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Jevcore MCP

Exposes typed Jev judgments over stdio MCP, returning calibrated probabilities through offline or opt-in live providers.

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Install Jevcore MCP

Pick your client, then add it in one click or paste the config.

STDIONode.js
~/Library/Application Support/Claude/claude_desktop_config.json
claude_desktop_config.json
{
  "mcpServers": {
    "jevcore-mcp": {
      "command": "npx",
      "args": [
        "-y",
        "jevcore-mcp"
      ]
    }
  }
}

Settings → Developer → Edit Config, merge this into mcpServers, then fully quit and reopen Claude Desktop.

Automated check passed— started and listed 3 tools correctly (Today).

Overview

The jevcore-mcp MCP server exposes Jev's typed judgment layer to MCP hosts through a stdio executable. Its three tools ask questions, rank candidates, and check claims, returning typed probabilities rather than prose. It uses an offline mock provider by default, while live TypeSafe or OpenRouter access requires explicit configuration and credentials. Reach for it when an agent needs structured judgments from a plain MCP-compatible host instead of a chat-style response.

Use cases

  • Ask typed yes/no questions from an MCP-compatible agent
  • Rank candidate options with calibrated probabilities
  • Check claims against supplied evidence
  • Run synthetic offline judgments without network access
  • Route judgments through TypeSafe or OpenRouter when configured

Key features

  • Stdio MCP transport
  • Typed ask, rank, and check tools
  • Offline mock provider by default
  • TypeSafe and OpenRouter provider routes
  • Startup egress reporting
  • Best-effort sensitive-data redaction

Tools3

What Jevcore MCP lets your agent do. Expand a tool for its parameters.

Verified live~1.5k tokens of context

Security & health

What it can reach and how reliably it runs — from our own checks, not the maintainer’s claims.

ActiveLast checked Today

Recent health check succeeded.

What it can do

From the 3 tools this server returned when we ran it.

Read-only tools · 3
Network at startup3 connections
Files written at startupNone
Install scriptsNone
npm provenanceNot published
Package age34 days
Maintainers1

Observed 2026-10-24 in an isolated sandbox. A description of reach, not a security audit.

Supply-chain signal

No high-severity advisories surfaced by our automated scan.

Critical 0High 0Medium 0Low 0

Scanned 2d ago via OSV.dev · jevcore-mcp (npm)

Adoption & maintenance

Factual signals from GitHub, npm, and our automated checks — not a rating.

GitHub stars102Stargazers on the source repository.
npm downloads1.9kPackage downloads in the last 30 days.
Last commit5d agoMost recent push to the default branch.
Availability100%Our rolling endpoint + install checks that succeeded.
Install checkPassedOur sandbox started it and listed its tools.
Tools exposed3Callable tools this server registers over MCP.
Directory activity1 viewsConfig copies, upvotes, and views on AllMCPs.

How Jevcore MCP works

What the jevcore-mcp MCP server does

The jevcore-mcp MCP server makes Jev's decision primitives available to MCP hosts that are not running DeepSeek Harness. It provides three typed operations: asking a yes/no-style question, ranking alternatives, and checking a claim against evidence. Results are calibrated probabilities and structured answers, not generated explanations or general-purpose prose.

The MCP package is a thin adapter around the shared jevcore decision layer. This keeps the judgment types, provider selection, policy, redaction, and egress behavior consistent with the project's other adapters. The package requires Node.js 20 or newer.

How it works

Start the server as a stdio process with npx -y jevcore-mcp. MCP messages use stdout as the protocol channel, while startup and egress status are written to stderr. The host can then invoke jev_ask, jev_rank, or jev_check when an agent chooses to use them.

Without provider credentials, the process uses an offline mock. This path makes no network calls and produces synthetic answers. A live provider is selected through environment settings and resolves its credential once during startup. The available routes are TypeSafe directly or OpenRouter when a TypeSafe key is not selected.

Each enabled transmission is reported at startup. Tool calls send the arguments supplied by the model after redaction; ranking includes the query and candidates, while checking includes the claim and evidence. Redaction removes values under recognized sensitive field names and matches several known secret formats before live transmission.

Setup and configuration

The basic setup requires an MCP host that can launch a stdio server and this command:

Terminal
npx -y jevcore-mcp

The provider environment can be controlled with JEV_PROVIDER, using mock, live, or openrouter. TYPESAFE_API_KEY selects the TypeSafe route, and OPENROUTER_API_KEY selects OpenRouter when no TypeSafe key is present. TYPESAFE_MODEL and OPENROUTER_MODEL choose model identifiers; the corresponding *_BASE_URL variables change the API root.

No key is needed for the default mock mode. If JEV_PROVIDER=live is set without a resolvable credential, startup fails rather than silently changing behavior. When embedding the process in DeepSeek Harness, pass credentials through the MCP client's explicit environment map because the harness removes credential-shaped variables from a spawned server environment before merging configured values back in.

Tools and capabilities

The jevcore-mcp MCP server exposes:

  • jev_ask for typed questions using the Jev question surface.
  • jev_rank for comparing a query against candidate options.
  • jev_check for evaluating a claim with supporting evidence.

The tools run only when called by the model. Optional safety and context gates belong to the broader plugin design and are not automatically enabled for MCP use. The MCP transport itself is stdio rather than an HTTP endpoint.

Limitations and notes

Jev is not a conversational model. It is intended for typed judgments, so requests for prose are outside the provided decision surface. The default mock provider is synthetic and should not be treated as a live assessment.

Live use can transmit state and tool inputs to the selected provider. Redaction is best effort: recognized field names and known secret patterns are handled, but an unrecognized secret in free text may pass through. Do not enable the live provider if that residual risk is unacceptable.

The server reports its egress contract on stderr so protocol output remains valid. The tools' transmissions are visible when invoked, but any broader gate behavior should be considered separately because gates can inspect matching tool calls and are opt-in in the project design.

Read the full README View source on GitHub

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Frequently Asked Questions about Jevcore MCP

jevcore-mcp is an MCP server that connects MCP hosts to Jev through a stdio process. It provides three typed tools: `jev_ask` for questions, `jev_rank` for candidate ranking, and `jev_check` for claims with evidence. Results are calibrated probabilities rather than prose, with offline mock execution by default.

Run `npx -y jevcore-mcp` from the MCP client's server configuration. It launches the server over stdio, so the host must support starting a standard stdio MCP process. No credential is required for the default offline mock provider.

Set a provider credential and, when needed, `JEV_PROVIDER` before startup. `TYPESAFE_API_KEY` selects TypeSafe, while `OPENROUTER_API_KEY` selects OpenRouter when no TypeSafe key is present. Setting `JEV_PROVIDER=live` without a resolved credential causes a startup error.

Yes, DeepSeek Harness can launch it through its MCP client configuration. Configure a stdio server with command `npx`, argument `-y jevcore-mcp`, and pass credentials through the client's explicit `env` map because the harness filters credential-shaped variables from spawned processes.

No, it uses an offline mock provider by default and makes no network calls. Network transmission requires an explicitly selected live route and a resolved credential. Startup reports provider and egress status on stderr.

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