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calc.engineer
engineer.calc/calc in the official MCP registry.
Endpoint https://calc.engineer/mcp.
The registry describes it as: 88 free engineering calculators: RF link budgets, LoRa/Meshtastic, PCB, solar, homelab. Keyless.
We read its 89 tools on 2026-10-28. Nothing in them matched our tool-poisoning rules. It also sets server instructions, text a client puts in front of the model on connect; those were read too.
A clean read means these rules found nothing, not that the server is harmless. A server can change its tools at any time, which is why the index reads it again every week.
Tools it advertises
fspl link_budget dipole microstrip dbm_convert noise_figure_cascade vswr attenuator_pi attenuator_tee fresnel_zone wavelength_freq spice_template spice_simulate lora_airtime snr_margin channel_utilization lora_range_estimate lora_sensitivity duty_cycle_budget meshtastic_range eirp_compliance meshtastic_power lora_param_optimizer zfs_capacity zfs_ram tcp_throughput wireguard_mtu subnet_calculator raid_iops power_cost cooling_btu rack_capacity network_bandwidth thermal_enclosure heatsink_cfd pcb_thermal battery_life wire_gauge solar_sizing ups_runtime mah_to_wh watts_to_amps voltage_drop battery_charge_time solar_load_audit solar_roi battery_autonomy string_sizing generator_offset wire_ampacity inverter_sizing pcb_layout voltage_divider rc_filter lc_resonance impedance_match trace_width ohms_law resistor_color_code led_resistor and 29 more
Run this server? Show the check in your README
The badge reflects the latest weekly read: 
[](https://lazaretto.dev/mcp-registry/engineer-calc-calc)How this was checked
Lazaretto connects to the endpoint the way any MCP client does, asks the server to introduce itself and list its tools, and reads every name, description, parameter schema and server instruction for tool poisoning: hidden directive blocks, orders to read local secrets, parameters built to carry secrets or the conversation out, orders that redirect another server's tools, and invisible characters. It never calls a tool. What we found across the registry.
To run the same check every time Claude Code adds a server, install the free lazaretto-guard plugin. Browse every server in the index.