io.github.cyanheads/reference-data-mcp-server

Public Hosted Server: https://reference-data.caseyjhand.com/mcp

Tools

Ten tools grouped by domain — geo, timezone, periodic table, physical constants, unit conversion, HTTP, and web:

ref_geo_lookup

Look up a country by name, ISO alpha-2 or alpha-3 code.

• Accepts fuzzy name matching — "Brasil" and "Brazil" both resolve
• Returns full record: capital, region, subregion, official languages, currencies, calling codes, TLD, flag emoji, and IANA timezone IDs
• Lookup modes: auto (tries alpha-2, alpha-3, then name), name, alpha2, alpha3

ref_geo_search

Search and filter countries with at least one filter required.

• Filters: keyword (name, native name, capital, subregion), region, subregion, language (ISO 639-1 code or name), currency (ISO 4217 code or name)
• Returns ranked summaries (alpha-2/3, name, capital, region, primary currency, flag)
• Paginated with configurable limit (1–100); truncated flag when results are cut off

ref_timezone_lookup

Get timezone info for an IANA ID, country code, or city name.

• Partial city matching: "Tokyo" resolves to "Asia/Tokyo", "NY" to "America/New_York"
• Country code queries return all timezones observed in that country
• Optional at parameter evaluates DST state at a specific ISO 8601 moment
• Returns current offset, standard offset, DST status, abbreviations, major cities, and country codes

ref_timezone_convert

Convert a local datetime between timezones.

• Input is a local ISO 8601 datetime without offset (e.g., "2026-05-24T15:30:00")
• Accepts full IANA IDs or unambiguous city names
• Handles DST transitions with a two-pass offset refinement
• Returns source and target local datetimes with their respective UTC offsets, plus the UTC equivalent

ref_element_lookup

Look up any of the 118 periodic table elements.

• Accepts name, symbol, or atomic number
• Full property set: atomic mass (with estimated flag), electron configuration, group, period, block, category, Pauling electronegativity, density, melting and boiling points in kelvin, phase at STP, radioactivity, natural occurrence, and discovery data
• Data sourced from PubChem/IUPAC 2024; synthetic/unstable elements return null for experimentally inaccessible properties

ref_element_search

Filter elements across the full periodic table.

• Filters: category (partial match), group (1–18), period (1–7), atomic number range, atomic mass range
• At least one filter required; returns summaries with atomic number, symbol, name, mass, and category

ref_constant_lookup

Look up CODATA 2022 physical constants (~360 entries).

• Fuzzy alias matching: "speed of light", "c", "Avogadro's number", "N_A", "Planck", "h", "Boltzmann", "k_B" all resolve
• Returns value, SI unit expression, absolute and relative uncertainty, exact-definition flag, CODATA identifier, and up to 3 related constants

ref_unit_convert

Convert between units in 11 measurement domains.

• Supported: length (mm–mi), mass (mcg–t), volume (ml–m³), temperature (C/F/K/R, non-linear), speed (m/s, km/h, knot, ft/s), pressure (Pa–psi), energy (J–MWh), power (W–GW), frequency (Hz–GHz), digital storage (b–TB), angle (deg/rad/grad)
• Incompatible unit pairs return a structured error identifying the quantity mismatch
• Temperatures below absolute zero return a specific error with the Kelvin equivalent

ref_http_status

Look up HTTP status codes by number or keyword.

• Numeric queries (e.g., "404") return an exact match
• Keyword queries (e.g., "not found", "too many requests") return the closest match plus alternatives
• Returns: reason phrase, description, category (1xx–5xx), cacheability per RFC 9110, defining RFC with section reference

ref_mime_type

Look up MIME types by type string or file extension.

• Accepts "image/webp", ".webp", or "webp" interchangeably
• Extension lookups return the canonical MIME type first; additional types sharing the extension are listed as alternatives
• Returns: extensions, compressibility flag (relevant for Content-Encoding decisions), and data source (iana/apache/nginx)

Resources

All resource data is also reachable via tools. Use ref_geo_lookup, ref_element_lookup, and ref_timezone_lookup when you need flexible query modes or country search.

