EVIDIQ Vault MCP

Autonomous AI agents make decisions, run tools, execute transactions, and update internal memory. Verifying what an agent did, in what order, under whose authority, and proving that logs were not altered after the fact is essential for agent governance.

EVIDIQ Vault is the governed, tamper-evident memory and audit trail layer for the agent economy. It records agent actions in append-only namespaces with SHA-256 hash chaining (prevHash linkage), seals range segments to 0G Storage via binary SHA-256 Merkle roots, enforces retention policies through tombstoning payload redaction, intercepts credential leaks, and issues signed audit reports.

Launch status: live endpoint, paid calls proven on-chain. The MCP server is deployed at https://mcp.evidiq.dev/vault/mcp and paid calls settle through the official OKX Payment SDK — see Proven on-chain. No OKX.AI listing has been submitted yet.

What it does

• Append-Only Hash Chaining — Every record is monotonically sequenced and cryptographically linked (prevHash points to prior recordHash).

• 0G Merkle Segment Sealing — Compute binary SHA-256 Merkle roots over record ranges and seal to 0G Storage.

• Retention & Tombstoning — Redact raw payload contents while preserving contentDigest and recordHash, ensuring chain continuity checks pass (INTACT).

• Credential & Secret Interception — Automatic pattern detection rejects private keys, mnemonics, and bearer tokens before they enter the vault.

• Continuity Audits — Evaluates namespace logs for INTACT, GAP, or BREAK verdicts with detailed policy violation tracking.

• Merkle Inclusion Proofs — Generate and verify Merkle inclusion proofs for individual records within sealed segments.

• Verifiable Reports — EIP-191 signed SHA-256 report digests.

• Pay Per Operation — Five paid tools cost 0.005–0.03 USDT0; five discovery and validation tools are free.

Related MCP server: kevros-mcp

Route to Vault when

Use Vault when an agent needs to record actions or decisions in governed memory, audit namespace continuity, seal record segments to 0G Storage, enforce payload retention, verify Merkle inclusion proofs, or generate signed audit reports.

Do not route dependency or package provenance to Vault (use EVIDIQ Lineage), and do not route endpoint or Agent Skill security scanning here (use EVIDIQ Sentinel). Vault records and proves what an agent did; it does not judge the safety of what it is about to use.

Use it from any agent

# Read the public Skill document
curl -s https://mcp.evidiq.dev/vault/skill.md

# Inspect current x402 pricing discovery
curl -s https://mcp.evidiq.dev/vault/x402

# Connect the remote MCP server (Claude Code)
claude mcp add --transport http evidiq-vault https://mcp.evidiq.dev/vault/mcp

Public endpoints:

MCP tools

Paid memory & audit operations

Free preflight and verification

Recommended workflow

Settlement happens before a paid tool runs, so a malformed argument is still a paid call. Preflight for free first:

1. vault_capabilities — current limits, secret-scanning rules, and prices.

2. validate_record — confirm the record's schema and that it carries no secrets. Note contentDigest must be bare 64-char SHA-256 hex; a 0x prefix is rejected.

3. estimate_cost — the exact price of the operation you intend to run.

4. One paid call per request.

5. get_receipt / verify_chain — free re-read and independent verification afterwards.

Engine limits

How a Vault append works

1. The record input is validated against the schema and scanned for secrets; a detected credential is rejected before storage.

2. A paid tool clears the x402 v2 payment gate before execution begins.

3. The namespace's current head is read to obtain the previous recordHash.

4. The record is canonicalized and hashed; prevHash links it to its predecessor.

5. The record is appended durably under a monotonically increasing seq.

6. A receipt envelope is returned with a SHA-256 integrity digest and an EIP-191 signature.

7. seal_segment can later fix a range of records under a Merkle root anchored to 0G Storage.

Record and receipt integrity

A paid append_record response contains:

• record — seq, namespace, actor, authority, action, tool, contentDigest, payload, tags, prevHash, and recordHash.

• recordId — the content-addressed record hash.

• integrity — SHA-256 digest over the canonical envelope, plus the EIP-191 signature and signer.

