fcc-spectrum-mcp-server

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Overview

US radio spectrum licensing from the FCC's Universal Licensing System, searchable offline. Look up a callsign, licensee, or market; read a license's sites, antennas, frequencies, and microwave paths; find transmitters near a point; and see who's authorized on any frequency or band. Covers land mobile, microwave, cellular, paging, amateur, and more; full-power broadcast stations and satellite earth stations aren't included. No API key required.

Tools

Tool	Description
fcc_spectrum_search_licenses	Search licenses and spectrum leases by callsign, licensee name, FRN, market code, radio service, status, or licensee state.
fcc_spectrum_get_license	Read one license or lease in full by callsign or USI: licensee, status and dates, locations, antennas, frequencies with emissions, microwave paths, market blocks, and lease links.
fcc_spectrum_find_transmitters	Find FCC-licensed sites within a radius of a coordinate, nearest first, with their filed roles and authorized frequencies.
fcc_spectrum_search_frequencies	Find site assignments and market-area spectrum blocks whose occupied band overlaps a frequency or band.
fcc_spectrum_list_reference	Decode ULS codes (radio services, station classes, statuses, location and antenna types, applicant types, operator classes) and report index coverage and freshness.

Resources

Resource	Description
fcc-spectrum://license/{callsign}	One license or lease by callsign as JSON — the first page fcc_spectrum_get_license returns.
skill://fcc-spectrum-guide/SKILL.md	Workflow guidance for ULS investigations: completeness checks, identifiers, shared sites, market geography, leases, and microwave paths.

License records are also reachable via fcc_spectrum_get_license. The investigation guide is available to clients through resources/list and resources/read.

Capability reference

fcc_spectrum_search_licenses _tool

• Filters: callsign, licensee (every word must match the start of a word in the name), frn, market_code (a geographic-area license's market, matched exactly: PEA016, CMA020, D06037, NW; pea16 reads as PEA016), radio_service, and state (the licensee's mailing state) — at least one required; status narrows to A (default), C, E, L, P, T, X, or any
• Positive integer limit (default 25, capped at 100) with cursor paging; each row carries the usi to pass to fcc_spectrum_get_license, plus isLease, licenseeRedacted, and location and frequency counts
• Typed errors: no_criteria, unknown_radio_service, service_not_indexed, invalid_cursor, index_not_ready

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fcc_spectrum_get_license _tool

• Exactly one of callsign or usi (identifier_required otherwise); a callsign shared by several records returns the active one, else the most recent, and lists the others in otherCallsignRecords
• Pages large records: whole locations up to 50 sites, 100 antennas, and 100 microwave paths (a location larger than that is listed alone), up to 100 leases, and max_frequencies frequency rows (positive integer, default 100, capped at 1000) per call; nextLocationOffset and nextLeaseOffset feed location_offset and lease_offset on the next call
• Microwave paths (FCC PA records) are listed in paths under the antenna that transmits them: path number, type, passive flag, and receiving callsign as filed, and a receive end with its location and antenna numbers, coordinates when the license files exactly one valid site under the receive number, siteCount when it files none or several, and antennaFiled: false when no antenna record matches. pathTotal counts the record's paths across all locations (absent on an index built before paths were indexed, until mirror:init rebuilds it), and when more locations follow, the notice reports the paths listed against it
• location_number starts the locations at a site's locationNumber from fcc_spectrum_find_transmitters or fcc_spectrum_search_frequencies; combined with a nonzero location_offset it fails (location_start_conflict)
• A miss returns found: false with guidance and up to 5 callsign-prefix candidates, not an error; technicalRetained: false marks a record whose status keeps no sites or frequencies

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fcc_spectrum_find_transmitters _tool

• latitude / longitude as decimal degrees or DMS strings, radius_km 0.1–100 (default 5); optional frequency_low / frequency_high in unit (kHz, MHz default, GHz), radio_service, location_type (one ULS location type code, case-insensitive: F keeps fixed sites only, M mobile and T temporary-fixed areas), and status (A default, L, X, or any for all three)
• Sites nearest first, positive integer limit (default 25, capped at 100) with cursor paging; each site lists up to max_frequencies_per_site frequencies (positive integer, default 10, capped at 50), with frequencyCount carrying the full count
• Each site carries locationTypeCode, locationTypeLabel, radiusKm, locationClassCode, and locationClassLabel when filed; a mobile or temporary-fixed area is returned at its filed center, and distanceKm measures to that center. location_class (case-insensitive C, L, P, R, or T) keeps one FCC class; results describe authorization, not actual on-air activity
• Typed errors: invalid_frequency_range, unknown_radio_service, service_not_indexed, invalid_cursor, index_not_ready

