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One identifier in. One value and its reason out.

A flag key, an identifier, and attributes go in. A typed value and the reason for that value come out. The same input always produces the same output.

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Context received
test
checkout_v2
Context
environment
production
user_id
usr_142
plan
pro
country
DE
Rules · same input, same path, every time
Rule 1environment is stagingpending
Rule 2plan is enterprisepending
Rollout25% by user_idpending
What it does

Real product states, not a promise.

A flag key, an identifier, and attributes go in. A typed value and the reason for that value come out. The same input always produces the same output.

  • Rules evaluated in order
  • Typed values: boolean, string, number, JSON
  • Environment-aware values
  • Reason and matched rule returned
Input

Flag key, identifier, and attributes

Output

A value and the reason for that value

Where it fits

Where it fits

01

Feature gating

02

Remote configuration

03

Per-plan behaviour

API example

One request.

POST /v1/flags/evaluate. The full request and response contract is in Flowyn Docs.

POSThttps://api.flowyn.dev/v1/flags/evaluate200
curl -X POST https://api.flowyn.dev/v1/flags/evaluate \
  -H "Authorization: Bearer flw_test_••••" \
  -H "Content-Type: application/json" \
  -d '{
    "key": "checkout_v2",
    "identifier": "usr_142",
    "attributes": {
      "plan": "pro"
    }
  }'
Percentage rolloutPercentage rollouts

Frequently asked questions

Where is the exact request contract for Deterministic evaluation?
In Flowyn Docs and the OpenAPI document at https://api.flowyn.dev/openapi/v1.yaml. This page shows the request; the docs page lists every field, status value, error, and limit.
Is evaluation deterministic?
Yes. The same flag configuration, identifier, and attributes always return the same value. Rollouts hash a stable identifier into a bucket.
Who supplies the attributes?
Your application. Flowyn evaluates what you send and never guesses user attributes.

Build with Deterministic evaluation.

Create a workspace, make your first call in the test environment, and inspect every attempt.

Start building Read the docs