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Calcgrid
com.tttkmbb/calcgrid in the official MCP registry.
Endpoint https://tttkmbb.com/mcp.
The registry describes it as: China working-day data, UK bank holidays, IANA time zones and deterministic business deadlines.
We read its 200 tools on 2026-10-26. 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
search_calculators list_calculators list_calculator_categories list_working_day_calendars get_calculator_schema run_calculator convert_units list_units calculate_business_deadline check_china_working_day add_china_working_days count_china_working_days check_uk_working_day add_uk_working_days count_uk_working_days check_global_working_day add_global_working_days count_global_working_days convert_solar_to_lunar convert_lunar_to_solar list_solar_terms resolve_local_time list_time_zone_transitions convert_time_zone calculate_loan_payment compare_loans check_global_public_holiday_working_day add_global_public_holiday_working_days count_global_public_holiday_working_days check_global_reference_working_day add_global_reference_working_days count_global_reference_working_days calculate_compound_interest calculate_mortgage_payment calculate_tip calculate_amortization_schedule calculate_bmi calculate_bmr calculate_tdee calculate_running_pace calculate_percentage calculate_percentage_change solve_quadratic_equation calculate_fraction_arithmetic calculate_circle_properties calculate_descriptive_statistics calculate_t_test convert_temperature calculate_kinetic_energy solve_ohms_law calculate_molar_mass calculate_age calculate_date_difference check_singapore_working_day add_singapore_working_days count_singapore_working_days check_australia_working_day add_australia_working_days count_australia_working_days check_us_federal_working_day and 140 more
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[](https://lazaretto.dev/mcp-registry/com-tttkmbb-calcgrid)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.