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fcc_spectrum_search_frequencies _tool

• frequency_low required, frequency_high optional, in unit; a site assignment matches when its occupied band (widened by its emission bandwidth) overlaps the query, a market block when its filed edges do; kind is site, market, or both (default)
• Narrow by state, radio_service, licensee, frn, market_code, and status (A default, L, X, any); positive integer limit (default 50, capped at 200) with cursor paging, frequency ascending; each row's kind says whether it is a site assignment or a market block
• market_code and frn filter site rows and market rows alike; an frn search returns individual licensees redacted. Single-site rows carry locationTypeCode, locationTypeLabel, radiusKm, locationClassCode, and locationClassLabel when filed; shared-number rows and market blocks omit them
• Typed errors: invalid_frequency_range, unknown_radio_service, service_not_indexed, invalid_cursor, index_not_ready

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fcc_spectrum_list_reference _tool

• topic: radio_services, station_classes, license_statuses, location_types, antenna_types, applicant_types, operator_classes, or coverage; filter narrows radio services and station classes to entries containing every token in their code and label, with case/accent folding and punctuation separating tokens
• A searchable filter must contain an ASCII letter or digit (invalid_filter otherwise); blank means unset. Other topics ignore the filter and say so
• Decode a station class with {"topic":"station_classes","filter":"FXO"} (FXO is Operational Fixed, FB2 Mobile Relay, MO Mobile). Labels come from a bundled 266-code table of the FCC's uls_code_definitions_20240718.txt (archived copy); an unmapped code returns no entries. These are licensed categories, not actual on-air activity
• coverage reports index.status (none, building, ready), per-group record, site, and frequency counts with snapshot times, and whether redaction is on; it works before the index is built. index.antennaCoverageIncomplete: true marks an older index that dropped unnumbered antennas, and index.pathCoverageIncomplete: true one built before microwave paths were indexed; bun run mirror:init rebuilds either

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fcc-spectrum://license/{callsign} _resource

• The first page of fcc_spectrum_get_license (up to 100 frequency rows, with its microwave paths) as application/json, with dataAsOf, totals, and a notice naming the tool call that reads the rest; cached 1 hour
• Typed errors: index_not_ready, license_not_found

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.

FCC ULS-specific:

• Keyless and local at request time — every query reads the SQLite index; network access is needed only to build and refresh it
• Occupied-band frequency matching — each assignment's band is widened by the bandwidth parsed from its emission designators, so a query near a wide channel's edge still finds it
• Spectrum leases are first-class records — isLease marks them, the licensee shown is the lessee, and lease links are listed in both directions
• Site state is derived from coordinates when the filing leaves it blank (common for microwave and BRS/EBS), and flagged stateFromCoordinates
• Individual licensees are redacted by default, and contact details are never ingested — see Individual-licensee redaction

Agent-friendly output:

• Freshness and filter echo — every data response carries dataAsOf, and search tools echo appliedFilters
• Truncation disclosure — truncated, shown, cap, and totalCount plus a notice naming the next call, so a partial page is never read as the whole; output budgets above a ceiling clamp to it with a notice naming requested and effective values
• Absent stays absent — fields ULS leaves blank are omitted, coordinates that fail validation are kept as DMS text (coordinatesDms), and all-zero placeholder coordinates are dropped
• Discriminated output — found, kind, isLease, licenseeRedacted, and technicalRetained let callers branch on data, not string parsing

Getting started

Connect to the hosted instance, no install:

claude mcp add --transport http fcc-spectrum-mcp-server https://fcc-spectrum.caseyjhand.com/mcp

The hosted index is rebuilt weekly and refreshed daily, with individual licensees redacted.

Or run it locally against an index built with First-run setup:

claude mcp add fcc-spectrum-mcp-server -e FCC_SPECTRUM_MIRROR_DIR=/path/to/fcc-uls -- bunx @cyanheads/fcc-spectrum-mcp-server

For other clients, add this to the MCP config file:

{
  "mcpServers": {
    "fcc-spectrum-mcp-server": {
      "command": "bunx",
      "args": ["@cyanheads/fcc-spectrum-mcp-server"],
      "env": { "FCC_SPECTRUM_MIRROR_DIR": "/path/to/fcc-uls" }
    }
  }
}

FCC_SPECTRUM_MIRROR_DIR must name the directory mirror:init built. Use an absolute path: MCP clients choose the process's working directory. Until the first build completes, data tools fail with index_not_ready; fcc_spectrum_list_reference with topic coverage reports the build state.

