Connect an MCP client

Install the portable CLI:

cargo install jacs-cli --locked
jacs mcp

For clients that accept an mcpServers configuration, the verification-only connection is:

{
  "mcpServers": {
    "jacs": { "command": "jacs", "args": ["mcp"] }
  }
}

The host starts a local stdio process. There is no HTTP listener; diagnostics go to stderr. The only default tool is jacs_verify_document. Select the signer's public evidence independently, parse the returned JSON text, and check its valid field. See the verification use case.

Enable local signing explicitly

Create an encrypted agent in a private directory from a terminal:

mkdir -m 700 .jacs
jacs create --output .jacs/agent.json > public-identity.json
jacs mcp --profile local-sign --agent .jacs/agent.json

The terminal prompts for the password. A noninteractive MCP host must supply JACS_PRIVATE_KEY_PASSWORD through its secret-handling mechanism; do not put passwords in tool arguments, command arguments or committed client config. Use an absolute vault path in the client's process configuration.

Local signing enables all seven portable tools for the selected vault. Rotation and re-encryption additionally need the destination password at startup through JACS_NEW_PRIVATE_KEY_PASSWORD. The host owns approval of that process-level grant. Unix vault permissions are enforced; platforms without the required filesystem custody adapter can still verify public data.

For agreements and text/images, choose the separate extended MCP profiles. For service integration, use the direct libraries.