# calc.engineer
> Engineering calculator network — RF, LoRa/Meshtastic, homelab, solar/power, PCB.
> All tools available via MCP, REST API, or interactive web UI.

## How to Use (3 ways)

### 1. REST API — free, no signup
The happy path: get a key → call tools → parse structured JSON.

```bash
# Step 1: Get a free API key (no signup required)
curl -X POST https://calc.engineer/api/keys
# → {"key":"ce_abc123...","rate_limit":"5,000/day","expires_in":"24h"}

# Step 2: Discover tools
curl https://calc.engineer/api                    # Full catalog
curl https://calc.engineer/api/link_budget        # Single tool schema

# Step 3: Compute
curl -X POST https://calc.engineer/api/link_budget \
  -H "Content-Type: application/json" \
  -H "X-Api-Key: ce_abc123..." \
  -d '{"freq_mhz": 915, "tx_dbm": 20, "dist_km": 5}'
# → {"result":{...},"tool":"link_budget","chain":{"feeds":[...],"accepts_from":[...]}}
```

### 2. MCP — for AI agents (paid)
All 88 tools as native function calls with typed schemas. Requires a paid API key.

```bash
# Claude Code (pass your paid key via query param)
claude mcp add calc-engineer --transport http "https://calc.engineer/mcp?key=YOUR_PAID_KEY"
```
```json
// Cursor / Windsurf / VS Code
{ "mcpServers": { "calc-engineer": { "url": "https://calc.engineer/mcp?key=YOUR_PAID_KEY" } } }
```

### 3. Web UI — for humans
Visit https://calc.engineer and browse tools by category. Visual, guided inputs — not just text boxes.

### Authentication & Rate Limits
| Surface | Rate Limit | Auth |
|---------|-----------|------|
| REST (no key) | 200/day per IP | None |
| REST (free key) | 5,000/day per key | `POST /api/keys` (no signup) |
| REST (paid key) | Unlimited (metered) | `POST /api/keys` with JWT |
| MCP | Unlimited (metered) | Paid API key required (`?key=` or `X-Api-Key`) |
| Web UI | No limit | None |

## Categories (88 tools)
- rf — Link budgets, FSPL, dipole, microstrip, noise figure, VSWR, attenuators, SPICE simulation
- mesh — LoRa airtime, SNR margin, channel utilization, range estimation, Meshtastic power/range
- homelab — ZFS capacity/RAM, TCP throughput, WireGuard MTU, subnets, RAID IOPS, rack capacity
- power — Battery life, wire gauge, solar sizing, UPS runtime, solar ROI, string sizing
- pcb — Voltage divider, RC/LC filters, impedance match, trace width, 555 timer, op-amp gain
- general — Unit conversion, loan amortization, compound interest, percentages, statistics, geometry

## Tool Chains
fspl -> link_budget (path loss feeds full link analysis)
noise_figure_cascade.total_nf_db -> link_budget (NF-aware budget)
link_budget.rx_power_dbm -> snr_margin.rx_dbm (receive chain analysis)
solar_load_audit.total_daily_kwh -> solar_sizing (size system from appliance audit)
solar_sizing.battery_kwh -> battery_autonomy (days of backup from system size)
ohms_law -> led_resistor -> trace_width (component to PCB layout chain)
resistor_color_code -> op_amp_gain (decode resistor then calculate gain)
voltage_divider -> rc_filter (bias network to filter design)