{
  "engine": "EVIDIQ-Vault/1.0",
  "chainFormatVersion": "v1",
  "data": {
    "record": {
      "seq": 1,
      "namespace": "evidiq-sdk-proof",
      "actor": "0xd6B658dC6e53444bF9Cba598aFdd21Ede0A62Fb9",
      "authority": "operator",
      "action": "verify",
      "contentDigest": "18b7a227d4c939603fb44112e78be92e434e46cd6abf0ecd92e56e45746cd28d",
      "prevHash": "0000000000000000000000000000000000000000000000000000000000000000",
      "recordHash": "e81012620100231edcc2488d0571dc0586322e1fc0f95be0cc795b8b5e8aa5ac"
    }
  },
  "integrity": { "algorithm": "SHA-256", "digest": "…" }
}

verify_chain recomputes each recordHash and checks the prevHash linkage, so a tampered or reordered log is detectable without trusting Vault. enforce_retention deliberately keeps contentDigest and recordHash when it redacts a payload, which is why continuity still verifies as INTACT after redaction.

Pricing and x402

Asset: USDT0 (6 decimals) on X Layer (eip155:196), contract 0x779ded0c9e1022225f8e0630b35a9b54be713736.

Official OKX Payment SDK

Payment verification and settlement run through the official OKX Onchain OS Payment SDK:

The OKX facilitator verifies each authorization and settles it on X Layer; Vault keeps ownership of the chain format, record signing, Merkle sealing, and retention policy. Each immutable per-tool price reaches the SDK as an explicit USD₮0 atomic asset amount rather than a USD string, so neither the fee nor its token can be substituted by currency conversion.

When the facilitator's own confirmation wait elapses it answers timeout even though the transaction it broadcast can still confirm moments later, so Vault resolves that state through the facilitator's settlement-status lookup rather than discarding a paid call. Success is only ever reported when the facilitator confirms it.

Integration guide: OKX Onchain OS — integrate via SDK.

Proven on-chain

Live paid calls against the deployed endpoint completed the full x402 v2 round trip through the official OKX facilitator:

Flow for both: unpaid call → HTTP 402 + PAYMENT-REQUIRED → EIP-3009 signature → PAYMENT-SIGNATURE retry → HTTP 200 + PAYMENT-RESPONSE (status: settled). Both receipts are status 0x1 on X Layer, and both were broadcast by an OKX facilitator relayer rather than by a Vault-held key — the on-chain evidence that settlement really ran through the official SDK. The appended record was afterwards re-read with the free get_receipt, so the paid write is durable and not merely acknowledged.

Free tools stay ungated and answer 200 without any payment header.

Architecture

flowchart TB
    agent["<b>AI agent</b><br/>MCP client"]
    request{"Tool call<br/>free or paid?"}
    agent -->|POST /vault/mcp| request

    free["Free preflight<br/>capabilities · validate<br/>estimate · verify_chain · get_receipt"]
    gate["x402 v2 gate<br/>EIP-3009 exact · pay per operation"]
    xlayer[("X Layer<br/>USD₮0 · eip155:196")]
    request -->|free helper| free
    request -->|paid operation| gate
    gate -. verify and settle .-> xlayer

    subgraph vault["EVIDIQ Vault trust boundary"]
        direction TB
        guard["1. Schema + secret guard<br/>keys · mnemonics · bearer tokens"]
        chain["2. Append-only chain<br/>SHA-256 prevHash linkage"]
        store["3. Durable namespace store<br/>monotonic seq"]
        seal["4. Merkle segment sealing<br/>binary SHA-256 root"]
        receipt["5. Signed receipt<br/>SHA-256 digest · EIP-191"]
        guard --> chain --> store --> seal --> receipt
    end

    zerog[("0G Storage<br/>sealed segment anchor")]
    seal -. anchor .-> zerog

    free --> guard
    gate --> guard

    response["<b>MCP response</b><br/>record + receipt + proofs"]
    receipt --> response

    classDef client fill:#312e81,stroke:#a78bfa,color:#ffffff,stroke-width:2px;
    classDef payment fill:#052e16,stroke:#4ade80,color:#ffffff,stroke-width:2px;
    classDef core fill:#0f172a,stroke:#38bdf8,color:#ffffff,stroke-width:2px;
    classDef output fill:#4c1d95,stroke:#c4b5fd,color:#ffffff,stroke-width:2px;
    class agent,request client;
    class free,gate,xlayer payment;
    class guard,chain,store,seal,receipt core;
    class response,zerog output;
    style vault fill:#0f172a,stroke:#38bdf8,color:#e0f2fe,stroke-width:2px;

Security boundaries

• Vault stores caller-supplied records; it never executes caller code and makes no outbound calls on behalf of a record.

