API Key Onboarding

How to get an API key for the Developer, Business, or Enterprise tier, end to end. Developer and Business are card subscriptions: you check out, your key is created automatically the moment the subscription starts, and it is shown to you on the confirmation page — no form, no approval step, no waiting. Enterprise stays email-led, because negotiated allowances and terms need a conversation before a key exists. And if you only need a free key, you can create one yourself in a single click without talking to us at all.

How it works

The whole flow, at a glance:

1. You pick a tier — per the published rate card. Anonymous and the free key need no account at all; Developer and Business are monthly subscriptions; Enterprise is negotiated
2. You subscribe — a hosted card checkout run by our payment provider, who is the merchant of record. Card details never touch our servers or our browser code
3. Your key is created automatically — the subscription notifies our API, which mints your key and stamps it with your tier's allowance. This takes seconds, not a business day, and nobody has to be awake for it
4. You copy your key from the confirmation page — and it stays retrievable there for 24 hours if you close the tab. We store only a SHA-256 hash, so keys are never emailed; there is nothing on our side to send
5. You plug the key into your MCP client — standard Authorization: Bearer <key> header, no client-code changes beyond that
6. We stay in touch — direct support channel, and a check-in if your usage suggests a different tier would fit better

The whole thing is designed to be low-ceremony. If a paid key doesn't make sense yet, the anonymous tier is free and returns byte-identical math — tell us what you're building and we will say so honestly rather than sell you a plan you don't need.

Step by step

Step 1 — Choose a tier and subscribe

Pick the tier that fits from the rate card — Developer ($19/mo), Business ($99/mo), or Enterprise (custom) — and start the subscription from that page. Checkout is hosted by our payment provider, who acts as merchant of record for the sale: card details never touch our servers, our browser code, or our logs. They also handle the tax treatment, the receipt, and the customer portal where you can later change your card or cancel.

You do not need your MCP client wired up first, and you should not take our word for the numbers: verify the math on the anonymous tier before you pay anything. It runs the identical engines with no signup, and the anonymous-parity invariant guarantees the answers are byte-identical to what a paid key returns.

Step 2 — Your key is created automatically

For Developer and Business, the moment the subscription becomes active our payment provider sends a signed notification to our API, which verifies the signature, creates a key, and stamps it with your tier's daily cap and short-term ceiling from the published rate card. Nobody has to be awake for this; it happens in seconds. Renewal payments extend the key automatically, and a failed payment does not cut you off — the provider runs its normal retry process first.

For Enterprise, we set up a short scoping call (or continue by email if you prefer) to align on:

• Allowance shape — negotiated daily caps and short-term ceilings beyond the published numbers, sized to your expected load — and, if you need throughput actually reserved rather than drawn from the shared gateway pool, what provisioning that would cost
• Key topology — separate staging and production keys you can monitor and revoke independently
• Terms — agreement language layered on top of LICENSE-API.md, plus any procurement or security-review paperwork your side needs

Step 3 — You collect your key from the confirmation page

Checkout returns you to digitalcalculator.info/mcp/key/, which displays the key that was just created for you. It stays retrievable at that same link for 24 hours, so closing the tab by accident is recoverable — open the link again and it will still be there.

For Enterprise, where the key is issued by hand as part of the scoping outcome, we agree a secure delivery channel with you first — a 1Password shared item, a Signal message, or PGP-encrypted email. Never plaintext email, and never a shared Slack channel.

