> In order to access the client API endpoints you need to identify yourself. Unless you're using the `none` authentication method, you'll need to [create a CLIENT token](/how-to/how-to-create-api-tokens.mdx) and add an Authorization header using the token.
This endpoint is the one all clients should use to fetch all available feature flags from the _unleash-server_. The response returns all active feature flags and their current strategy configuration. A feature flag will have _at least_ one configured strategy. A strategy will have a `name` and `parameters` map.
> _Note:_ Clients should prefer the `strategies` property. Legacy properties (`strategy` & `parameters`) will be kept until **version 2** of the format.
This endpoint should never return anything besides a valid _20X or 304-response_. It will also include an `Etag`-header. The value of this header can be used by clients as the value of the `If-None-Match`-header in the request to prevent a data transfer if the client already has the latest response locally.
Used to fetch details about a specific feature flag. This is mainly provided to make it easy to debug the API and should not be used by the client implementations.
Before Unleash 4.16, strategy constraints were only available to Unleash Pro and Enterprise users. From 4.16 onwards, they're **available to everyone**.
Strategy definitions may also contain a `constraints` property. Strategy constraints is a feature in Unleash which work on context fields, which is defined as part of the [Unleash Context](/reference/unleash-context.md). The purpose is to define a set of rules where all needs to be satisfied in order for the activation strategy to evaluate to true. A [high level description](https://www.unleash-hosted.com/articles/strategy-constraints) of it is available online.
The example shows strategy constraints in action. Constraints is a new field on the strategy-object. It is a list of constraints that need to be satisfied.
In the example `environment` needs to be `production` AND `userId` must be either `123` OR `44` in order for the Unleash Client to evaluate the strategy, which in this scenario is “default” and will always evaluate to true.
```json
{
"type": "release",
"enabled": true,
"stale": false,
"name": "Demo",
"strategies": [
{
"constraints": [
{
"contextName": "environment",
"operator": "IN",
"values": ["production"]
},
{
"contextName": "userId",
"operator": "IN",
"values": ["123", "44"]
}
],
"name": "default",
"parameters": {}
}
]
}
```
- **contextName** - is the name of the field to look up on the unleash context.
- **values** - is a list of values (string).
- **operator** - is the logical action to take on the values Supported operator are:
- **IN** - constraint is satisfied if one of the values in the list matches the value for this context field in the context.
- **payload** - an optional object representing a payload to the variant. Takes two properties if present `type` and `value`.
- **overrides** - an optional array of overrides. If any context field matches any of the the defined overrides it means that the variant should be selected.
