@cyanheads/reference-data-mcp-server

Look up countries, timezones, periodic table elements, physical constants, units, HTTP status codes, and MIME types via MCP. STDIO or Streamable HTTP.

10 Tools • 3 Resources

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Tools

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

Tool	Description
ref_geo_lookup	Look up a country by name, ISO alpha-2, or alpha-3 code. Returns capital, region, languages, currencies, calling codes, TLD, flag, and IANA timezone IDs.
ref_geo_search	Search and filter countries by region, subregion, language, currency, or free-text keyword.
ref_timezone_lookup	Get timezone info by IANA ID, country code, or partial city/region name. Returns current and standard UTC offsets, DST status, and major cities.
ref_timezone_convert	Convert a local datetime from one timezone to another, with visible UTC offsets for both sides.
ref_element_lookup	Look up a periodic table element by name, symbol, or atomic number. Full property set including atomic mass, electron configuration, electronegativity, density, melting/boiling points, and discovery data.
ref_element_search	Filter elements by category, group, period, atomic number range, or atomic mass range.
ref_constant_lookup	Look up a CODATA 2022 physical constant by name, symbol, or alias. Returns value, SI unit, uncertainty, and related constants.
ref_unit_convert	Convert a numeric value between compatible units of measure (length, mass, volume, temperature, speed, pressure, energy, power, frequency, digital storage, angle).
ref_http_status	Look up an HTTP status code by number or keyword. Returns reason phrase, description, category, cacheability, and RFC reference.
ref_mime_type	Look up a MIME type by type string or file extension. Returns canonical type, extensions, compressibility, and data source.

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

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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

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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

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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

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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

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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

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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

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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

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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

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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)

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Resources

Type	Name	Description
Resource	ref://countries/{alpha2}	Full country record by ISO alpha-2 code (e.g., ref://countries/DE).
Resource	ref://elements/{number}	Full element record by atomic number (e.g., ref://elements/6 for Carbon).
Resource	ref://timezones/{iana_id}	Timezone info by IANA ID with slashes URL-encoded as %2F (e.g., ref://timezones/America%2FNew_York).

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.

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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

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Getting started

Add the following to your MCP client configuration file:

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

Or with npx (no Bun required):

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

Or with Docker:

{
  "mcpServers": {
    "reference-data": {
      "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

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Configuration

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

Variable	Description	Default
MCP_TRANSPORT_TYPE	Transport: stdio or http.	stdio
MCP_HTTP_PORT	Port for HTTP server.	3010
MCP_HTTP_HOST	Host for HTTP server.	127.0.0.1
MCP_AUTH_MODE	Auth mode: none, jwt, or oauth.	none
MCP_LOG_LEVEL	Log level (RFC 5424): debug, info, notice, warning, error.	info
LOGS_DIR	Directory for log files (Node.js only).	<project-root>/logs
OTEL_ENABLED	Enable OpenTelemetry instrumentation (spans, metrics, completion logs).	false

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

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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.

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Project structure

Directory	Purpose
src/index.ts	createApp() entry point — registers tools/resources and inits services.
src/data/	Static datasets (periodic table, physical constants, HTTP status codes).
src/mcp-server/tools/	Tool definitions (*.tool.ts).
src/mcp-server/resources/	Resource definitions (*.resource.ts).
src/services/	Domain service integrations (geo, timezone, elements, constants, units, http-status, mime).
tests/	Unit tests mirroring src/.
docs/	Generated docs (tree.md, design.md).
changelog/	Per-version changelog files.

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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

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Contributing

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

bun run devcheck
bun run test

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License

Apache-2.0 — see LICENSE for details.