Soulfield Lens — MCP server

Outside-in validation for AI-generated text, as an MCP tool.

Every AI tool asks the same model that wrote the answer whether it's any good. It says yes. The Soulfield Lens is outside-in: a separate model runs a fixed gate over your output. It checks text — it doesn't write it. This package puts that gate inside Claude Code, Cursor, and any other MCP-compatible agent, so output can be validated on the path where it's generated.

The gate is fail-closed: a borderline case returns UNKNOWN, never a silent pass. There is no generation step, so it can't fabricate claims of its own — only check. It can still be wrong about a judgment; that is exactly why borderline cases return UNKNOWN instead of a confident yes.

This is a thin stdio wrapper around the hosted Lens API (api.soulfield.one). No local model, no build step — one file, two dependencies.

Try it before you install anything

The keyless demo endpoint runs the same gate — a few runs a day per IP, no signup:

curl -s https://api.soulfield.one/v1/demo \
  -H 'content-type: application/json' \
  -d '{"text": "<paste the AI output you are about to ship>"}'

Install

npm install -g @soulfield/lens-mcp

Or run without installing: npx @soulfield/lens-mcp.

Claude Code

claude mcp add soulfield-lens \
  -e SOULFIELD_API_BASE=https://api.soulfield.one \
  -e SOULFIELD_API_KEY=<your-key> \
  -- npx @soulfield/lens-mcp

Any MCP client (JSON config)

{
  "mcpServers": {
    "soulfield-lens": {
      "command": "npx",
      "args": ["@soulfield/lens-mcp"],
      "env": {
        "SOULFIELD_API_BASE": "https://api.soulfield.one",
        "SOULFIELD_API_KEY": "<your-key>"
      }
    }
  }
}

Production calls need an API key — request one at hello@soulfield.one. lens_health works without one.

Tools

Tool	What it does	Auth
validate_content	Runs the outside-in gate over text. Returns pass/fail, score, per-dimension results, and violation details with reasoning. Optional domain (general, finance, marketing, legal, seo, agency) and context (audience/purpose).	key
scrub_pii	Regex-only PII scan (emails, phone numbers, card numbers, …). Returns scrubbed text plus findings. Instant — no LLM call.	key
lens_health	Checks the Lens API is up. Returns status and version.	none

What you get per run: receipts — what was checked, what passed, what was held, and why. Machine-readable, not a badge. We won't hand you a guaranteed accuracy number for your data: scores don't transfer across models, datasets, and runtimes, and a tool that promises a fixed figure on data it has never seen is making the exact claim this gate exists to catch.

Long inputs

Inputs of ~4,000 characters and up are submitted as an async job and polled to completion automatically, so a single long validation never dies on a request timeout. Short inputs use the fast synchronous path. No configuration needed.

Configuration (env vars)

Variable	Default	Purpose
SOULFIELD_API_BASE	http://localhost:8002	Lens API base URL. Use https://api.soulfield.one for the hosted service, or your own deployment.
SOULFIELD_API_KEY	—	Required for validate_content and scrub_pii.
SOULFIELD_VALIDATE_TIMEOUT_MS	180000	Per-request timeout for the sync path.
SOULFIELD_VALIDATE_BUDGET_MS	600000	Total wall-clock budget for the async poll loop.
SOULFIELD_ASYNC_MIN_CHARS	4000	Input length at which the async path kicks in.

The rest of the product

This wrapper is one of several surfaces on the same engine:

• Free one-output audit — api.soulfield.one/audit. The audit is the demo.
• Wire it in (SDK stop-hook and middleware) — api.soulfield.one/developers.
• Own it — the kit: lenses, compiler, self-improve loop, validator agent, Apache-2.0. Train it on your own data. Start at api.soulfield.one.

We hold our own marketing copy to the same gate this package exposes.

License

MIT — see LICENSE. (The lens-kit product is licensed separately under Apache-2.0.)