that finishes in a second costs no delay — and reporting progress to hosts that ask for it. On reaching the bound it returns the job id, status, progress and stage; the job keeps running, and get_simulation_status and get_simulation_result pick it up. waitSeconds: 0 submits and returns at once.
Results: the default is a summary — the result's summary, warnings and provenance, every scalar value, and links — with series longer than 50 points described by their length and extremes rather than listed, so a 100 kB result arrives as about 6 kB. Pass full: true for the whole payload. The link to the stored result (resultUrl) is presigned and lives 15 minutes; ask for the status again to mint a fresh one.
Repeat submissions: an identical submission inside 60 seconds returns the job already running rather than starting a second one.
Files: a file-input job type takes either inputFiles: [{name, content}] (inline text, up to 5 MB in one call) or inputPaths: ["/path/to/file.s2p"] (read from this machine). The server obtains the presigned upload, sends the file, and submits the job with the resulting key.
Uploading a file needs an API key; set RFTOOLS_API_KEY. The service refuses an anonymous upload, so this server refuses it first — locally, before the file is read and before any request is made — and says which variable to set rather than passing back a bare 401. The uploaded object is recorded against the key's account, and only that account may submit it.
| Tool | jobType | What it does | Files | Time budget | Paid-only / free-lane bound |
|---|---|---|---|---|---|
simulate_antenna_sim | antenna_sim | Wire Antenna Simulator (NEC-2) | — | 1200 s | solveMode: optimize |
simulate_emi_radiated | emi_radiated | EMI Radiated Emissions Estimator | — | 240 s | — |
simulate_eye_diagram | eye_diagram | Eye Diagram from S-Parameters | 1 × .s2p .s4p | 120 s | — |
simulate_fdtd_sparam | fdtd_sparam | FDTD Transmission Line Simulator | — | 32400 s | solveMode: normal, fine |
simulate_filter_monte_carlo | filter_monte_carlo | RF Filter Monte Carlo Analysis | — | 120 s | monteCarloIterations ≤ 500 |
simulate_impedance_matching | impedance_match | Broadband Impedance Matching Synthesizer | 0–2 × .s2p | 120 s | — |
simulate_magnetics_optimizer | magnetics_optimizer | Magnetics & Transformer Design Optimizer | — | 360 s | — |
simulate_pdn_impedance | pdn_impedance | PDN Impedance Analyzer & Decoupling Capacitor Optimizer | — | 360 s | — |
simulate_radar_detection | radar_detection | Radar Detection Performance Monte Carlo | — | 300 s | — |
simulate_rf_cascade | rf_cascade | RF Cascade Budget Analyzer | 0–12 × .s2p | 180 s | — |
simulate_sat_link_budget | sat_link_budget | Satellite & Terrestrial Link Budget | — | 240 s | — |
simulate_smps_control_loop | smps_control_loop | SMPS Control Loop Stability Analyzer | — | 300 s | — |
simulate_sparam_pipeline | sparam_pipeline | S-Parameter Analysis Pipeline | 1–4 × .s1p–.s4p | 120 s | — |
The time budget is the lane's cap, not an estimate: most jobs finish in 15–120 seconds, and queue wait may add more.
list_simulation_toolsEvery job type with its tool name, parameter names, file rules, time budget and free-lane bounds — all read from the same contract the tools are generated from.
submit_simulationSubmit by job type and return at once with the job id, queue position and time budget. Takes jobType, params, and inputFiles / inputPaths for file-input job types — which need an API key; set RFTOOLS_API_KEY.
get_simulation_statusProgress, stage, queue position, start and finish times for a job id.
get_simulation_resultThe finished result for a job id, summarised by default, whole with full: true.
run_simulationThe compatibility form of a simulate_* call: jobType, params, optional files (which need a key, as above), waitSeconds (default 90, max 600) and full. Prefer the typed simulate_* tool for the job you want — it is the one whose schema an agent can read.
"Analyse the PDN of a 100 × 80 mm four-layer board, port at the IC, target 10 mΩ"
"Run an eye diagram on this .s4p at 10 Gbps with PRBS-15"
"Synthesize a broadband matching network from 50Ω to 200Ω between 800–1200 MHz"
"Simulate a 3-element Yagi at 144 MHz and give me the pattern"
"Estimate radiated emissions from a 10 cm trace carrying 50 mA at 100 MHz"
Failures are classified by HTTP status and by the service's own error kind, never by matching text: an invalid key, a spent allowance, a rate limit with its retry time, a refused parameter (with the service's own detail, unchanged), a job too large for its lane, a mode the tier does not carry, a timeout and a service fault each read differently. Polling stops at once on a 4xx, and after five failures in a row that are not.
The tables published under rftools.io/reference are MCP resources, one per page, built from the same data the pages are, so the counts always match the site. Each domain has a template for lookup by identifier:
| Template | What each entry holds |
|---|---|
rftools://reference/bands/{id} | A frequency band: limits in Hz, wavelength, ITU designation, uses, propagation and regulatory notes |
rftools://reference/connectors/{id} | An RF connector: impedance, frequency and power limits, VSWR, mating cycles, materials, uses |
rftools://reference/values/{id} | A standard-value table: E24/E96 resistors, capacitors, AWG, drills, threads, SI prefixes |
rftools://reference/codes/{id} | A marking-code chart: SMD resistor codes, capacitor value, voltage, tolerance and dielectric codes |
rftools://reference/pcb/{id} | A PCB table: copper weight against thickness and current, standard board thicknesses |
A read returns JSON with the entry's values, its source (the standards the
page names and its note on where the values come from) and the page url. An
unknown identifier fails with invalid params, naming the template and the
valid identifiers. Hosts that offer completion can complete {id}.
