@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

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

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Overview

Countries, timezones, periodic table elements, physical constants, units, HTTP status codes, and MIME types — all served from static, in-memory datasets, entirely offline with no API keys or rate limits. Look up, search, and convert across these domains from any MCP client. Runs as a stdio process, a local Streamable HTTP server, or the public hosted endpoint above.

Tools

Tool	Description
ref_geo_lookup	Look up a country by name, ISO alpha-2, or alpha-3 code.
ref_geo_search	Search and filter countries by region, subregion, language, or currency.
ref_timezone_lookup	Get timezone info by IANA ID, country code, or city name.
ref_timezone_convert	Convert a local datetime from one timezone to another.
ref_element_lookup	Look up a periodic table element by name, symbol, or atomic number.
ref_element_search	Filter periodic table elements by category, group, period, or property range.
ref_constant_lookup	Look up a CODATA 2022 physical constant by name, symbol, or alias.
ref_unit_convert	Convert a numeric value between compatible units of measure.
ref_http_status	Look up an HTTP status code by number or keyword.
ref_mime_type	Look up a MIME type by type string or file extension.

Resources

Resource	Description
ref://countries/{alpha2}	Full country record by ISO alpha-2 code.
ref://elements/{number}	Full element record by atomic number.
ref://timezones/{iana_id}	Timezone info by IANA ID (slashes percent-encoded as %2F).

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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Capability reference

ref_geo_lookup _tool

• Accepts fuzzy name matching ("Brasil" resolves to "Brazil"); a fuzzy hit adds an enrichment notice naming the canonical result
• Lookup modes: auto (alpha2 → alpha3 → name), name, alpha2, alpha3; numeric ISO codes are not supported
• Returns capital, region/subregion, languages, currencies, calling codes, TLD, flag emoji, and IANA timezone IDs

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ref_geo_search _tool

• At least one filter required (no_filters error otherwise): keyword (name, native name, capital, subregion), region, subregion, language (ISO 639-1 code or name), or currency (ISO 4217 code or name)
• Limit 1–100 (default 20); truncated flag and totalMatches count when results are cut off
• Empty result set returns a notice echoing the applied filters

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ref_timezone_lookup _tool

• Lookup modes: auto (IANA ID → country code → city name), iana, country; partial city matching ("Tokyo" → "Asia/Tokyo", "NY" → "America/New_York")
• Country-code queries return every timezone observed in that country
• Optional at (ISO 8601) evaluates DST state at a specific moment instead of now; malformed values raise invalid_at
• Returns current/standard UTC offsets, DST status and abbreviations, major cities, and country codes

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ref_timezone_convert _tool

• datetime must be a local ISO 8601 string without an offset (regex-enforced, e.g. 2026-05-24T15:30:00); from_tz/to_tz accept full IANA IDs or unambiguous city names
• Rejects out-of-range calendar dates and spring-forward DST gaps as invalid_datetime; unrecognized zones as invalid_timezone
• Returns source and target local datetimes with their respective UTC offsets, plus the UTC equivalent

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ref_element_lookup _tool

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

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ref_element_search _tool

• At least one filter required (no_filters error otherwise): category (partial match), group (1–18), period (1–7), atomic-number range, or atomic-mass range
• Valid categories: alkali metal, alkaline earth metal, transition metal, post-transition metal, metalloid, reactive nonmetal, noble gas, lanthanide, actinide
• Returns summaries (atomic number, symbol, name, mass, category) plus a totalMatches count and a notice when nothing matches

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ref_constant_lookup _tool

• Fuzzy alias matching: "speed of light", "c", "Avogadro's number", "N_A", "Planck", "h", "Boltzmann", "k_B" all resolve against 32 CODATA 2022 constants
• match_strategy discriminates how the query resolved: exact_symbol, exact_name, or fuzzy (closest candidate — verify before reuse)
• Returns value, SI unit expression, absolute/relative uncertainty (exact flag for defined constants), CODATA identifier, and up to 3 related constants

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ref_unit_convert _tool

• 11 measurement domains: length, mass, volume, temperature (non-linear C/F/K/R), speed, pressure, energy, power, frequency, digital storage, angle
• Mass mt is the metric tonne (1000 kg); t is the US short ton (907.18 kg) — distinct units, easily confused
• Typed errors: incompatible_units (mismatched quantities), unknown_unit (unrecognized abbreviation), below_absolute_zero (with the Kelvin equivalent)

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ref_http_status _tool

• 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, and the defining RFC with section reference

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ref_mime_type _tool

• 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, a compressibility flag (relevant for Content-Encoding decisions), and the data source (iana/apache/nginx)

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ref://countries/{alpha2} _resource

• Full country record as application/json — same fields as ref_geo_lookup
• alpha2 accepts either case; an unmatched code returns a notFound error

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ref://elements/{number} _resource

• Full element record as application/json — same fields as ref_element_lookup
• number must be an integer string 1–118; out-of-range or unmatched values return notFound

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ref://timezones/{iana_id} _resource

• Timezone record as application/json — same fields as ref_timezone_lookup, plus evaluated_at
• Slashes in the IANA ID must be percent-encoded as %2F (e.g. America%2FNew_York); an unencoded slash matches a separate catch-all that returns an actionable error with the correctly encoded URI

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Features

Built on @cyanheads/mcp-ts-core: stdio and Streamable HTTP transports, pluggable auth (none / jwt / oauth), swappable storage (in-memory, filesystem, Supabase, Cloudflare KV/R2/D1), structured logging with optional OpenTelemetry tracing.

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, 32 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, invalid_at) 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, match_strategy on constant lookups
• Consistent null for genuinely unknown or inapplicable values rather than absent fields

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Getting started

Public Hosted Instance

A public instance is available at https://reference-data.caseyjhand.com/mcp — no installation required. Point any MCP client at it via Streamable HTTP:

{
  "mcpServers": {
    "reference-data-mcp-server": {
      "type": "streamable-http",
      "url": "https://reference-data.caseyjhand.com/mcp"
    }
  }
}

Self-Hosted / Local

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 v1.4.0 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_SESSION_MODE	Session mode: stateful, stateless, or auto (schema default auto resolves to stateful).	stateless
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 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.