Step 4 — Plug the key into your MCP client

The endpoint is the same as the anonymous tier — https://mcp.digitalcalculator.info/mcp — but every request now carries an Authorization header:

curl -X POST https://mcp.digitalcalculator.info/mcp \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer <YOUR_KEY_HERE>' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"mortgage_monthly_payment","arguments":{"principal":300000,"annualRatePercent":6.5,"termYears":30}}}'

If you're integrating via an MCP client library, look for its Bearer / API-key config option:

• Claude Custom Connectors — add the key under the connector's "Authentication" field when creating the connector in claude.ai
• MCP Inspector — add the header via the transport configuration panel
• Raw HTTP / SDK — set Authorization: Bearer <key> on every POST to /mcp
• npm shim (@markcolabs/mcp) — the shim forwards the Authorization header from your client to the hosted endpoint; set it in your MCP client config as usual

Once the key is in place, tool responses are byte-identical to what the anonymous tier returns for the same inputs — per the anonymous-parity invariant. What changes is your allowance (your tier's per-key daily cap and short-term ceiling — a budget counted against your key alone, not reserved bandwidth: the gateway throttle stays shared), the per-key attribution, and the support relationship. See the API Reference for the tool schemas; nothing about the tool contracts changes for authenticated calls.

Step 5 — Ongoing support and changes

After the key is live:

• Support — you have a direct email channel with the maintainer; Business keys get priority triage
• Tier changes — if your usage grows past the Developer limits (or shrinks below them), change the plan or email us; your key stays the same and only its allowance changes, so nothing in your integration needs redeploying
• Cancellation — cancel in the provider's customer portal or email us. Your key keeps working until the end of the period you have already paid for, and is switched off when that period ends — not at the moment you click cancel. The anonymous tier remains open to you
• Feedback — if you hit rough edges, tell us; the roadmap (SLAs, self-serve portal, key rotation UI) is prioritized by what paying integrations actually need

What we ask of you

A paid key is a two-way commitment. From your side, we ask:

• A note on what you're building — nothing in checkout asks for it, and nothing is gated on it, but a one-line email telling us is how we size limits sensibly and prioritize the roadmap around real integrations rather than guesses
• Willingness to give feedback — if something doesn't fit, tell us; that is more valuable than silent churn
• Reasonable security hygiene on the key — store it in a secrets manager, don't check it into git, ask us to rotate it if a laptop is lost

FAQ

Can I test the tools without an API key first?

Yes — that is exactly what the anonymous tier is for. Point your MCP client at https://mcp.digitalcalculator.info/mcp with no Authorization header and every tool works. Use the anonymous tier to verify the tool outputs meet your accuracy expectations before you pay for anything. The math is byte-identical between anonymous and authenticated responses (anonymous-parity invariant).

Do you offer free trials of the paid tiers?

The anonymous tier is the trial — it runs the identical math with no signup, so you can validate correctness for free before subscribing. There is no "free trial that auto-converts to paid": every paid subscription starts explicitly, with you entering a card, at the published price.

How does billing work?

A monthly card subscription at the rate card price, charged by our payment provider, who is the merchant of record — they are the seller on your receipt, they handle any applicable VAT or sales tax, and they own the customer portal where you change your card or cancel. If your organization needs invoicing rather than a card (PO numbers, net terms), email us and we will arrange it manually instead.

What happens if I lose my key?

Within 24 hours of checkout, re-open the confirmation page link and the key will still be shown. After that it is gone for good — keys are stored server-side as a SHA-256 hash, so we do not have the plaintext either, and there is no email in which to go looking for it. Email us and we will revoke the old key and issue a replacement; your subscription is unaffected. There is no self-serve rotation UI yet; that is on the roadmap.

Can I get multiple keys for staging and production?

On Enterprise, yes — separate staging and production keys you can independently monitor and revoke are part of the standard shape. On Developer and Business a subscription provisions one key; email us if you need a second one for staging and, depending on your setup, we can usually accommodate it. A free key is often the right answer for a staging environment.

References

• Pricing — the published rate card and feature comparison
• Versioning contract — SemVer policy, anonymous-parity invariant, deprecation window
• API Reference — input schemas and output shapes for all 9 tools
• Quickstart — first call in under 5 minutes (anonymous tier)
• Your API key — where a paid key is shown after checkout, and for how long it stays retrievable
• FAQ — general questions about the server

Ready to start? Pick a tier on the rate card — or, for a free key, create one yourself in a click. Until card checkout is switched on (see the note above), email admin@markcolabs.com with the tier you want and we will set you up at the same published price.