rftools-mcp
[npm version]
[License: MIT]
[MCP]
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.
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):
Omit the env block to use calculators only. Restart Claude Desktop after saving.
Claude Code
To add your API key:
Cursor
Add to .cursor/mcp.json in your project:
Windsurf
Add to ~/.codeium/windsurf/mcp_config.json:
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 them), one complete example call and what it
returns. The 13
simulate_* descriptions are generated from the website's
tool registry, so they change when the tool does.
- Reference tables as resources: frequency bands, RF connectors, standard
values, component marking codes and PCB specifications, at
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.
Annotations
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.
What changed in 2.2.0
- New tool:
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.
What changed in 2.1.0
- Calculator results carry provenance.
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.
- An input left out takes its default, as on the website and the API; it
used to reach the calculator as undefined. An input the calculator does not
read is named in
warnings, and so is an input outside its stated range —
the value is still computed.
- A simulation result's
provenance is returned whole in the default
summary. Series are still described rather than listed.
What changed in 2.0.0
- One typed tool per job type. Each of the 13 simulation job types now has
its own
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.
- Uploads go through this server, inline (
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.- Results are summarised by default —
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.
- No defaults are posted. A
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.
- Typed errors. Failures are classified by the service's
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.- Unknown parameter keys are now refused locally, before any request leaves
this machine — the same contract the service validates against, checked
here first.
Calculator tools
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_calculators
List available calculators, optionally filtered by category.
Parameters:
category (optional): rf, pcb, power, signal, antenna, general, motor, protocol, emc, thermal, sensor, unit-conversion, audio, iot
search_calculators
Find calculators by words, in English or in any of the site's other six
languages, ranked by how well they match.
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 10
Each 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_info
Get detailed info about a calculator — inputs with units/defaults, outputs, and the formula used.
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_schema
The 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_calculation
Run 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.
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 call
Find 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.
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.
Simulation tools — no API key required unless the job takes a file
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.
The 13 job types
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_tools
Every 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_simulation
Submit 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_status
Progress, stage, queue position, start and finish times for a job id.
get_simulation_result
The finished result for a job id, summarised by default, whole with full: true.
run_simulation
The 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.
When something goes wrong
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.
Reference resources
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:
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}.
Example Conversations
PCB Design
You: I need a 50-ohm microstrip on 1.6mm FR4 with 1oz copper. What trace width?
AI: Calls run_calculation with microstrip-impedance → A trace width of ~2.9mm gives you 50.2 Ω on 1.6mm FR4 (εr=4.2). View on rftools.io →
RF Link Budget
You: Will my 100mW 915 MHz LoRa link work at 2km with 3dBi antennas?
AI: Calls run_calculation with 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 →
Power Electronics
You: Design a buck converter: 24V input, 5V output, 3A load, 500kHz switching.
AI: Calls run_calculation with buck-converter → Duty cycle: 20.8%, inductor: 17.4 μH, output cap: 22 μF. View on rftools.io →
All 255 Calculators
Why Use This Instead of Asking the AI to Calculate?
LLMs are unreliable at arithmetic. They may:
- Use simplified formulas that omit corrections (e.g. copper thickness in microstrip)
- Confuse units (mils vs mm, dBm vs dBW)
- Accumulate rounding errors
- Confidently present wrong answers
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.
How It Works
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.
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.
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.
Machine-Readable Documentation
- rftools.io/agents — This server's tools, install steps and example prompts, in seven languages
- rftools.io/llms.txt — Summary with API info and MCP setup
- rftools.io/llms-full.txt — Complete listing of all 255 calculators with inputs, outputs, units, and URLs
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 it
Links
License
MIT
