# AC Resonance & Reactance API > AC reactance and LC/RC tuning maths as an API, computed locally and deterministically. The reactance endpoint computes the capacitive reactance Xc = 1/(2πfC) and the inductive reactance Xl = 2πfL at a given frequency, and — when both a capacitor and an inductor are supplied — the net series reactance X = Xl − Xc, whether the circuit looks inductive, capacitive or resonant, and the impedance magnitude. The resonant endpoint computes the LC resonant frequency f₀ = 1/(2π√(LC)), or, given a target frequency and one component, solves the other component you need to tune to it. The cutoff endpoint computes the RC or RL filter cutoff frequency — fc = 1/(2πRC) for RC, fc = R/(2πL) for RL — and the time constant. Frequencies are in hertz; capacitance, inductance and resistance accept SI base units with handy µF/nF/pF and mH/µH inputs. Everything is computed locally and deterministically, so it is instant and private. Ideal for electronics, RF, audio-filter and embedded app developers, tuning and filter-design tools, and electronics education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is AC reactance & LC/RC tuning; for LED series-resistor sizing use an LED-resistor API and for VSWR and impedance match use a VSWR API. ## Authentication All requests require your oanor API key in the `x-oanor-key` header. Get one at https://www.oanor.com/developer/keys. ```bash curl -H "x-oanor-key: oanor_live_…" "https://api.oanor.com/resonance-api/..." ``` ## Pricing - **Free** (Free) — 2,000 calls/Mo, 2 req/s - **Starter** ($8/Mo) — 25,000 calls/Mo, 5 req/s - **Pro** ($22/Mo) — 150,000 calls/Mo, 15 req/s - **Mega** ($69/Mo) — 790,000 calls/Mo, 40 req/s ## Endpoints ### Resonance #### `GET /v1/cutoff` — RC/RL filter cutoff **Parameters:** - `resistance` (query, required, string) — Resistance (Ω) Example: `1000` - `capacitance_uf` (query, optional, string) — Capacitance (µF) for an RC filter Example: `1` - `inductance_mh` (query, optional, string) — Or inductance (mH) for an RL filter **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/resonance-api/v1/cutoff?resistance=1000&capacitance_uf=1" ``` **Response:** ```json { "data": { "note": "RC filter: fc = 1/(2πRC), τ = RC. Same fc for low-pass and high-pass.", "inputs": { "capacitance_f": 1.0e-6, "resistance_ohm": 1000 }, "filter_type": "RC", "time_constant_s": 0.001, "cutoff_frequency_hz": 159.154943 }, "meta": { "timestamp": "2026-06-04T18:38:10.322Z", "request_id": "c72aee63-d8b8-4b0b-ab49-0ed8546a369e" }, "status": "ok", "message": "Filter cutoff", "success": true } ``` #### `GET /v1/reactance` — Reactance at a frequency **Parameters:** - `frequency` (query, required, string) — Frequency (Hz) Example: `1000` - `capacitance_uf` (query, optional, string) — Capacitance (µF) Example: `1` - `inductance_mh` (query, optional, string) — Inductance (mH) Example: `10` - `capacitance` (query, optional, string) — Or capacitance (F) - `inductance` (query, optional, string) — Or inductance (H) **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/resonance-api/v1/reactance?frequency=1000&capacitance_uf=1&inductance_mh=10" ``` **Response:** ```json { "data": { "note": "Xc = 1/(2πfC), Xl = 2πfL. Net series reactance X = Xl − Xc; |Z| ignores resistance.", "inputs": { "frequency_hz": 1000, "inductance_h": 0.01, "capacitance_f": 1.0e-6 }, "reactance_type": "capacitive", "net_reactance_ohm": -96.32309, "impedance_magnitude_ohm": 96.32309, "inductive_reactance_ohm": 62.831853, "capacitive_reactance_ohm": 159.154943 }, "meta": { "timestamp": "2026-06-04T18:38:10.421Z", "request_id": "bf3a47b8-cce7-46db-8b80-47c6eb2d9610" }, "status": "ok", "message": "Reactance", "success": true } ``` #### `GET /v1/resonant` — LC resonant frequency **Parameters:** - `inductance_mh` (query, optional, string) — Inductance (mH) Example: `10` - `capacitance_uf` (query, optional, string) — Capacitance (µF) Example: `1` - `frequency` (query, optional, string) — Target frequency (Hz) to solve a component **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/resonance-api/v1/resonant?inductance_mh=10&capacitance_uf=1" ``` **Response:** ```json { "data": { "note": "f₀ = 1/(2π√(LC)). At resonance the inductive and capacitive reactances cancel.", "inputs": { "inductance_h": 0.01, "capacitance_f": 1.0e-6 }, "resonant_frequency_hz": 1591.549431, "resonant_frequency_khz": 1.591549, "resonant_frequency_mhz": 0.001591549 }, "meta": { "timestamp": "2026-06-04T18:38:10.546Z", "request_id": "840be71d-c87c-499d-b86b-87d147e3478a" }, "status": "ok", "message": "LC resonance", "success": true } ``` ### Meta #### `GET /v1/meta` — Spec **Example:** ```bash curl -H "x-oanor-key: $KEY" \ "https://api.oanor.com/resonance-api/v1/meta" ``` **Response:** ```json { "data": { "notes": "Base SI units: frequency Hz, capacitance F, inductance H, resistance Ω. Convenience inputs accepted: capacitance_uf/_nf/_pf, inductance_mh/_uh.", "service": "resonance-api", "formulae": { "rc_cutoff": "fc = 1/(2πRC), τ = RC", "rl_cutoff": "fc = R/(2πL), τ = L/R", "lc_resonance": "f₀ = 1/(2π√(LC))", "inductive_reactance": "Xl = 2πfL", "capacitive_reactance": "Xc = 1/(2πfC)" }, "endpoints": { "GET /v1/meta": "This document.", "GET /v1/cutoff": "RC or RL filter cutoff frequency and time constant.", "GET /v1/resonant": "LC resonant frequency, or solve C or L for a target frequency.", "GET /v1/reactance": "Capacitive/inductive reactance at a frequency and net series reactance." }, "description": "AC reactance and LC/RC tuning calculator: capacitive and inductive reactance at a frequency, LC resonant frequency (or solve the missing component), and RC/RL filter cutoff frequency and time constant." }, "meta": { "timestamp": "2026-06-04T18:38:10.659Z", "request_id": "c3c9c9fc-523a-47eb-88ee-820d659fd4a0" }, "status": "ok", "message": "Meta", "success": true } ``` --- Marketplace page: https://www.oanor.com/api/resonance-api OpenAPI spec: https://www.oanor.com/api/resonance-api/openapi.json