rftools-mcp

MCP server for rftools.io — 241 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.

Related MCP server: mcp-engineering-tools

Setup

Without API key

All 241 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 2.4.0

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 241. 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.

"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

search_calculators

Find 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 match

• category (optional): restrict to one category; an unknown one is refused with the list

• limit (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.

"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_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.

"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 identifier

• inputs (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.

"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 identifier

• inputs (required): The calculator's other inputs, keyed by name — not including solveFor's own input

• solveFor (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 reach

• grid (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.

"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"

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 241 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.

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←

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 241 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

• Website: rftools.io

• npm: npmjs.com/package/rftools-mcp

• Blog: rftools.io/blog

• Announcement: rftools.io Now Speaks MCP

License

MIT