---
title: "Bootstrap"
method: POST
path: "/api/experiments/bootstrap"
tags: ["Experiments"]
---

# Bootstrap

`POST /api/experiments/bootstrap`

Materialise visitor ``ab_arms`` and mirror them into cookies.

Body:
  - ``device_id`` (optional; falls back to the ``explee_device_id``
    cookie). Empty/missing → 400 — nothing to bucket. Capped at
    64 chars (see :class:`BootstrapRequest`).
  - ``missing`` (optional list of exp ids to enrol into; defaults
    to all active visitor experiments).
  - ``overrides`` (optional ``{exp_id: arm}``; honoured only when
    ``_is_override_allowed`` returns True).

Side effects:
  - ``find_or_create_guest_user(device_id)`` — race-safe insert.
  - Override pass (if allowed): JSONB-merge over existing keys
    (REWRITE semantics).
  - Enrol pass: JSONB-merge skipping any key already present
    (snapshot lock).
  - Set-Cookie ``ab_<exp_id>=<arm>`` for every key in the response
    on the host's cookie-domain (``.explee.com`` /
    ``.explee.local`` / host-only on localhost or sandbox env).

Returns the post-write ``{exp_id: arm}`` snapshot. Idempotent —
calling twice yields the same result (and emits the same
Set-Cookies).

## Request body

- BootstrapRequest
  - `device_id` string, nullable
  - `missing` string[], nullable
  - `overrides` object, nullable

## Response `200`

Successful Response

- ApiExperimentsRouterBootstrapResponse
  - `device_id` string, required
  - `arms` object, required

## Other responses

- `422` — Validation Error

---

[API](https://skmtc.dev/explee/apis/explee-api.md) · [All operations](https://skmtc.dev/explee/apis/explee-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/explee/explee-api/revisions/f169bc6e9447/schema)