# fact-check **Category:** ๐Ÿ’ป Developer Tools **Repository:** https://github.com/lenzhq/lenz-mcp **Views:** 0 **Installs:** 0 **Upvotes:** 0 **Directory Page:** https://allmcps.com/mcp/fact-check ## Description Fact-check claims against independent sources โ€” fast verdict or deep multi-step investigation. ## Claude Desktop Quick Installation Heuristic fallback โ€” verify the package name and runner against the repository README before running it. Uses `npx` (confidence: low): ```json "mcpServers": { "fact-check": { "command": "npx", "args": ["-y","fact-check"] } } ``` ## Documentation & README

Lenz

Lenz MCP Server

Fact-check claims against independent sources โ€” from any MCP client.

Website ยท Get an API key ยท Developer docs

Add Lenz to Cursor   Install Lenz in VS Code

One-click install (OAuth โ€” no API key needed).

--- [Lenz](https://lenz.io) is a fact-checking platform. It takes a factual claim, runs it through a multi-model pipeline (framing โ†’ research โ†’ debate โ†’ panel review โ†’ conclusion) against independent sources, and returns a verdict with a confidence level. This is the official **remote MCP server** โ€” a hosted [Model Context Protocol](https://modelcontextprotocol.io) endpoint that exposes Lenz's fact-checking as tools your AI assistant can call. It verifies claims **against the open web**, independent of whatever context your model was given โ€” so it complements retrieval/groundedness checkers rather than replacing them. - **Hosted, no install:** point your client at `https://lenz.io/mcp`. Nothing to run locally. - **Auth:** **OAuth** (no key โ€” for clients that support it) or a free Lenz **API key** (`Authorization: Bearer lenz_โ€ฆ`). - **Transport:** Streamable HTTP. ## Tools | Tool | What it does | |------|--------------| | **`assess_claim`** | Fast verdict (~10s) via a 3-model panel. The default for checking a claim. Returns one verdict per atomic claim (True / Mostly True / Mixed / Mostly False / False) plus bucketed confidence. | | **`verify_claim`** | Deep, multi-step investigation (~90s: research โ†’ debate โ†’ panel review) for high-stakes claims. Returns a `task_id` immediately; poll it with `get_verification`. Costs an order of magnitude more credits than `assess_claim` โ€” reserve it. Pass `depth: "low"` for a shallower, faster research pass (fewer sources, same models) at half the credits. | | **`get_verification`** | Retrieve or poll a `verify_claim` result by `task_id`. Returns `processing`, `needs_input`, or `completed` (verdict, summary, top sources, and the `depth` the verdict was produced at). | | **`select_claims`** | Resolve a `needs_input` verification โ€” when a `verify_claim` turns up multiple claims or an ambiguity, pick which claim text(s) to run. | | **`ask_followup`** | Ask a grounded follow-up about a completed `verify_claim` (by its `verification_id`) โ€” answered from the full research, debate, and panel review, not just the summary. Costs credits at the cheap rate, same as `assess_claim`. | | **`check_usage`** | Your remaining credits, the per-tool price list (`costs`, plus `cost_options` for prices that depend on a parameter such as `depth`), and your current plan. | > Verdicts are **directional, not absolute** โ€” confidence is returned as bucketed > language with a caveat, not a raw score. Surface it, and the link back to Lenz, to > the user. ## Quickstart Two ways to connect, depending on your client: - **OAuth** โ€” for clients that support it (e.g. Claude connectors). No key to paste; you sign in to Lenz and authorize the connection. - **API key** โ€” works with any MCP client via an `Authorization` header. ### Connect with OAuth (no API key) **Claude (web, desktop and mobile):** Lenz is an official Claude connector. Open the [Lenz connector page](https://claude.ai/directory/connectors/lenz) and click **Connect to Claude**, or in the app: **Settings โ†’ Extensions โ†’ Browse extensions**, search for Lenz and click **+**. Either way it is a one-time OAuth sign-in with nothing to configure, and one account covers all three. For any other client that supports OAuth for MCP, add the server with just its URL and no headers: ```json { "mcpServers": { "lenz": { "type": "http", "url": "https://lenz.io/mcp" } } } ``` The first time you use it, your client walks you through a one-time sign-in: you authenticate on Lenz's own screen and authorize the connection โ€” no key is stored in your config. Your assistant then fact-checks on your behalf against your Lenz account's credits. You can revoke the connection at any time; see the [privacy policy](https://lenz.io/privacy). ### Connect with an API key **1. Get a free API key** at [lenz.io/api-credentials](https://lenz.io/api-credentials) (format `lenz_โ€ฆ`). **2. Add the server** to your client (examples below). Authenticate with `Authorization: Bearer `. ### Claude Code ```bash claude mcp add --transport http lenz https://lenz.io/mcp \ --header "Authorization: Bearer ${LENZ_API_KEY}" ``` ### Claude Desktop / any client that reads `.mcp.json` ```json { "mcpServers": { "lenz": { "type": "http", "url": "https://lenz.io/mcp", "headers": { "Authorization": "Bearer ${LENZ_API_KEY}" } } } } ``` ### Cursor **One click:** use the [**Add Lenz to Cursor**](https://cursor.com/en/install-mcp?name=lenz&config=eyJ1cmwiOiJodHRwczovL2xlbnouaW8vbWNwIn0%3D) button above โ€” it adds the server and signs you in via OAuth (no key to paste). Manual: Settings โ†’ **MCP** โ†’ **Add new MCP server** โ†’ type **HTTP**, URL `https://lenz.io/mcp`, and add a header `Authorization: Bearer `. (Or drop the JSON above into `.cursor/mcp.json`.) ### VS Code **One click:** use the [**Install in VS Code**](https://vscode.dev/redirect/mcp/install?name=lenz&config=%7B%22type%22%3A%22http%22%2C%22url%22%3A%22https%3A%2F%2Flenz.io%2Fmcp%22%7D) button above (OAuth, no key). Manual, with a key: ```bash code --add-mcp '{"name":"lenz","type":"http","url":"https://lenz.io/mcp","headers":{"Authorization":"Bearer ${LENZ_API_KEY}"}}' ``` ### ChatGPT At this time, ChatGPT connects to Lenz as a custom app through OpenAI's **Developer mode** โ€” over OAuth, so there is no API key to paste. It is set up on chatgpt.com; the ChatGPT desktop and mobile apps cannot create one. **On a personal account (Plus or Pro).