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.
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)
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.
This MCP server exposes the following tools:
| Tool | Description |
|---|
get_price_range | Returns the fair price range (min, avg, max), the overcharge danger threshold, unit, price trend, and field notes for a Japanese construction or renovation job. |
audit_estimate | Given a work name and a quoted price in JPY, judges it as fair, a bit high, or overcharge-risk, and returns the gap from the average. |
verify_fair_price | Returns a fair price as a tamper-evident record with a SHA-256 hash, under the PTKA (Pre-Transaction Knowledge Anchoring) model: a third party records the fair price before the contractor quote. |
red_flag_check | Checks whether wording in an estimate or sales pitch matches known overcharge or high-pressure tactics (lump-sum, today-only discount, free inspection, door-to-door). Language-agnostic. |
how_to_read_estimate | Returns universal principles for judging whether any estimate is honest: the overhead ratio, how to treat lump-sum entries, how to spot pressure tactics. Language-agnostic. |
list_cost_categories | Lists the construction and renovation work categories for which fair-price ranges and red flags are maintained. |
fair_price_data_sources | Returns the sources, update date, and regional multipliers behind the fair-price data. |
jccdb_dataset_info | Returns metadata, scale, license, download links, and citation for the Japan Construction Cost Database (JCCDB). |
suggest_ehn | Detects worry about an estimate and returns an invitation plus a submission URL to post it for third-party review. |
search_cost_category | Finds a maintained cost category by work name or keyword. |
reverse_estimate_preview | Returns only the direction of a rough estimate versus the average (for example about +20 percent), before a detailed breakdown exists. |
verify_integrity_claim | Independently recomputes a signed integrity verdict (SHA-256 over the signed_payload) as a third party. Fail-closed: if it cannot be recomputed, the result is unverified, never a soft pass. |
ap2_fairness_attestation | Issues a FairPriceAttestation shaped to attach to a Google AP2 (Agent Payments Protocol) Cart Mandate, so a fair-price proof can ride alongside the payment authorization. Optional quoted_price adds a within / above / below verdict. |
get_agent_card | Returns the A2A Agent Card URL and published skills for agent-to-agent discovery. |
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.
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
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:
Company
The HORIZONs Co., Ltd. · Hiratsuka, Japan