For Docker or a source build, see Running the server.

First-run setup

The index is built from the FCC's public ULS bulk files at data.fcc.gov — weekly full snapshots per service group, plus daily incrementals. On the default groups a build downloads about 1.1 GB of zips, one at a time; a measured build produced 3,270,502 license records and an index of about 1.8 GB in about 3 minutes.

Build it once from a source checkout after bun run build (see Running the server), from an installed package, or with the Docker image:

# Download the weekly snapshots and build the index (resumable; skips when nothing is newer)
FCC_SPECTRUM_MIRROR_DIR=/path/to/fcc-uls bun run mirror:init

# Check it: SQLite integrity plus per-file line counts against the FCC's counts files
FCC_SPECTRUM_MIRROR_DIR=/path/to/fcc-uls bun run mirror:verify

# Apply the daily incrementals published since the last build
FCC_SPECTRUM_MIRROR_DIR=/path/to/fcc-uls bun run mirror:refresh

Each mirror:* script runs a compiled entry under dist/cli/ on Bun. From an npm install, run the scripts from the package directory, or call an entry directly: FCC_SPECTRUM_MIRROR_DIR=/path/to/fcc-uls bun node_modules/@cyanheads/fcc-spectrum-mcp-server/dist/cli/mirror-init.js (likewise mirror-verify.js and mirror-refresh.js).

With Docker, run the same commands against the volume: docker run --rm -v fcc-uls:/usr/src/app/.mirror ghcr.io/cyanheads/fcc-spectrum-mcp-server:latest bun run mirror:init.

Keeping it current:

• HTTP transport. The server schedules the weekly rebuild on Sundays at 16:00 and the daily refresh at 17:00, in the process's local time (the Docker image runs in UTC; the FCC publishes snapshots Sunday morning US Eastern). Refresh checks the available daily publication dates for gaps and overwritten files. When they cannot cover the checkpoint, it runs the weekly rebuild and retries refresh; if no newer snapshot is available, the job reports failure until recovery is possible. Neither job runs until mirror:init has published a first index. Each job runs in a child process on the server's runtime, so queries and /healthz keep answering while it writes, and its log lines appear in the server log; on shutdown a running job is stopped and resumes at the next run.
• stdio. Nothing is scheduled. Run mirror:refresh daily and mirror:init weekly from cron or another scheduler; daily files never remove licenses, so removals arrive with the weekly rebuild.
• Disk. A rebuild writes a new generation beside the one being served, so leave room for a second index plus the largest zip (about 420 MB). Older generations are deleted at the start of the next rebuild.
• Concurrency. An ingest lock lets one mirror:init, mirror:refresh, or scheduled job write at a time; an interrupted mirror:init resumes from its last completed step when rerun.

Configuration

Variable	Description	Default
FCC_SPECTRUM_MIRROR_DIR	Directory holding the index and its build files. Use an absolute path.	.mirror/fcc-uls
FCC_SPECTRUM_SERVICES	Comma-separated weekly service groups to index, case-insensitive. Opt-in: gmrs, ship, aircr. An unknown name fails startup and lists the valid set.	LMpriv,LMcomm,LMbcast,micro,cell,market,paging,coast,mdsitfs,amat
FCC_SPECTRUM_REDACT_INDIVIDUALS	Redact individual licensees and trustee names and exclude individuals from name search. Only false, 0, no, or off disables it.	true
FCC_SPECTRUM_BASE_URL	ULS bulk file host root, read only when building or refreshing the index.	https://data.fcc.gov/download/pub/uls
MCP_TRANSPORT_TYPE	Transport: stdio or http.	stdio
MCP_SESSION_MODE	Session mode: auto (resolves to stateful), stateful, or stateless.	stateless
MCP_HTTP_PORT	Port for the HTTP server.	3010
MCP_HTTP_ENDPOINT_PATH	HTTP endpoint path where the MCP server is mounted.	/mcp
MCP_AUTH_MODE	Auth mode: none, jwt, or oauth.	none
MCP_LOG_LEVEL	Log level (RFC 5424).	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.

