Functionize MCP server vs Steel

Functionize MCP server

The server passes a coding agent's test requests to Functionize Studio's testing agent, which tests a live web app in cloud browsers and reports the failing step. It uses OAuth with read and write scopes and has a no-card free plan. Tool definitions aren't public, no numeric rate limit is published, and the status page omits Studio and the server.

Steel

The hosted API has a public OpenAPI document, per-unit prices, $30 of starting credit and x402 payment for scrape, screenshot and PDF calls. The status page records three API or session-creation incidents of more than an hour in 90 days, and the documented CDP connection puts the API key in the URL.

Functionize MCP server

1. Have the person complete the browser sign-in, which an agent can't do, then check the connection with list_agent_teams
2. Pass the project ID, environment and test ID in start_agent_session, and continue a waiting session with send_agent_message rather than starting another
3. Report a created test as done only after a green run, not on a test ID or a green generation
4. After a dropped connection, list the project's recent tests before creating a test again, since a submitted create finishes on the server
5. Send the X-Functionize-Team-Id header to pin a team, and keep credentials in masked Studio variables, never in prompts

Steel

1. Use POST /v1/scrape for pages you only need to read. It starts no session and costs $5 per 1,000 calls, or $0.01 a call by x402
2. Release every session with POST /v1/sessions/{id}/release and set inactivityTimeout. Browser time bills by the minute, rounded up
3. Build the CDP URL as wss://connect.steel.dev?apiKey=<key>&sessionId=<id> and keep it out of logs, because it carries the key
4. Launch sessions end after 15 minutes at most, and timeout cannot be changed on a live session
5. CAPTCHA solving and Steel's managed proxies on Launch need $10 of paid balance. Free credit does not count