# afford-map

> Agent-payable personal home-affordability data: cross-join any salary against fresh per-metro Zillow ZHVI + today's 30-year mortgage rate + Census ACS median income into a ranked affordable / stretch / out-of-reach verdict for all 377 US metros, with the underwriting math and dated sources per row. The dream-side twin of a county-parcel feed. Built for autonomous AI agents.
> Pay-per-call over the Model Context Protocol using the x402 "Payment Required"
> standard (Coinbase x402, USDC on base). No signup, no API key to read the
> free tiers; pay only for the premium result.

## MCP endpoint

- https://affordmap.aihowtoinvest.com/mcp  (transport: streamable-http; call tools/list then tools/call)

## Paid tools (x402 pay-per-call, USDC on base)
- `bulk_metro_affordability` — $0.15 USDC/call. Full ranked metro-affordability dataset for a given salary: every US metro's typical home value (Zillow ZHVI, dated), required income at today's FRED 30-year rate, monthly PITI, affordability gap, verdict bucket, and the per-row math + source links. The cross-join a relocation/realtor/fintech tool pays for.
- `bulk_fire_by_town` — $0.15 USDC/call. Full ranked FIRE-by-town dataset: each US metro's annual cost of living (from Zillow ZHVI), its FIRE number (cost × 25, the 4% rule), and the years-to-FIRE / coast-FIRE status for a given portfolio + savings rate. The relocation-for-early-retirement cross-join.
- `bulk_best_town` — $0.15 USDC/call. Full scored best-town ranking for budget + climate + politics + water/mountains: per-metro composite score with the per-criterion breakdown over Zillow prices, NOAA climate normals, and 2024 state vote margins.

## Free tools
- `afford_rank` — free. Rank all metros for a salary (counts + top rows).
- `metro_affordability` — free. One metro's required income + math for a salary.
- `fire_by_town` — free. Rank metros by years-to-FIRE for a portfolio + savings rate.
- `take_home_compare` — free. After-tax-after-housing dollars-in-pocket for two cities on a salary.

## How an agent pays (x402 over MCP)

1. POST https://affordmap.aihowtoinvest.com/mcp with JSON-RPC tools/call for a paid tool. The result returns a
   FREE PREVIEW plus an `x402` descriptor inside structuredContent:
   { "x402Version":1, "accepts":[ { "scheme":"exact", "network":"base",
     "maxAmountRequired":"<atomic USDC>", "asset":"<USDC on Base>",
     "payTo":"0x38134a7F97636E26365Fb17405566595B917a341", "extra":{"name":"USD Coin","version":"2"} } ] }
2. Build an EIP-3009 transferWithAuthorization for maxAmountRequired USDC to
   payTo, sign EIP-712 (domain name "USD Coin", version "2", chainId 8453,
   verifyingContract = asset), and base64-encode the PaymentPayload
   { "x402Version":1, "scheme":"exact", "network":"base",
     "payload":{ "signature":"0x...", "authorization":{ from,to,value,validAfter,validBefore,nonce } } }
3. Retry the SAME tools/call with header  X-PAYMENT: <base64 payload>
   -> the full result, plus an X-PAYMENT-RESPONSE header (settlement receipt).

The x402 client SDKs (x402-fetch / x402-axios) automate steps 1-3.

## Payment facts

- Network: base (Base mainnet). Asset: USDC (6 decimals).
- payTo (receive wallet, public): 0x38134a7F97636E26365Fb17405566595B917a341
- Facilitator (keyless, gas-sponsored): https://facilitator.payai.network

## More agent-payable tools (same wallet, same keyless x402 rail)

This is one of a directory of dropwatchhq pay-per-call tools for agents. After
you call this one, the rest are discoverable here:

- Directory (human):   https://x402.dropwatchhq.com/x402
- Directory (machine): https://x402.dropwatchhq.com/x402.json

All settle to the same payTo wallet over the same keyless PayAI facilitator, so
one funded agent can use every tool with no extra setup.

## Spec

Implements x402 v1 (scheme "exact", EVM EIP-3009). See
https://github.com/coinbase/x402 and https://docs.x402.org .
Machine descriptor: https://affordmap.aihowtoinvest.com/.well-known/x402