** **Settings โ†’ Plugins** โ†’ turn on **Developer mode** at the bottom โ†’ **Plugins โ†’ Browse plugins** โ†’ **+** next to Search โ†’ name it Lenz, URL `https://lenz.io/mcp`, Authentication **OAuth** โ†’ tick **I understand and want to continue** โ†’ **Create** โ†’ **Sign in with Lenz** โ†’ **Try in Chat**. **In a Business, Enterprise or Edu workspace.** An owner or admin publishes it once: **Workspace settings โ†’ Apps โ†’ + Create**, confirm **Enable developer mode**, fill in the same form with **OAuth**, then **Drafts โ†’ Publish**, set who can use it, and **Publish** again. Each member then goes to **Settings โ†’ Plugins โ†’ Lenz โ†’ Connect** and signs in. A custom app is off by default in every new chat: **+** and tick Lenz. Naming Lenz in the question is what makes ChatGPT reach for it rather than answer from memory. ### MCP Inspector (try the tools by hand) ```bash npx @modelcontextprotocol/inspector # Transport: Streamable HTTP ยท URL: https://lenz.io/mcp # Header: Authorization: Bearer ``` ## Example > **You:** Is it true that honey never spoils? > > The assistant calls `assess_claim("Honey never spoils")` and gets back: > *Mostly True* โ€” high confidence. Properly sealed honey can keep effectively > indefinitely thanks to its low moisture and acidity; the caveat is contamination or > added water. For a sourced deep-dive it can escalate with `verify_claim`. ## Credits Every tool call draws on **one pool of credits** on your Lenz account. There is no separate budget per tool: spending on `assess_claim` reduces what is left for `verify_claim`, and vice versa. `check_usage` returns the balance (`credits_remaining`) alongside `costs`, the live price list โ€” read the weight from there rather than assuming one. `verify_claim` is the expensive path by an order of magnitude; `assess_claim` and `ask_followup` are the cheap ones. `verify_claim` also takes an optional `depth`: `"low"` runs a shallower research pass โ€” fewer sources, faster, the same models โ€” for half the credits of the default `"standard"`. That price sits under `cost_options.verify.depth.low` on `check_usage`. You are charged for the depth you **request**; the `depth` on the completed result is the depth the verdict was **produced** at, so a `"low"` request answered from an existing deeper check reads `"standard"` โ€” the echo describes the evidence, the charge follows the request. `check_usage` also reports `assess_remaining` and `verify_remaining`, which are the SAME balance projected into each tool's own unit โ€” "how many of these could I still make" โ€” not separate allowances. Free keys include a monthly allowance that resets each period; grants and top-ups add non-expiring bonus credits on top, spent only once the allowance is gone. See plans at [lenz.io/plans](https://lenz.io/plans). **When you run out**, tools return `status: "quota_exhausted"` with a `message` and a `manage_url` pointing at the plans page. It is not retryable โ€” the balance is spent until you top up or the monthly allowance resets. An agent should say so plainly rather than retrying or quietly skipping the check. `status: "rate_limited"` is a different thing: a rate limit (today, the per-account daily `extract` cap, which costs no credits at all). That one does clear on its own, and the result carries `retry_after_seconds` telling you when. ## Skills Prefer a guided workflow to calling the tools yourself? The [`lenz-fact-check`](https://github.com/lenzhq/lenz-mcp/blob/HEAD/skills/lenz-fact-check) skill turns "is this true?" into a structured pass โ€” it extracts the checkable claims, runs `assess_claim` on each, escalates high-stakes ones to a deep `verify_claim`, and reports verdicts with confidence and sources (with the directional-not-absolute caveat built in). Point your agent at [`skills/lenz-fact-check/SKILL.md`](https://github.com/lenzhq/lenz-mcp/blob/HEAD/skills/lenz-fact-check/SKILL.md). ## Links - **Website:** [lenz.io](https://lenz.io) - **Get a key:** [lenz.io/api-credentials](https://lenz.io/api-credentials) - **Developer docs:** [lenz.io/developers](https://lenz.io/developers) - **SDKs:** [Python](https://github.com/lenzhq/lenz-io-python) ยท [Node](https://github.com/lenzhq/lenz-io-node) ## Support Questions or issues? [Open an issue](https://github.com/lenzhq/lenz-mcp/issues) or [get in touch](https://lenz.io/contact). ## License [Apache-2.0](https://github.com/lenzhq/lenz-mcp/blob/HEAD/LICENSE) ยฉ lenzhq. The Lenz name and logos (`assets/`) are trademarks of lenzhq and are not granted by the license โ€” see [NOTICE](https://github.com/lenzhq/lenz-mcp/blob/HEAD/NOTICE). ## Maintainer [@Pavel12431432](https://github.com/Pavel12431432)