Reference Data MCP Server

@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 Reference Resource Families • 1 Agent Skill

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 in one place. Look up, search, and convert across all of them, entirely offline with no API keys or rate limits.

Tools

Resources

The three reference families use four URI template routes: countries, elements, encoded timezone IDs, and an unencoded-timezone-slash route that returns retry guidance. The guide is a separate skill resource.

Reference 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.

The reference-data guide is included in plugin installs and available through MCP resource discovery or the Skills extension (skills/list and skills/get). It covers location resolution, repeated-hour disambiguation, and search-completeness gates.

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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. It serves Streamable HTTP; each client takes its own config shape.

For Claude Code:

claude mcp add --transport http reference-data-mcp-server https://reference-data.caseyjhand.com/mcp

For Cline (cline_mcp_settings.json):

{

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

For Cursor (mcp.json):

{

"mcpServers": { "reference-data-mcp-server": { "url": "https://reference-data.caseyjha