Service groups

The FCC splits its weekly snapshots into service groups. Adding a group takes effect at the next mirror:init; a removed group drops out at the next weekly rebuild.

Group	Contents	Indexed
LMpriv	Private land mobile (public safety, business, industrial)	default
LMcomm	Commercial land mobile	default
LMbcast	Broadcast auxiliary land mobile	default
micro	Point-to-point microwave	default
cell	Cellular	default
market	Market-area wireless (PCS, AWS, 700 MHz, 3.45 and 3.7 GHz, and other auctioned blocks)	default
paging	Paging	default
coast	Coast stations	default
mdsitfs	Broadband Radio Service and Educational Broadband Service (BRS/EBS)	default
amat	Amateur radio	default
gmrs	General Mobile Radio Service — licensee records only	opt-in
ship	Ship stations — licensee records only	opt-in
aircr	Aircraft stations — licensee records only	opt-in

Individual-licensee redaction

ULS records name the person behind many licenses, amateur and otherwise: individuals also hold land mobile, paging, and microwave licenses. FCC_SPECTRUM_REDACT_INDIVIDUALS is on by default and fails safe:

• A record is an individual's when its applicant type is I, or blank in the amateur and GMRS services. A blank type or type H (Other) in any service also counts when the filing carries a person's name parts, or when the licensee name contains no organization word (Inc, County, Church, Wireless, …), so an organization named without one is redacted too. Its licensee name is then null with licenseeRedacted: true, and its licensee city, its sites' street addresses, and its site names are omitted, since some individuals file their own name as a site name.
• Trustee names are withheld on every license, since a trustee is always a person.
• Licensee name search excludes individuals, and the response notice says so. A callsign, USI, or FRN lookup still returns the record, redacted.
• Site coordinates, city, county, state, and technical data stay: they are the spectrum record.
• Redaction applies when a response is built, so changing the setting needs a restart, not a rebuild.

Licensee mailing street addresses, ZIP codes, PO boxes, attention lines, phone numbers, fax numbers, and email addresses are never ingested, for anyone.

Known limitations

• Dense-band frequency searches return partial pages. Over a crowded band (all of 150–174 MHz, or the whole spectrum), a page can hold fewer rows than limit and still carry nextCursor, and totalCount is then a lower bound (totalIsLowerBound: true). Narrow with state, radio_service, licensee, frn, or market_code to keep the exact count.
• Sites, frequencies, and market blocks are kept only for live licenses (A active, L pending legal, X term pending). Expired, cancelled, and terminated records keep their licensee, status, dates, and lease links.
• Market blocks match by state, not by county. state matches a market block when the FCC's market-area definitions place its market in that state (a multi-state market matches each of its states), when its market name carries the state code, or when its license files a site there; nothing maps a county or a coordinate to the markets covering it. Nationwide and Gulf of Mexico markets match no state, and Tribal land (TL) and MVDDS (MVD) markets with no state code in the name are skipped; market_code without state reaches any of them.
• Radius search matches an operating area by its center. ULS files mobile and temporary-fixed locations as a center and a radius of operation. fcc_spectrum_find_transmitters returns such an area at its center, with radiusKm, when the center lies within radius_km; it does not match an area because the search point falls inside it. Locations filed without coordinates, as most mobile, temporary, itinerant, and control-station locations are, are not returned.
• Derived states are approximate near borders, within about a kilometer of a state line; territories other than Puerto Rico get no derived state.
• Removals lag up to a week. Daily files never delete licenses; the weekly rebuild does. A refresh gap longer than the daily window forces a full rebuild.
• Priority Access Licenses are not found by frequency. ULS files each 3.5 GHz PAL as a 10 MHz channel width with no frequency; list them with fcc_spectrum_search_licenses and radio_service PL.
• Frequencies at a shared location number cannot be tied to a site. ULS files frequencies against the location number, so when a license files several sites under one number, no frequency can be placed at a single site.
• Redaction is per record. A person who also holds licenses filed under a non-individual applicant type appears by name on those records, which carry the same FRN.
• Station class labels use a bundled FCC snapshot. Technical responses preserve filed codes; fcc_spectrum_list_reference with topic: "station_classes" and filter decodes known codes. A newer or unknown code may have no bundled label.
• Coordinates are NAD83 as filed, with no datum shift.
• A few implausible emission bandwidths pass. A designator 20% of its frequency or wider is ignored as a filing error; narrower implausible filings are taken as filed.

