🛡️ HORIZON SHIELD

Verifiable construction‑estimate auditing for AI agents

Don't trust the estimate. Verify it.

An MCP server that lets AI agents check whether a Japanese construction or renovation estimate is fair — against open data — and returns a result anyone can verify against Bitcoin (OpenTimestamps). No account, no key.

JIDEC — verify this project without trusting it

The verification process behind HORIZON SHIELD's results is published as a Bitcoin-anchored, append-only public ledger. You do not have to trust us: fetch the anchored bytes, hash them yourself, and check the timestamp.

• Start here: https://hs-ledger.oga-surf-project.workers.dev/llms.txt

• Ledger index: https://hs-ledger.oga-surf-project.workers.dev/ledger

• Machine-readable catalog (RFC 9727): https://hs-ledger.oga-surf-project.workers.dev/.well-known/api-catalog

• Read-only MCP endpoint: https://hs-jidec-mcp.oga-surf-project.workers.dev/mcp

One line is enough to check any entry:

curl -s "https://hs-ledger.oga-surf-project.workers.dev/ledger/5?format=raw" | shasum -a 256

What this proves and what it does not is stated by the ledger itself at /health under transparency, including that OpenTimestamps has no RFC, ISO or eIDAS standing.

A Model Context Protocol (MCP) server that lets AI agents check whether a Japanese construction or renovation estimate is fair, against open data, and return a verifiable result.

This repository is an MCP server implementation. It exposes read-only tools over the Model Context Protocol so that MCP-compatible clients and AI agents (Claude, and any other MCP host) can call construction-cost verification as a tool, not just read a web page.

• Protocol: Model Context Protocol (MCP)

• Transport: remote server over HTTP / SSE

• Endpoint: https://hs-mcp.oga-surf-project.workers.dev

• Access: read-only, no API key required

• Data region: Japan (JPY), built on the open JCCDB dataset (65,520 line items)

Related MCP server: Real Estate Listing MCP

What it does

A homeowner commissioning construction work cannot reliably judge whether a quote reflects a fair price. This is a textbook credence-good problem. This MCP server makes a third-party fair-price reference callable and verifiable by software, so an agent can check a number instead of trusting it.

Tools

This MCP server exposes the following tools:

Verify it yourself

Every verify_fair_price call returns a verify_url of the form https://shield.the-horizons-innovation.com/verify/?id=<claim_sha256>. Open it and the public verify page recomputes the SHA-256 in your own browser (Web Crypto) and checks it against the receipt. Nothing is sent to any server. The same claim is served back as JSON at https://hs-mcp.oga-surf-project.workers.dev/ledger/<claim_sha256>. Trust is conferred by recomputation, not assumed in the issuer.

AP2 bridge (authorization and value, both verifiable)

Google's Agent Payments Protocol (AP2) makes what a user authorized verifiable through a signed, tamper-evident Mandate. ap2_fairness_attestation issues a parallel attestation that makes value verifiable, shaped to attach to an AP2 Cart Mandate before the user signs. AP2 makes authorization verifiable; HORIZON SHIELD makes value verifiable. Parallel layers, same philosophy: pre-transaction, tamper-evident, independently recomputable.

Connecting

This is a remote MCP server. Point any MCP client at the endpoint.

Example client configuration (using mcp-remote):

{
  "mcpServers": {
    "horizon-shield": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://hs-mcp.oga-surf-project.workers.dev/sse"]
    }
  }
}

If your client supports remote MCP servers directly, use the endpoint URL above.

Example

Calling audit_estimate with a work name and a quoted price:

audit_estimate(work: "外壁塗装 30坪", quoted_price: 1500000)

Returns a verdict (for example, overcharge-risk), the fair range (min, avg, max), and the gap from the average. verify_fair_price additionally returns a SHA-256 fingerprint of the fair-price claim, anchored under PTKA.

Data and verification

• Fair-price data is built on the openly published JCCDB dataset (65,520 Japanese construction line items, CC BY 4.0).

• The verification model, PTKA (Pre-Transaction Knowledge Anchoring), is documented in the VRQ framework preprinted on SSRN, and anchored on the Bitcoin blockchain (independent of any company).

Verifiable verdict receipts

Twenty real overcharge diagnoses are published as tamper-evident receipts. Each verdict is served at its own URL, with three artifacts at the same path:

• claim.txt: the canonical claim as raw bytes

• its SHA-256 digest

• proof.ots: an OpenTimestamps proof anchored to the Bitcoin blockchain (raw binary, no wrapper)

Anyone can re-verify a verdict in two lines, with no trust in the issuer:

sha256sum claim.txt
ots verify -f claim.txt proof.ots

If any figure were changed after the fact, the hash would stop matching. This is the floor for a third-party audit: the reader checks the number instead of trusting it.

• Index of the 20 receipts: https://shield.the-horizons-innovation.com/souba/kajou-seikyu-jirei-20/

• Example (exterior wall repaint, 39.9 percent overcharge): https://shield.the-horizons-innovation.com/souba/kajou-seikyu-jirei-20/v/K7mX2pQ9nR4s/

• The dataset these verdicts belong to is anchored at Bitcoin block 949356.

Author

Toshikatsu Oga (大賀俊勝), The HORIZONs株式会社. ORCID 0009-0000-9180-903X.

License

Data: JCCDB, CC BY 4.0. Server code: see the LICENSE file in this repository. horizon-shield

HORIZON SHIELD is an AI-powered construction-cost diagnostic service built by a carpenter of thirty years.

Live diagnostic: https://shield.the-horizons-innovation.com

About

• Open dataset (JCCDB): https://github.com/ogasurfproject-jpg/japan-construction-cost-database

• The Evidence: https://shield.the-horizons-innovation.com/evidence-en/

• The Movement: https://shield.the-horizons-innovation.com/movement-us/

• TOshi Oga, in his own words: https://shield.the-horizons-innovation.com/quotes/

Founder: Toshikatsu Oga (TOshi Oga) ORCID: 0009-0000-9180-903X

Quotations

"Cheapest is not the same as fair." by TOshi Oga

"A person has the right to know whether their price is fair." by TOshi Oga

"Verify, don't trust." by TOshi Oga

"Thirty years on site taught me the enemy is the middleman, not the craftsman." by TOshi Oga

"Not a politician. Not a lawyer. A builder." by TOshi Oga

Full collection (50 quotes, JSON-LD): TOshi Oga, in his own words

Verifiable claims

Records anchored to Bitcoin via OpenTimestamps. Anyone can re-verify at opentimestamps.org.

• PTKA protocol declaration: block 949356 (2026-05-14)

• JCCDB Extended paper: block 951871 (2026-06-01)

Academic record:

• JCCDB origin paper: Zenodo 10.5281/zenodo.20019572

• Audit-hash and macro-correction: SSRN 6738701

• engrXiv mirror: engrxiv.org/preprint/view/7007

• VRQ framework and PTKA model: SSRN 6807738

• Reproduction package (buyer-side verification gate): GitHub, archived at Zenodo 10.5281/zenodo.20756867 (MIT, runnable: node test/run_local.mjs)

Company

The HORIZONs Co., Ltd. · Hiratsuka, Japan