You: I need a 50-ohm microstrip on 1.6mm FR4 with 1oz copper. What trace width?
AI: Calls
run_calculationwith microstrip-impedance → A trace width of ~2.9mm gives you 50.2 Ω on 1.6mm FR4 (εr=4.2). View on rftools.io →
You: Will my 100mW 915 MHz LoRa link work at 2km with 3dBi antennas?
AI: Calls
run_calculationwith rf-link-budget → Received power: -72 dBm. With LoRa sensitivity at -137 dBm, you have 65 dB of link margin. Easily workable. View on rftools.io →
You: Design a buck converter: 24V input, 5V output, 3A load, 500kHz switching.
AI: Calls
run_calculationwith buck-converter → Duty cycle: 20.8%, inductor: 17.4 μH, output cap: 22 μF. View on rftools.io →
| Category | Count | Examples |
|---|---|---|
| RF & Microwave | 36 | Microstrip impedance, coplanar waveguide (CPW/GCPW), VSWR/return loss, Smith chart, link budget, noise figure cascade, radar range, free-space path loss, mixer spur, Wilkinson divider, directional coupler, circular waveguide, line of sight, 5G NR band lookup and link budget |
| PCB Design | 36 | Trace width for current, controlled impedance, edge-coupled stripline pairs (symmetric, offset, embedded), differential via with stub loss, skin depth percentage, conductor-to-pad width, BGA breakout width, aperture diagonal, maximum pad diameter, effective dielectric constant, via step response, microvia current capacity, asymmetric (offset) stripline, dual stripline, broadside-coupled pair, differential pair, via calculator, crosstalk, critical trace length, fusing current, decoupling capacitor, padstack/annular ring, BGA land pad, conductor spacing, planar spiral inductor, embedded resistor, via voltage drop |
| Power Electronics | 23 | Buck converter, boost converter, flyback, LDO thermal, battery life, MOSFET dissipation, solar panel sizing, RC snubber, RCD clamp snubber |
| Signal Processing | 14 | Filter designer, ADC SNR, FFT bin resolution, PLL loop filter, BER/SNR, Johnson noise, rise time to bandwidth |
| Antenna Design | 11 | Dipole, patch, Yagi-Uda, horn, parabolic dish, loop, EIRP, beamwidth, helical, monopole/whip, antenna downtilt |
| General Electronics | 24 | Ohm's law, crystal PPM tolerance, op-amp gain, 555 timer, BJT bias, MOSFET operating point, Schmitt trigger, crystal load capacitance |
| Motor Control | 22 | DC motor speed, stepper, BLDC, servo, PID tuning, gear ratio, H-bridge selection, torque converter |
| Communications | 11 | UART baud rate, I2C pull-up, SPI timing, CAN bus, USB termination, RS-485, Ethernet, Modbus, LIN bus |
| EMC/EMI | 16 | Shielding effectiveness, EMI filter, ferrite bead, ESD/TVS diode, radiated emission estimate, common-mode choke |
| Thermal | 6 | Heatsink calculator, junction temperature, thermal via array, PCB trace temperature |
| Sensor Interface | 17 | NTC thermistor, RTD, thermocouple, Wheatstone bridge, load cell, photodiode, 4-20 mA loop transmitter |
| Unit Conversion | 19 | dBm↔Watts, rectangular↔polar, frequency↔wavelength, length (mm/mil/inch), AWG wire, capacitor code, temperature, inductance, data rate |
| Audio Electronics | 18 | Speaker crossover, room modes, headphone power, class-D efficiency, audio transformer, equalizer Q |
| IoT & LPWAN | 2 | LoRa link budget (sensitivity by spreading factor, time on air, duty-cycle off-time, Okumura–Hata range), BLE link budget by PHY (ITU-R P.1238 indoor path loss) |
LLMs are unreliable at arithmetic. They may:
This MCP server calls the exact same validated calculator code that runs on rftools.io. Hammerstad-Jensen for microstrip, Friis for path loss, exact dB/linear conversions — real engineering formulas, not LLM approximations.
Calculators are bundled as pure TypeScript functions — no API calls, no network latency, no rate limits. The AI calls the function directly and gets instant results.
AI Agent ←stdio→ rftools-mcp ←direct call→ calculator function
solve_calculation is the one calculator tool that is not a direct call:
it runs the search on rftools.io's own calculators, so it needs an API key
and is metered like a plain /calculate call — no queue, no polling, one
request and one response.
AI Agent ←stdio→ rftools-mcp ←HTTPS (key required)→ POST /calculate/solve
Simulation tools run server-side on rftools.io infrastructure (AWS Lambda + SQS + EC2/Fargate workers). Their input schemas are generated at build time from the same parameter contract the website's forms are built from, so a contract change reaches the agent at the next release rather than through a hand-edited string. The server validates the call, uploads any files, submits the job, polls it within the wait bound while reporting progress, and returns a summarised result with a link to the whole payload.
AI Agent ←stdio→ rftools-mcp ←HTTPS (key optional)→ rftools.io API → SQS → worker
←poll /v1/jobs/{id}←
←result JSON from a 15-minute presigned link←
npx rftools-mcp --manifest — Everything this build lists (tools with their descriptions, annotations and input schemas, resources, templates and counts) as one JSON document; the agents page is built from itMIT