Xyntherium Verify MCP

Let any AI agent verify an answer against its sources before it states a fact or takes an action.

Two tools, hosted at https://www.xyntherium.com/mcp (Streamable HTTP, bearer auth; use the www. address, the bare domain currently redirects and a redirect drops the key):

Tool	Input	What comes back
verify_answer	answer, sources[] ({ text, id?, title? }), question?, mode?	Every claim in the answer marked supported, unsupported or contradicted, with the source passage that decides it, and one verdict: send, cite_sources, revise or ask_a_person
verify_against_document	answer, document_text, title?, question?, mode?	The same, against one document

It catches a dropped condition ("within 30 days for unopened items"), a changed number or date, a flipped negation, a wrong entity, and any statement the sources never make. It checks only against the text you pass: it never fetches URLs and does not check facts about the world.

This repository is the integration layer: install snippets, example configs, a system-prompt snippet and a tiny client wrapper. The hosted service is closed source; the deterministic engine behind it is open at augustbrookz/verify-gate.

Install

Get an API key at https://xyntherium.com/account/api-keys (free: 1,000 checks a month, 50 a day over MCP, no card).

Claude Code

claude mcp add --transport http xyntherium-verify https://www.xyntherium.com/mcp \
  --header "Authorization: Bearer $XYN_API_KEY"

Add --scope user to make it available in every project. claude mcp list shows it connected.

Claude Desktop

Settings → Developer → Edit config (claude_desktop_config.json), through the mcp-remote bridge (examples/claude_desktop_config.json):

{
  "mcpServers": {
    "xyntherium-verify": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://www.xyntherium.com/mcp", "--header", "Authorization: Bearer ${XYN_API_KEY}"],
      "env": { "XYN_API_KEY": "xyn_live_…" }
    }
  }
}

Or Settings → Connectors → Add custom connector with https://www.xyntherium.com/mcp and no key: Claude sends you to Xyntherium to sign in and approve access (OAuth, 90 days).

Cursor

~/.cursor/mcp.json or .cursor/mcp.json (examples/cursor-mcp.json):

{
  "mcpServers": {
    "xyntherium-verify": {
      "url": "https://www.xyntherium.com/mcp",
      "headers": { "Authorization": "Bearer xyn_live_…" }
    }
  }
}

VS Code

.vscode/mcp.json (examples/vscode-mcp.json); VS Code asks for the key once and stores it securely.

Any other MCP client

URL https://www.xyntherium.com/mcp, header Authorization: Bearer <key>, Streamable HTTP, stateless, protocol 2026-07-28 and 2025-11-25 (and 2025-06-18 / 2025-03-26 through initialize). Discovery and tools/list need no key; every tool call does.

30-second demo

1. Install with the Claude Code command above.

2. Ask Claude:

   Our return policy says: "Refunds are available within 30 days for unopened items with proof of purchase."
   A customer asks if they can get a refund. Draft a one-sentence reply, then verify it with
   xyntherium-verify before you show it to me, and fix anything the check flags.
   

3. Claude drafts "Yes, refunds are available within 30 days", calls verify_against_document, and gets:

   REVISE: dropped “for unopened items with proof of purchase”.
   - Dropped: “Refunds are available within 30 days.” leaves out “for unopened items with proof of purchase”; the source says “within 30 days for unopened items with proof of purchase” (source document).
   Claims:
   1. [unsupported] “Refunds are available within 30 days.”; drops “for unopened items with proof of purchase”; source document: “Refunds are available within 30 days for unopened items with proof of purchase.”.
   0 of 1 statements supported · mode fast · rules 2.1.0 · request …
   

4. Claude rewrites the reply with the conditions, checks again, and gets SEND.

From a shell, without any client:

curl -s -X POST https://www.xyntherium.com/mcp \
  -H "Authorization: Bearer $XYN_API_KEY" \
  -H 'content-type: application/json' -H 'accept: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"verify_against_document","arguments":{
    "answer":"Refunds are available within 30 days.",
    "document_text":"Refunds are available within 30 days for unopened items with proof of purchase."}}}'

Telling your agent when to call it

The server sends every client these instructions; examples/agent-system-prompt.md has a longer version for your own system prompt:

Before you state facts drawn from documents in the conversation, or act on them (send a reply, file a change, book, refund, approve), verify the drafted answer: call verify_answer with the answer and the passages it relies on, or verify_against_document with the answer and the one document it rests on. On REVISE, fix what it names and check again before proceeding. On ASK A PERSON, tell the user what the sources do not settle instead of guessing. Do not call it for chit-chat, for answers with no source text, or to fact-check the world.

The result

Text (the verdict first, then each problem, then every claim) and the same as structuredContent:

以上为 README 的开头部分。其余内容请阅读原文。 查看完整 README ↗