SkyGlance

Quick Start

claude mcp add skyglance -- uvx --from skyglance skyglance

Then ask Claude: "What's flying over me right now?"

Needs uv (curl -LsSf https://astral.sh/uv/install.sh | sh). No API keys — every data source here is free.

Set your location so you can stop repeating it, and so SkyGlance can build a sighting history:

claude mcp add skyglance \
  -e SKYGLANCE_HOME_LAT=40.71 -e SKYGLANCE_HOME_LON=-74.01 \
  -- uvx --from skyglance skyglance

Install as a Claude Code plugin

Ships the server together with the sky skill, which teaches Claude how to read elevation angles and how to talk about aircraft to someone who has never spotted one.

/plugin marketplace add darshjoshi/skyglance-mcp
/plugin install skyglance@skyglance

Related MCP server: adsb-mcp-server

What you can ask

"What's flying over me right now?"         → ranked by what you'd actually notice
"What's about to pass overhead?"           → but only 90 seconds ahead, honestly
"What is that plane?"                      → type, operator, route, photograph
"Where is flight UAL123?"                  → anywhere in the world
"Any A380s airborne?"                      → 44 of them, right now
"Any military aircraft near me?"           → and any emergencies, worldwide
"Have I ever seen this plane before?"      → your own history says
"What's the closest one ever?"             → your personal records
"Can I even see anything tonight?"         → cloud, visibility, daylight

Why it's shaped this way

"Over you" is an angle, not a distance. A radius filter returns an airliner at 38,000 ft that is 19 km away — sitting 32° above the horizon, a speck near the treeline — and gives it the same weight as a helicopter at 800 ft, at 0.7°, invisible behind buildings. SkyGlance computes the elevation angle, the compass bearing to look, and the slant range, so an answer tells you where to point your face.

It won't predict further than it can. Straight-line extrapolation from track and ground speed is accurate to about 0.11 km at 30 seconds. At four minutes the median miss is 6 km and 77% of aircraft are more than 2 km off, because aircraft on approach turn constantly. So countdowns stop at 90 seconds and anything beyond is reported as "inbound" with no number attached.

It knows when it can't see. Free ADS-B coverage comes from volunteers with receivers on their roofs. Dense Europe, US and East Asia get 90–95% of what a commercial feed shows. Oceans, Africa and central Asia get near zero. When results are thin, SkyGlance says so rather than implying an empty sky.

Your coordinates are rounded before they leave. Feed queries are coarsened to two decimal places (~1.1 km) so no volunteer feed operator gets a rooftop-accurate log of where you are and when you're awake. Bearing and elevation are still computed locally from your exact position, so what you're told to look at stays precise. There's a test that fails if an uncoarsened coordinate ever reaches a feed.

The 24 tools

How this compares to Flightradar24

SkyGlance is a question-answering tool, not a map, so the comparison is about what you can find out rather than what you can look at.

The honest summary: for spotting and identification — what's above me, what is that, where has it been, how many 747s are up — SkyGlance covers what FR24 charges Silver and Business for, at $0. For travel logistics — is my flight delayed, what gate — it cannot compete, because that's licensed schedule data rather than ADS-B. And FR24's satellite network sees oceanic traffic that volunteer receivers simply cannot hear.

So: a strong replacement for the enthusiast half, not for the passenger half.

What it deliberately can't do

Free ADS-B carries positions, not schedules. So there are no delays, no ETAs against a timetable, no gates or terminals, and no way to search "flights from JFK to London today" — route lookup only runs the other way, from a callsign you already have. track_history is a rolling ~24-hour window, not an archive.

These aren't on a roadmap. They're a different data product (Cirium, OAG, FlightAware), and buying one would end the no-API-keys story. The tools refuse these questions explicitly rather than estimating, and the bundled skill tells Claude to do the same.

Sighting history

With SKYGLANCE_HOME_LAT/LON set, SkyGlance polls your sky once a minute in the background and records every pass. That's what makes the questions no live feed can answer possible: have I seen this tail before, is this type new here, what's the lowest anything has ever come over.

• Stored locally in SQLite at ~/.skyglance/sky.db. Nothing is uploaded anywhere.

• Only one process polls, even with several Claude sessions open — a pid-stamped lock enforces it, so volunteer feeds don't get hit N times over.

• Turn it off with SKYGLANCE_POLL=0.

• Honest limit: passes are inferred from snapshots a minute apart, so a fast low pass between polls isn't recorded. poller_status tells you the interval.

Configuration

Where the data comes from

Eight free services, no API keys, $0/month. Full terms in NOTICE.md.

All three position feeds are queried in parallel and merged, not failed over. Measured over Newark on 2026-08-02: 52 aircraft from the best single source, 61 from the union — 17% more. Merging buys coverage as well as redundancy.

Each source sits behind a circuit breaker (three strikes, 30-second cooldown). These are volunteers paying for their own bandwidth, with no SLA and no obligation to anyone. If all three fail, the last good snapshot is served flagged stale rather than an error — a 40-second-old aircraft beats a spinner.

Not suitable for anything operational. Dispatch, safety, ATC-adjacent — buy a commercial feed. The upstream terms say the same.

Related

• skyglance-mac — the same data as a macOS menu bar app, with the research this is built on (FREE-STACK.md, OVERHEAD-DETECTION.md, COVERAGE-AND-COST.md)

Development

uv venv && uv pip install -e ".[dev]"
pytest                    # geometry parity, merge, breakers, privacy, history

The geometry tests assert exact-digit parity with reference/overhead.mjs from the Mac app, which passes its own 11 known-answer cases. If the port ever drifts, those fail first.

MIT licensed. Not affiliated with any airline, airport, or air navigation service provider.