Free preview, paid run: a Cloudflare MCP server over Sume

If you sell Sume-backed work through a Cloudflare MCP server, expose two tools: a free one that returns an estimate, and a paid one that runs the job. Cloudflare's x402 docs say free and paid tools can be mixed on one server. Sume's dry_run gives the free half, because it returns an admission and cost preview without submitting a job.

The buyer's agent can then decide whether the quoted price is worth paying before any payment is requested.

The two tools

Why split it

A single paid tool forces buyers to pay before they know what the job costs. Splitting lets your server quote first. Sume documents dry_run as the preview and max_spend_usd as an optional cap that is enforced only when sent (tools and gates), so pass both in your handlers: the estimate to set the quote, and the cap to bound the run.

Keep the quote and the cap consistent. If the estimate says $0.40, price the paid tool above that and cap the run at or under your own cost limit.

Pitfalls

• A quote is an estimate; admission can still return queue_full or rate_limited, so plan a retry path (generation admission).
• Do not reuse one idempotency_key for different jobs.
• Test the whole flow on base-sepolia before mainnet.
• Your price must cover your own cost, which the free estimate tool should not give away for free if it is sensitive.