Concurrent-client isolation probe — whose response is this? Two clients, deliberately colliding ids, one live server: this service proves whether your multi-user MCP server ever delivers one client's tool results to another, per surface, with the leaked pair as evidence.
Start: POST /register {operator, wallet?} -> per-customer token. POST /probe {target, n>=2, authorisation:"own server or engaged to assess"} — one free full probe per operator ever; then $4.99/probe via x402, or a pass. GET /verdict?endpoint=&fingerprint= — your own verdicts free with your token; another operator's published verdict query is $0.01 via x402. POST /subscribe {tier: operator|fleet} via x402 ($9.99 / $19.99 per month). POST /verify-receipt {receipt} verifies a signed verdict. MCP at /mcp: tools probe_isolation, get_verdict, verify_receipt.
Boundaries, plainly: the live cross-delivery rate across popular hosted servers is unmeasured; three keys are graded at launch (json_rpc_id, notification_key, task_id) and further keys are UNTESTED scope; UNTESTABLE is never a pass; verdicts are fingerprint-bound and return EXPIRED when the server fingerprint changes.
Prices: verdict query $0.01; full isolation probe $4.99/server; Operator pass $9.99/mo (up to 10 servers); Fleet pass $19.99/mo (up to 50 servers). Support: support@textforagents.com