Spillmark

Spillmark for AI agents

Connect an AI assistant or a script to Spillmark over MCP or a plain REST API. Anyone can use the free calculators. A brand's own agent can read its measured lift, next test plan, locked predictions and recommendations with a read-only key.

Server URL

https://spillmark.com/mcp

Streamable HTTP. No key needed for the public tools; add a brand key as a bearer token for the brand tools.

Connect

Claude and ChatGPT: add a custom connector with the server URL above (public tools).

Cursor: add to .cursor/mcp.json. Leave out headers for the public tools.

{
  "mcpServers": {
    "spillmark": {
      "url": "https://spillmark.com/mcp",
      "headers": { "Authorization": "Bearer sm_…" }
    }
  }
}

Claude Code:

claude mcp add --transport http spillmark https://spillmark.com/mcp --header "Authorization: Bearer sm_…"

REST: the same tools at https://spillmark.com/api/v1, which lists each tool with its input schema.

curl -X POST https://spillmark.com/api/v1/run_calculator \
  -H "Content-Type: application/json" \
  -d '{"slug": "holdout-test-calculator", "inputs": {"regions": 30, "lift": 15}}'

curl https://spillmark.com/api/v1/get_lift -H "Authorization: Bearer sm_…"

Public tools

No key. Up to 300 calls an hour from one address. The calculators are the same ones at /tools, and each result links back to the calculator with the same inputs.

  • list_calculators

    Spillmark's free Amazon and Meta ads calculators (holdout test size, incremental ROAS, break-even ROAS, ACoS, TACoS, Amazon fees and profit, LTV and CAC), with each one's inputs and example values. Use run_calculator to run one.

  • run_calculator

    Runs one calculator from list_calculators on your numbers and returns the headline result, the supporting figures, a one-sentence reading, and a link that opens the calculator with the same inputs. Missing inputs use the calculator's example values. Enter percents as points (15 means 15%), choices as the option index.

  • how_lift_is_calculated

    Spillmark's method in brief: how a geo holdout test measures the sales Meta ads cause on Amazon, with links to the full method and a sample report on made-up numbers.

Brand tools

In private beta for Spillmark brands. Ask at hello@spillmark.com.

  • get_brand

    The brand this API key reads for: its name, today's date in the brand's time zone, which data sources are connected and when each last synced, and a dashboard link.

  • get_lift

    What this brand's Meta ads cause on Amazon (and Shopify, when tested): each holdout test's lift and extra orders a day with 95% ranges and its locked design hash, the ongoing Meta→Amazon effect estimate against break-even, and incremental CAC from the latest completed test. Null fields mean there's no result yet.

  • get_test_plan

    The next holdout test Spillmark recommends for this brand: start and end dates, which states keep ads on and which pause, the options by holdout size with what each costs and the smallest lift it can detect, and any sales events or stock-outs overlapping the window.

  • get_track_record

    Every prediction Spillmark locked for this brand (the change, the predicted figures with 80% ranges, the actual result once scored, and whether the stored file still matches its lock hash), how many landed in range, and whether the brand's hash-chained ledger verifies.

  • get_ledger_export

    This brand's whole ledger (pre-registered designs, results, locked predictions and their scores) as a self-contained bundle with its hash chain, timestamps and the steps to verify it independently. Large; use get_track_record for a summary.

  • list_recommendations

    Changes Spillmark has recommended for this brand, each with why, the data used, its locked prediction, guardrail checks and how to make it, plus 7- and 14-day results for changes the brand made. The brand approves and makes every change; this only reads.

What agents get, and what they don't

  • Results, not raw data: lift with its 95% range and the test's locked design, plans and predictions. No order-level, customer or ad-account records.
  • Read only. No tool changes ads, budgets, orders or settings. Spillmark recommends; the brand makes every change.
  • Every number keeps its uncertainty, and predictions show misses as well as hits.
  • Owners see which tool each key called and when, and can revoke a key at any time. Calls log the tool name, not what it returned.
  • A key stops working when it's revoked or its creator loses access to the brand.

How the numbers are made: See exactly how lift is calculated.