"Free and open-source coding assistants" matching MCP servers:

An open engine that gives AI persistent, reusable UI components with a writable component registry, versioned data storage, and a shell runtime, enabling AI to create, save, and reuse single-purpose apps.

Open Ephemeris is a high-precision astrology API with an MCP server exposing 116+ endpoints across natal charts, transits, synastry, Human Design, BaZi, solar returns, and much more.

Provides real-time air quality data (US AQI, PM2.5, PM10, ozone, NO2, SO2, CO) for any city via natural language, using free Open-Meteo data and a single tool.

Gives AI assistants live access to US prescription drug prices by pharmacy with observation dates, the free discount card, and vetted US equivalents of foreign-brand medicines, all through the Model Context Protocol.

Daash connects Garmin Connect to ChatGPT and Claude. Your assistant reads your runs, splits, sleep, HRV, Body Battery and recovery, and writes structured workouts and whole training plans to your Garmin calendar, so they're on your watch at the next sync. Free, hosted, open source. Works on free Claude.

Serves Claude Desktop a unified, actionable read of Google Calendar and Google Tasks, surfacing overdue items first, then the day's events, free slots, and open tasks, with explicit-request-only write tools for creating, updating, completing, and deleting. Google stays the sole source of truth with no server-side storage beyond the OAuth token and a 30-second read cache.

Local serial and USB hardware access for coding agents, with typed YAML protocol commands, checksum validation, audited writes, lossless captures, hardware-free replay, and MCP App visualizations. Runs locally over stdio; live hardware use requires a serial device connected to the same machine.

Open-source MCP server that lets AI agents control 3D printers. 353 tools for OctoPrint, Moonraker, Bambu Lab, Prusa Link, and Elegoo — search model marketplaces, generate 3D models from text, slice STL files, queue prints, monitor with camera vision, and manage multi-printer fleets. Install via pip install kiln3d.

MCP server that resolves postal/ZIP codes to place names, states, and coordinates using Zippopotam.us. Free, no API key required.

Enables real-time domain registration lookups via RDAP, including availability, expiration, and registrar details, with no API key required. Supports natural language queries like 'is example.com available?' or 'when does example.com expire?'.

Enables AI assistants to bulk-check hundreds of brainstormed domain names in a single call, reporting which are available, taken, or reserved along with buy links and prices from multiple registrars. It runs locally via DNS, RDAP, and WHOIS lookups, with optional registrar API keys for confirming availability and premium pricing.

MCP server for creating and editing diagrams using draw.io. Allows generating diagrams from Mermaid or XML, searching shapes, and opening them in draw.io for export.

Enables users to draw GIS geometry on an interactive map and get clean, validated GeoJSON to hand off to other GIS MCP servers such as FEMA flood screening and USGS hydrography.

Gives Claude read-only access to your ESPN fantasy football team, including roster, weekly matchup, free agents, and player profiles.

MCP server that lets agents create, display, and export rich UI widgets (cards, dashboards, charts, forms) inline in conversations, with interactive iframe support in MCP Apps hosts and PNG image fallback for other clients.

Enables generation of chemical structures, reactions, spectra, titration curves, 3D models, and more from natural language or SMILES, using RDKit for offline rendering and supporting formats like PNG, SVG, CDXML, and Anki decks.

Vacation rental software. A signed stay offer on the host's own domain. Agents discover a host domain, verify an Ed25519-signed offer (VRP), and send the guest to that domain to book and pay the host. Do not compare hosts or prices. HemmaBo + VRP, 6 runtime tools: 2 HemmaBo tools, 2 host onboarding tools, and 2 VRP verification tools. Not an OTA. Not a marketplace.

Local-first crypto portfolio aggregation across exchanges (Bybit, Binance), EVM and Solana wallets, and Polymarket. Read-only credentials, runs as a local MCP server. Data aggregation only, not financial advice.

Enables currency conversion and exchange rate lookups using real ECB reference rates, free and without an API key. Supports natural language queries like 'convert 100 USD to EUR' or 'what's the exchange rate between GBP and JPY?'.

Provides real, official public holiday data for ~100 countries with tools to list holidays for a year and check if a specific date is a holiday. Free, no API key required, powered by Nager.Date.