Blekline
v0.3.0GitHub

MCP

Cursor

P0 — MCP setup for all Cursor models and modes.

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P0 — primary MCP client. Works in Agent, Composer, and Chat across all models.

Setup

Step 1. Build packages (first time only):

pnpm install && pnpm build:packages

Step 2. Set environment variables in your shell:

export BLEKLINE_WORKSPACE_TOKEN="blw_..."
export BLEKLINE_API_URL="https://app.blekline.com"

Step 3. .cursor/mcp.json is pre-generated in the repo root. Reload Cursor: Cmd+Shift+P → Developer: Reload Window

Step 4. Verify in Settings → MCP: blekline should show green with 3 tools: blekline_mask_prompt, blekline_classify_risk, blekline_emit_event.

What the tools do in Agent mode

When your agent runs, Blekline intercepts at two points:

Before model context — blekline_mask_prompt strips PII and secrets from any text before it enters the context window.

Before tool execution — blekline_evaluate_tool_call checks the tool name and arguments against your workspace policy before the call reaches Daytona or any downstream MCP server.

You don't need to change your prompts or agent rules. The MCP server handles interception automatically when connected.

Troubleshooting

MCP shows red / disconnected

  1. Run pnpm build:packages — the dist files must exist for the stdio command.
  2. Check BLEKLINE_WORKSPACE_TOKEN is exported in your terminal session, not just in .env.
  3. Try the npm path instead: set command to npx and args to ["-y", "@blekline/mcp-server"].
  4. Reload Cursor after any config change: Cmd+Shift+P → Developer: Reload Window.

Tools show but calls fail with 401

Token scope issue. Regenerate a token in Admin → API keys with mask:write and events:write scopes.

Agent never calls the Blekline tools

In Agent mode, tools are available but the agent decides when to invoke them. Add a rule to .cursorrules or your system prompt: Always call blekline_mask_prompt before sending any text containing emails, API keys, credentials, or database connection strings to a model.

Using with Daytona sandboxes

Connect blekline-proxy as a second MCP server. It sits between Cursor and the Daytona MCP server, enforcing tool policy before sandbox execution. See MCP Proxy and Daytona Stack.

Model coverage

MCP is model-agnostic. One Blekline server covers all Cursor models: Anthropic (Opus, Sonnet, Haiku), OpenAI (GPT-4o, GPT-5, o1/o3), Google (Gemini Pro/Flash), Cursor (Composer, Auto). See Cursor Model Matrix for the enterprise QA checklist.

Next steps: Quick start · MCP Proxy · Daytona stack · Open workspace