## All Tools

- **fspl** — Calculate free-space path loss from frequency and distance.
- **link_budget** — Compute a full RF link budget with EIRP, path loss, and link margin.
- **dipole** — Calculate dipole or quarter-wave antenna length for a given frequency.
- **microstrip** — Calculate microstrip trace width for a target characteristic impedance.
- **dbm_convert** — Convert dBm to milliwatts, watts, dBW, and RMS voltage.
- **noise_figure_cascade** — Calculate cascaded noise figure of a multi-stage receiver chain.
- **vswr** — Convert between VSWR, return loss, and reflection coefficient.
- **attenuator_pi** — Design a Pi-topology resistive attenuator pad for a target attenuation.
- **attenuator_tee** — Design a Tee-topology resistive attenuator pad for a target attenuation.
- **fresnel_zone** — Calculate Fresnel zone radius and 60% clearance for a radio link.
- **wavelength_freq** — Convert between RF frequency and wavelength in multiple units.
- **spice_template** — Generate SPICE netlists from parameterized circuit templates.
- **spice_simulate** — Run SPICE circuit simulations with automatic scaling from WASM to container.
- **lora_airtime** — Calculate LoRa packet time-on-air and duty cycle interval.
- **snr_margin** — Check LoRa link SNR margin against the demodulation threshold.
- **channel_utilization** — Estimate mesh channel utilization and max node count before congestion.
- **lora_range_estimate** — Estimate LoRa maximum range with terrain correction from link budget.
- **lora_sensitivity** — Calculate LoRa receiver sensitivity from SF, bandwidth, and noise figure.
- **duty_cycle_budget** — Calculate LoRa duty cycle budget and max messages per hour by region.
- **meshtastic_range** — Estimate Meshtastic range using real device profiles and channel presets.
- **eirp_compliance** — Check EIRP compliance against regional regulatory limits for LoRa.
- **meshtastic_power** — Estimate Meshtastic node battery life from device, role, and settings.
- **lora_param_optimizer** — Recommend optimal LoRa SF, bandwidth, and TX power for your target range.
- **zfs_capacity** — Calculate usable ZFS pool capacity for any RAID level and disk config.
- **zfs_ram** — Calculate recommended RAM and ARC sizing for a ZFS pool.
- **tcp_throughput** — Calculate max TCP throughput from bandwidth, latency, and window size.
- **wireguard_mtu** — Calculate the optimal WireGuard tunnel MTU with overhead breakdown.
- **subnet_calculator** — Calculate IPv4 subnet details from CIDR notation.
- **raid_iops** — Estimate RAID array IOPS and latency for a given disk and RAID config.
- **power_cost** — Calculate homelab power consumption, electricity cost, and circuit load.
- **cooling_btu** — Estimate cooling load in BTU/hr for a homelab or server closet.
- **rack_capacity** — Calculate rack space, weight, and PDU requirements for your gear.
- **network_bandwidth** — Plan network link capacity and identify bandwidth bottlenecks.
- **thermal_enclosure** — CFD thermal simulation of rectangular enclosures for cooling analysis.
- **heatsink_cfd** — CFD simulation of fin-array heatsinks for thermal resistance and pressure drop.
- **pcb_thermal** — PCB thermal simulation with per-component junction temperature analysis.
- **battery_life** — Estimate battery runtime and energy from capacity, voltage, and current.
- **wire_gauge** — Find the minimum AWG wire gauge for a given current and voltage drop.
- **solar_sizing** — Size an off-grid solar system: panels, batteries, and charge controller.
- **ups_runtime** — Estimate UPS backup runtime from battery specs and connected load.
- **mah_to_wh** — Convert battery capacity from mAh to watt-hours, kWh, and joules.
- **watts_to_amps** — Convert watts to amps and milliamps for a given voltage.
- **voltage_drop** — Calculate voltage drop across a wire run for a given gauge and current.
- **battery_charge_time** — Estimate battery charge time from capacity, current, and efficiency.
- **solar_load_audit** — Calculate total daily energy usage from an appliance list for solar sizing.
- **solar_roi** — Calculate solar system ROI, payback period, and levelized cost of energy.
- **battery_autonomy** — Calculate how many days a battery bank can sustain loads without solar.
- **string_sizing** — Calculate optimal solar panel string and MPPT configuration.
- **generator_offset** — Compare total cost of generator vs. solar+battery over time.
- **wire_ampacity** — NEC 310.16 ampacity lookup with temperature and conductor count derating.
- **inverter_sizing** — Size a DC-to-AC inverter from load requirements with surge and derating.
- **voltage_divider** — Calculate voltage divider output, current, and power dissipation.
- **rc_filter** — Compute RC filter cutoff frequency, time constant, and phase shift.
- **lc_resonance** — Calculate LC circuit resonant frequency, Q factor, and bandwidth.
- **impedance_match** — Design an L-network impedance matching circuit between two impedances.
- **trace_width** — Calculate minimum PCB trace width for a given current (IPC-2221).
- **ohms_law** — Solve Ohm's Law: provide any 2 of V, I, R, P to get all 4.
- **resistor_color_code** — Decode 4-band or 5-band resistor color codes to resistance and tolerance.
- **led_resistor** — Calculate the current-limiting resistor for driving LEDs.
- **timer_555** — Calculate 555 timer IC timing for astable and monostable modes.
- **op_amp_gain** — Calculate op-amp voltage gain for inverting, non-inverting, and differential circuits.
- **capacitor_charge** — Calculate RC capacitor charge time, energy stored, and transient voltages.
- **pcb_via_current** — Calculate PCB via current capacity and barrel resistance (IPC-2221).
- **power_supply_decoupling** — Select bypass and bulk decoupling capacitors for IC power supply pins.
- **log_calc** — Compute logarithms of a positive number in any base.
- **sig_figs** — Count significant figures in a number and optionally round to N significant figures.
- **scientific_notation** — Convert any number to scientific notation and engineering notation.
- **percentage_calc** — Calculate what percentage one number is of another.
- **percentage_increase** — Calculate the percentage change between an old value and a new value.
- **exponent_calc** — Compute the result of raising a base to an exponent (base^exponent).
- **square_root** — Compute the square root of a non-negative number.
- **circumference** — Calculate the circumference and area of a circle given either a radius or diameter.
- **slope_calc** — Calculate the slope, y-intercept, line equation, angle, and distance between two points in a 2D Cartesian plane.
- **pythagorean_theorem** — Solve for any side of a right triangle using the Pythagorean theorem (a² + b² = c²).
- **p_value** — Calculate the p-value for a z-score or t-statistic.
- **confidence_interval** — Calculate the confidence interval for a sample mean.
- **sales_tax** — Calculates total cost including sales tax for a purchase.
- **salary_to_hourly** — Converts compensation between annual salary, monthly pay, weekly pay, and hourly wage.
- **loan_amortization** — Loan amortization schedule with optional extra payments.
- **compound_interest** — Compound interest calculator with optional monthly contributions.
- **test_grade** — Calculates a test or exam grade from the number of correct answers and total questions.
- **square_footage** — Calculates area and perimeter for common shapes — rectangle, circle, or triangle — in both imperial and metric units.
- **unit_convert** — Universal unit converter across 10 categories.
- **hex_converter** — Convert between hex, binary, decimal, and octal with bit/byte analysis.
- **timestamp_converter** — Convert between Unix timestamps and ISO 8601 dates with relative time.
- **bmi_calculator** — Calculate BMI from weight and height with WHO classification.
- **tip_calculator** — Calculate tip and split a bill among diners.
- **date_difference** — Calculate days, weeks, months, and business days between two dates.

## Discovery Resources
- Full catalog (JSON): https://calc.engineer/api
- OpenAPI spec: https://calc.engineer/api/docs
- MCP metadata: https://calc.engineer/mcp.json
- This file: https://calc.engineer/llms.txt