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

Connect a compatible Streamable HTTP MCP client to the free hosted service for 46 tools covering evidence, aggregate calculations, temporary projects, background jobs, and file handoff. No sign-in is needed to connect. Hosted uploads leave your device, require consent, and use token-protected workspaces whose access expires after 24 hours.

https://mcp.crosstabs.com/mcp

See the MCP setup and privacy boundaries before uploading. Export before expiry; provider backup retention is separate from active-data cleanup. Client-specific compatibility is not guaranteed.

For on-device processing, the MIT-licensed crosstabs 1.4.0 package provides a separate 35-tool headless server and 39 analytical tools plus runtime status on the Python statistics server. These local tool sets are not the hosted 46-tool list.

pip install crosstabs==1.4.0

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.