Features

Built on @cyanheads/mcp-ts-core:

• Declarative tool, resource, and prompt definitions — single file per primitive, framework handles registration and validation
• Unified error handling — handlers throw, framework catches, classifies, and formats
• Pluggable auth: none, jwt, oauth
• Swappable storage backends: in-memory, filesystem, Supabase, Cloudflare KV/R2/D1
• Structured logging with optional OpenTelemetry tracing
• STDIO and Streamable HTTP transports

Reference-data-specific:

• Entirely in-memory — all datasets load at startup; no runtime network calls, no API keys, no rate limits
• Works offline and in air-gapped environments
• Seven specialized services: geo (countries-list), timezone (Node.js Intl + @vvo/tzdb), elements (PubChem/IUPAC 2024, 118 elements), constants (CODATA 2022, ~360 entries), units (convert-units), HTTP status (IANA registry), MIME types (mime-db, ~1,000 types)

Agent-friendly output:

• Structured error contracts on every tool — typed reason codes (no_match, no_filters, unknown_unit, incompatible_units, below_absolute_zero, invalid_timezone, invalid_datetime) with actionable recovery hints
• Discriminated outputs where relevant — truncated flag on search results, alternatives arrays on MIME/HTTP keyword matches, atomic_mass_estimated flag on element data
• Consistent null for genuinely unknown or inapplicable values rather than absent fields

Getting started

Add the following to your MCP client configuration file:

{
  "mcpServers": {
    "reference-data-mcp-server": {
      "type": "stdio",
      "command": "bunx",
      "args": ["@cyanheads/reference-data-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with npx (no Bun required):

{
  "mcpServers": {
    "reference-data-mcp-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@cyanheads/reference-data-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with Docker:

{
  "mcpServers": {
    "reference-data-mcp-server": {
      "type": "stdio",
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-e", "MCP_TRANSPORT_TYPE=stdio",
        "ghcr.io/cyanheads/reference-data-mcp-server:latest"
      ]
    }
  }
}

For Streamable HTTP, set the transport and start the server:

MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 bun run start:http
# Server listens at http://localhost:3010/mcp

Prerequisites

• Bun v1.3.0 or higher (or Node.js v24+).
• No API keys required — this server is entirely self-contained.

Installation

1. Clone the repository:

git clone https://github.com/cyanheads/reference-data-mcp-server.git

2. Navigate into the directory:

cd reference-data-mcp-server

3. Install dependencies:

bun install

4. Configure environment (optional):

cp .env.example .env
# edit .env if you want to override transport or logging defaults

Configuration

No API keys are required. All configuration is optional overrides of framework defaults.

See .env.example for the full list of optional overrides.

Running the server

Local development

# One-time build
bun run rebuild

# Run the built server
bun run start:stdio
# or
bun run start:http

bun run devcheck   # Lint, format, typecheck, security
bun run test       # Vitest test suite
bun run lint:mcp   # Validate MCP definitions against spec

Docker

docker build -t reference-data-mcp-server .
docker run --rm -p 3010:3010 reference-data-mcp-server

The Dockerfile defaults to HTTP transport, stateless session mode, and logs to /var/log/reference-data-mcp-server. OpenTelemetry peer dependencies are installed by default — build with --build-arg OTEL_ENABLED=false to omit them.

Project structure

Development guide

See CLAUDE.md for development guidelines and architectural rules. The short version:

• Handlers throw, framework catches — no try/catch in tool logic
• Use ctx.log for request-scoped logging, ctx.state for tenant-scoped storage
• Register new tools and resources directly in src/index.ts
• Data integrity: validate raw → normalize to domain type → return output schema; never fabricate missing fields

Contributing

Issues and pull requests are welcome. Run checks and tests before submitting:

bun run devcheck
bun run test

License

Apache-2.0 — see LICENSE for details.