Statistics API, OpenAPI & MCP

Choose an interface

• OpenAPI 3.1 JSON specification — GET and POST schemas, operation IDs, errors, bounds, examples, CORS preflight, and health checks for the existing aggregate statistics API.
• Hosted MCP endpoint — a separate 46-tool service. Start with get_started, get_runtime_status, and run_demo_analysis for a synthetic demo without uploads. File uploads need consent and a temporary workspace token.
• Aggregate-only MCP endpoint — five public tools: search, fetch, get_headless_capabilities, analyze_crosstab, and render_crosstab. No respondent rows or private project storage.
• Published local Python package — install crosstabs 1.4.0 and run crosstabs-headless as a stdio MCP server.

MCP clients initialize a connection and use tools/list to discover input schemas. MCP endpoints speak a protocol; opening them in an ordinary browser is not a setup flow. The MCP guide contains client configuration. The OpenAPI document describes the REST endpoints, not the separate hosted workspace API.

# Download the machine-readable REST contract
curl https://www.crosstabs.com/openapi.json

# Check runtime health without sending survey data
curl https://www.crosstabs.com/api/health

# Local stdio MCP (configure this command in your AI client)
pip install crosstabs==1.4.0
crosstabs-headless

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

REST v1 compatibility and deprecation

Public REST v1 compatibility policy: breaking changes use a new major URL prefix rather than silently changing /api/v1. Additive response fields may be introduced; clients should tolerate unknown fields. Current v1 endpoints are not deprecated and have no scheduled sunset. If a deprecation is scheduled, the public changelog and developer documentation will publish the affected endpoints, migration guidance and planned dates. This policy is not an availability SLA or a promise of indefinite service.

Follow the public changelog for published changes. Migration instructions will be linked here when a replacement or scheduled deprecation is announced.

Limits & conventions

• Inferential endpoints accept 2×2 through 12×12 finite, non-negative integer frequency 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).
• POST bodies are limited to 16,384 bytes. The four statistics routes share an in-process limit of 30 requests per minute per client IP; separate serverless instances do not share counters. Infrastructure limits may also apply.
• Unknown /api paths return HTTP 404 JSON with error, code=endpoint_not_found, hint and a documentation link. HEAD returns the status without a body.
• Errors retain a human-readable error string and add a stable code plus an actionable hint. Fisher workload failures retain the analysis fields as well. Do not retry invalid input unchanged.
• GET and POST responses expose RateLimit-Limit, RateLimit-Remaining and RateLimit-Reset. Reset is ceiling seconds until the next sliding-window slot, not an epoch timestamp or full quota reset. On HTTP 429, wait the Retry-After seconds before retrying. These counters are process-local and reset on cold starts.
• 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.