DEVELOPER PLATFORM

Developer-ready fit intelligence.

A catalog connection, a verified domain, and a script tag. Two browser calls and a key that is safe to ship — built for apparel retailers and platforms.

No SDK required — a script tag and two HTTP calls

Session-based, domain-verified publishable keys

Every response states its own authority

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Last verified: 25 August 2026

POST /b2b/widget/session

X-ShirtMath-Key: pk_live_...
Content-Type: application/json

{ "domain": "yourstore.com" }

→ { "session": "sess_..." }

SAMPLE RESPONSE

{ "status": "VERIFIED_FIT",
  "authority": "PHASE4",
  "current_product": {
    "recommended_size": "M"
  },
  "explanation": "...",
  "candidates": [ ... ] }

The requests and responses on this page are illustrative sandbox shapes, not a customer's traffic. A sandbox workspace receives a clearly-labelled synthetic demonstration carrying authority SANDBOX, so nothing returned in testing is dressed up as a real fit claim. The measuring standard behind any figure the engine compares is set out on the methodology page.

Everything you need

Documentation for every part of the integration

Fit API reference

Complete endpoint docs, parameters, responses, and status codes.

Authentication

Publishable and secret API keys, session lifecycle, and rotation.

Connect your catalog

Sync items and size charts via CSV, JSON, or a custom retailer API.

Size chart integration

Map your size charts and units for accurate recommendations.

Why fit returns happen

Where a fit return actually comes from, and what a comparison can address.

Webhooks & events

Not built yet. Scheduled and manual syncs are the honest answer today — see the FAQ for what is coming soon.

Integrate in three steps

From script tag to a sized recommendation

Create a session

Post your publishable key to open a short-lived signed session, scoped to a verified domain.
Read the reference garment

The widget captures the shopper's reference measurements client-side — nothing is sent until the match request.
Request a match

Send the product reference and the measurements it read. The response carries a size, its authority, and alternatives.

REQUEST EXAMPLE

POST /b2b/widget/match
X-ShirtMath-Session: sess_...

{ "product_ref": "shirt_001",
  "reference": {
    "chest": 20.0, "shoulder": 17.8,
    "length": 39.0
  } }

RESPONSE EXAMPLE

{ "status": "VERIFIED_FIT",
  "current_product": {
    "recommended_size": "M"
  },
  "authority": "PHASE4",
  "confidence": 0.93 }

Not built yet

What a developer should not plan around

ShirtMath is pre-launch. These are named rather than quietly omitted.

No SDKs. The integration is a script tag and two HTTP calls. There is no client library to install.
No webhooks. None of the three implemented catalog connectors registers webhooks yet, so scheduled and manual syncs are the honest answer today.
No Shopify, WooCommerce or BigCommerce app. Those three are declared coming soon and are not built.
No published quotas or service-level figures. Rate limits are settled at integration time rather than invented for a documentation page.
No self-serve checkout. A workspace is set up with you during onboarding — see pricing.

A sandbox workspace receives a clearly-labelled synthetic demonstration carrying authority SANDBOX, so nothing you see while testing is dressed up as a real fit claim. The FAQ answers the rest of the retailer questions, and the ShirtMath for Brands overview is the shortest version of the product itself.

Ready to integrate fit intelligence?

Explore the docs or talk to our team to build the right fit experience for your customers.

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