# x402 Reverse Geocoder — Lat/Lng to US Census Block

> x402 Reverse Geocoder — Lat/Lng to US Census Block is a paid API for AI agents from x402-geocoder-production.up.railway.app, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-15).

Reverse-geocodes a decimal latitude/longitude coordinate to its enclosing US Census block, returning state, county, tract, and block FIPS codes.

## Facts

- Endpoint: POST https://x402-geocoder-production.up.railway.app/geocode/reverse
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-geocoder-production-up-railway-app-a4f6ca39
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_9XjCRVyoFW7FMRh2iJnnT

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability x402-geocoder-production-up-railway-app-a4f6ca39 -d '<json body>'
```

Example prompt: What US Census block, tract, county, and state FIPS codes correspond to the coordinates latitude 38.8977 and longitude -77.0365?

## When to prefer this

Use this endpoint when you need to identify the precise US Census geographic unit (block/tract/county/state) for a known lat/lng coordinate — for example, to join demographic data, comply with census-based reporting, or resolve a GPS point to an administrative geography. Prefer this over forward geocoding when you already have coordinates and need FIPS codes rather than a street address.

## Known failure modes

- Coordinates outside the US return no result or an error (US-only coverage)
- Invalid or missing lat/lng parameters return a 400-level error
- Coordinates in US waters or uninhabited areas may not map to a census block
- Payment charged per call regardless of whether a result is found

## How this service works

Reverse-geocode a lat/lng coordinate to its enclosing US Census block (state/county/tract/block FIPS codes). Query params: lat (required, decimal degrees), lng (required, decimal degrees). US-only coverage.

## Output

Returns the US Census FIPS codes for the state, county, census tract, and census block that contain the given lat/lng point. Coverage is US-only.

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-geocoder-production-up-railway-app-a4f6ca39/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402-geocoder-production.up.railway.app](https://www.zero.xyz/host/x402-geocoder-production.up.railway.app/llms.txt)