Running the server

Prerequisites

• Bun v1.4 or higher (or Node.js v24+). bun:sqlite is built into Bun; under Node, install better-sqlite3 beside the server (declared as an optional peer dependency).
• Disk for the index at FCC_SPECTRUM_MIRROR_DIR: about 1.8 GB on the default groups, plus rebuild room as above.
• Network access to data.fcc.gov when building or refreshing the index. Queries need none.

Installation

For local development, or to build the index from source:

1. Clone the repository:

git clone https://github.com/cyanheads/fcc-spectrum-mcp-server.git

2. Navigate into the directory:

cd fcc-spectrum-mcp-server

3. Install dependencies:

bun install

4. Build the server, which also compiles the mirror:* entries:

bun run build

5. Build the index (see First-run setup):

FCC_SPECTRUM_MIRROR_DIR=/path/to/fcc-uls bun run mirror:init

Local development

• Build and run:

  # One-time build
  bun run rebuild
  
  # Build the index (see First-run setup)
  bun run mirror:init
  
  # Run the built server
  bun run start:stdio
  # or
  bun run start:http
  

• Run checks and tests:

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

Docker

# Build the index once against the volume:
docker run --rm -v fcc-uls:/usr/src/app/.mirror ghcr.io/cyanheads/fcc-spectrum-mcp-server:latest bun run mirror:init
# Serve over HTTP:
docker run --rm -p 3010:3010 -v fcc-uls:/usr/src/app/.mirror ghcr.io/cyanheads/fcc-spectrum-mcp-server:latest

The image defaults to HTTP transport with stateless sessions, includes the mirror:* CLI, and logs to /var/log/fcc-spectrum-mcp-server. For stdio, use docker run -i --rm -e MCP_TRANSPORT_TYPE=stdio -v fcc-uls:/usr/src/app/.mirror ghcr.io/cyanheads/fcc-spectrum-mcp-server:latest. Build locally with docker build -t fcc-spectrum-mcp-server .. OpenTelemetry peer dependencies are installed by default; build with --build-arg OTEL_ENABLED=false to omit them.

Project structure

Directory	Purpose
src/index.ts	createApp() entry point — registers tools, resources, and the skill directory, inits the index service, and starts the ingest schedule under HTTP transport.
src/config	Server environment variable parsing and validation with Zod.
src/mcp-server/tools	Tool definitions (*.tool.ts), shared input schemas, and format helpers.
src/mcp-server/resources	Resource definitions (*.resource.ts).
src/services/uls	ULS service — bulk client, record parsers, ingester, index generations, read path with redaction, and the ingest schedule with the job process it spawns.
src/cli	Index lifecycle CLI — mirror:init, mirror:refresh, mirror:verify — compiled to dist/cli/.
tests/	Unit and integration tests mirroring src/, with fixture ULS records.
skills/	Published investigation guide, served as an MCP resource.

Development guide

See CLAUDE.md/AGENTS.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; data access goes through the ULS index service
• Register new tools and resources via the barrels in src/mcp-server/*/definitions/index.ts
• The index is the source of truth at runtime — build and refresh it out-of-band, and keep blank ULS fields absent

Contributing

Issues are welcome. Run checks and tests before submitting:

bun run devcheck
bun run test

License

Apache-2.0 — see LICENSE for details.

License data comes from the FCC Universal Licensing System (ULS), a US government work in the public domain (17 U.S.C. §105). Credit it as "FCC Universal Licensing System (ULS)" with the dataAsOf time each response carries. This project redistributes none of the license data; operators download it from the FCC when building the index. The package does bundle a market-to-state table (src/services/uls/data/market-states.json) derived from FCC area definitions — the FCC's county-to-market file FCCCNTY2K.txt, its Partial Economic Area county list, and 47 CFR 80.385(a)(3) — which records only the states each market reaches. Basic Trading Areas delineated by the Rand McNally 1992 Commercial Atlas & Marketing Guide, 123rd Edition, at pages 38-39; extended and revised by the Federal Communications Commission, 59 FR 46195 (September 7, 1994). Major Trading Areas delineated by the Rand McNally 1992 Commercial Atlas & Marketing Guide, 123rd Edition, at pages 38-39, extended and excepted by the Federal Communications Commission, 59 FR 14115 (March 25, 1994). This server is independent of the FCC and not endorsed by it.