Overview

US radio spectrum licensing from the FCC Universal Licensing System (ULS), served from a local SQLite index of the FCC's weekly and daily bulk files. Look up a callsign, licensee, FCC Registration Number (FRN), or market code; read a license's sites, antennas, frequencies, power, and emission designators; find licensed transmitter sites near a point; and see who is authorized on a frequency or band, market-area spectrum blocks included. No API key, and no call to the FCC at request time. Runs as a stdio process, a local Streamable HTTP server, or the public hosted endpoint above.

The default index covers land mobile (private, commercial, and broadcast auxiliary), microwave, cellular, market-area wireless, paging, coast stations, broadband radio (BRS/EBS), and amateur licenses, plus spectrum leases. GMRS, ship, and aircraft licenses are opt-in. Broadcast stations (AM/FM/TV) and satellite earth stations are separate FCC systems and are not included.

Tools

Resources

Also reachable via fcc_spectrum_get_license.

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
• limit 1–100 (default 25) 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

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: up to 50 sites, 100 antennas, 100 leases, and max_frequencies frequency rows (1–1000, default 100) per call; nextLocationOffset and nextLeaseOffset feed location_offset and lease_offset on the next call
• location_number starts the locations at a site's locationNumber from fcc_spectrum_find_transmitters or fcc_spectrum_search_frequencies, or at the next filed number when the record has no such location; 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

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, limit 1–100 (default 25) with cursor paging; each site lists up to max_frequencies_per_site frequencies (1–50, default 10), with frequencyCount carrying the full count
• Each site carries locationTypeCode and locationTypeLabel when a type is filed, and radiusKm when a radius is; a mobile or temporary-fixed operating area is returned at its filed center, and distanceKm measures to that center
• Typed errors: invalid_frequency_range, unknown_radio_service, service_not_indexed, invalid_cursor, index_not_ready

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); limit 1–200 (default 50) with cursor paging, frequency ascending; each row's kind says whether it is a site assignment or a market block
• market_code and frn test the license, so they filter site rows and market rows alike: cellular CMA licenses file sites, not blocks. With state, both apply. An frn search returns individual licensees redacted
• A site row at a single site carries its locationTypeCode, locationTypeLabel, and, when filed, radiusKm; a row under a location number several sites share carries none of them, as it carries no coordinates
• Typed errors: invalid_frequency_range, unknown_radio_service, service_not_indexed, invalid_cursor, index_not_ready

fcc_spectrum_list_reference _tool

• topic: radio_services, license_statuses, location_types, antenna_types, applicant_types, operator_classes, or coverage; filter narrows radio_services to entries containing every word given
• 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

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

• The first page of fcc_spectrum_get_license (up to 100 frequency rows) 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
• Index generations — a weekly rebuild writes a new file beside the one being served, and the server switches to it within a minute; the daily refresh and a schema upgrade update the served file in place, each change in one transaction
• 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
• Absent stays absent — fields ULS leaves blank are omitted, and coordinates that fail validation are kept as DMS text (coordinatesDms)
• Discriminated output — found, kind, isLease, licenseeRedacted, and technicalRetained let callers branch on data, not string parsing

Getting started

Public Hosted Instance

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

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

The hosted index is rebuilt weekly and refreshed daily from the FCC bulk files, with individual licensees redacted.

Self-Hosted / Local

The index must be built once before any search works — see First-run setup. The package does not ship FCC data; until mirror:init has run, data tools fail with index_not_ready and fcc_spectrum_list_reference with topic coverage reports the build state.

Add the following to your MCP client configuration file:

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

Or with npx (no Bun required):

{
  "mcpServers": {
    "fcc-spectrum-mcp-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@cyanheads/fcc-spectrum-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info",
        "FCC_SPECTRUM_MIRROR_DIR": "/path/to/fcc-uls"
      }
    }
  }
}

Or with Docker (mount a volume at /usr/src/app/.mirror so the index persists across containers):

{
  "mcpServers": {
    "fcc-spectrum-mcp-server": {
      "type": "stdio",
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-e", "MCP_TRANSPORT_TYPE=stdio",
        "-v", "fcc-uls:/usr/src/app/.mirror",
        "ghcr.io/cyanheads/fcc-spectrum-mcp-server:latest"
      ]
    }
  }
}

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

MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 FCC_SPECTRUM_MIRROR_DIR=/path/to/fcc-uls bun run start:http
# Server listens at http://localhost:3010/mcp

FCC_SPECTRUM_MIRROR_DIR must name the directory mirror:init built. A relative path resolves against the process's working directory, which an MCP client chooses, so use an absolute path.

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 (see Installation) or 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

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). A daily refresh that has fallen more than six days behind runs the weekly rebuild instead. 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.

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 index (see First-run setup):

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

Configuration

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.

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), fcc_spectrum_search_frequencies stops each call short. A page can hold fewer rows than limit and still carry nextCursor, and totalCount is then a lower bound (totalIsLowerBound: true). A sparse filter across a wide band can return several empty pages before its first rows; a state, radio_service, licensee, frn, or market_code filter narrow enough keeps 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 codes pass through undecoded (FB2, FXO, MO).
• 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

Local development

• Build and run:

  sh

  # 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:

  sh

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

The image defaults to HTTP transport with stateless sessions, includes the mirror:* CLI, and logs to /var/log/fcc-spectrum-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/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.