Free statistics API

Quick start

Pass your observed counts as a matrix. Rows are separated by ;, cells by , — the same format used by shareable calculator links.

# GET — table in the query string
curl "https://www.crosstabs.com/api/v1/chi-square?d=20,30;30,20"

# POST — table as JSON
curl -X POST https://www.crosstabs.com/api/v1/contingency \
  -H "Content-Type: application/json" \
  -d '{"table": [[20, 30], [30, 20]]}'

Response (abridged):

{
  "input": { "table": [[20, 30], [30, 20]], "n": 100, "rows": 2, "cols": 2 },
  "chiSquare": { "chiSquare": 4.0, "degreesOfFreedom": 1, "pValue": 0.0455 },
  "cramersV": { "value": 0.2, "label": "small" },
  "fishersExact": {
    "pValue": 0.0713,
    "oddsRatio": 0.4444,
    "oddsRatioState": "finite",
    "oddsRatioCI": [0.2007, 0.9837],
    "oddsRatioCIStates": ["finite", "finite"]
  },
  "fishersExactUnavailableReason": null,
  "docs": "https://www.crosstabs.com/developers"
}

Endpoints

Limits & conventions

• Inferential endpoints accept 2×2 through 12×12 finite, non-negative tables with positive margins and N ≤ 1,000,000,000,000.
• Fisher uses the two-sided Fisher–Irwin fixed-margin probability ordering for safe-integer counts and enumerates at most 100,000 feasible tables; larger supports return a machine-readable workload_limit reason (HTTP 422 on the dedicated exact endpoint).
• 30 requests per minute per IP. Need more? See the support page.
• The odds-ratio endpoint encodes unbounded zero-cell results as a null numeric value plus an explicit positive_infinity state.
• Calculation behavior and assumptions are summarized on the methods page and match the workspace and calculators.
• Free for any use, including commercial. Please don't use it as a high-volume backend without getting in touch first.

See Methods for calculation behavior and assumptions. Email support@crosstabs.com to reach us, or use the support checklist.

MCP server for AI assistants

Want Claude, ChatGPT, or your own agent to run numerical contingency-table routines? The MIT-licensed crosstabs MCP package registers 39 analytical tools plus runtime status (40 Python functions total), spanning exact, asymptotic, and simulated tests, effect sizes, agreement measures, and power analysis over the Model Context Protocol.

pip install crosstabs

The separate local Codex/Claude plugin repository is at barangaroo/crosstabs-codex-plugin. Package 1.4.0 has verified fresh public installs, including 35 local project tools. Guided weighting preview and apply are available with explicit population targets and recorded human confirmation; saving a sampling weight does not approve a survey design or authorize ordinary inference. Plugin source availability, native-host review and directory approval are separate. Exact status, setup instructions, and verified parity boundaries are on the MCP server page.