• Secret patterns (private keys, mnemonics, bearer tokens) are rejected before a record is written, so the ledger cannot become a credential store.

• Records are canonicalized before hashing, so integrity checks are reproducible across platforms.

• Retention redacts payloads without rewriting hashes, so redaction can never be used to hide a tampered chain.

• EIP-191 signatures prove authenticity and non-repudiation of the attester key.

• The ledger directory is a bind mount owned by the unprivileged container user; the deploy script enforces that ownership on every release.

Self-host

Requirements: Node.js 22+ and npm.

npm install
npm run build
npm start

Or run the container:

docker build -t evidiq-vault .
docker run -d --name evidiq-vault -p 3000:3000 \
  --env-file .env -v evidiq-vault-data:/app/data/vault evidiq-vault

Local routes: POST /mcp · GET /skill.md · GET /x402 · GET /health

The ledger lives under VAULT_DATA_DIR (/app/data/vault by default). It must be writable by the container's vault user (uid 10001) — deploy/run.sh does this for you. A root-owned bind mount fails with EACCES on the first append.

Configuration

Copy .env.example to .env and set parameters:

# Server
PORT=3000
HOSTNAME=0.0.0.0
PUBLIC_BASE_URL=https://mcp.evidiq.dev/vault

# Official OKX Payment SDK — all three credentials are required together
OKX_API_KEY=...
OKX_SECRET_KEY=...
OKX_PASSPHRASE=...
OKX_BASE_URL=https://web3.okx.com

# x402 v2 — X Layer mainnet / USDT0 (prices are fixed per tool; no X402_PRICE)
X402_CHAIN=eip155:196
X402_ASSET=0x779ded0c9e1022225f8e0630b35a9b54be713736
X402_PAY_TO=0x2a8efe3093278bb4bd3b2d9c7b5ba992ca4fc9b0
X402_DOMAIN_NAME=USD₮0
X402_DOMAIN_VERSION=1
X402_RPC=https://rpc.xlayer.tech

# Record + segment signing (EIP-191)
VAULT_SIGNER_PRIVATE_KEY=...
VAULT_SIGNER_ADDRESS=0x...

# Durable chain storage
VAULT_DATA_DIR=/app/data/vault

# 0G Storage anchoring for sealed segments
OG_PRIVATE_KEY=...
OG_STORAGE_RPC=https://evmrpc.0g.ai
OG_STORAGE_INDEXER=https://indexer-storage-turbo.0g.ai

Development

npm install      # install dependencies
npm run build    # compile TypeScript to dist/
npm test         # run the 25-test suite (7 files)
npm run dev      # start local watch server

Links

• Website — https://evidiq.dev

• Vault documentation — https://evidiq.dev/docs/vault

• Live MCP endpoint — https://mcp.evidiq.dev/vault/mcp

• Agent Skill — https://mcp.evidiq.dev/vault/skill.md

• x402 discovery — https://mcp.evidiq.dev/vault/x402

• Service health — https://mcp.evidiq.dev/vault/health

• OKX Payment SDK guide — https://web3.okx.com/onchainos/dev-docs/payments/service-seller-sdk

• Settlement proof — https://www.oklink.com/xlayer/tx/0x7e96398e1f2bae0637af884b55b35cbc82099b8241858a1fdde3ab67c94db4b6

• EVIDIQ main repository — https://github.com/evidiq/evidiq

• x402 Protocol — https://x402.org

License

MIT © 2026 EVIDIQ — see LICENSE. Part of the EVIDIQ trust and execution layer for the AI agent economy.