# Identifiers

How Polyester ConnectRPC contracts represent public IDs as fixed64 values in typed payloads.

Polyester Protobuf contracts commonly declare public IDs as `fixed64` values, carrying the underlying unsigned 64-bit value in compact typed payloads.

For what public IDs are and why they are opaque, see [Public IDs](https://testnet.polyester.com/docs/developer-docs/shared-concepts/public-ids). This page covers only how they look and behave over ConnectRPC and Protobuf.

## Using fixed64 IDs

Public ID fields declared as `fixed64` carry the underlying unsigned 64-bit value. Always follow the field type in the published contract; not every identifier uses `fixed64`.

```protobuf
message Trade {
  fixed64 order_id = 1;
  uint32 symbol_id = 2;
  uint64 qty_scaled = 3;
}
```

In generated clients, use the type your language SDK gives you for 64-bit integers. In JSON debug mode, protobuf tools often show 64-bit integer fields as decimal strings:

```json
{
	"orderId": "72623859790382856"
}
```

JSON debug output shows the fixed64 value as a decimal string because JSON has no native 64-bit integer type. In binary protobuf, the same values are encoded as fixed-width 64-bit fields. This keeps hot paths compact and avoids extra string parsing in clients that already use typed protobuf contracts.

Using an integer field instead of a string also reduces payload size, especially in large list responses, order history, trade history, realtime-style snapshots, and other payloads that repeat many IDs. If your integration cares about smaller payloads and lower transport overhead, prefer ConnectRPC with binary protobuf.

## Displaying and converting IDs

If a directly generated ConnectRPC client also renders user-facing URLs or labels, convert its `fixed64` values to base58 in the display layer. Official SDKs can expose a normalized representation instead, so follow the selected SDK's documented types. For example, the TypeScript SDK returns base58 public-ID strings to application code even when its underlying transport is ConnectRPC.

Conversion is needed only when an ID crosses between a raw ConnectRPC field and a base58 surface such as REST or URLs (see [REST identifiers](https://testnet.polyester.com/docs/developer-docs/rest/identifiers)). Base58 `An6UebxCZd` and decimal `72623859790382856` are two representations of the same unsigned 64-bit public ID. A custom converter must reject invalid Base58 characters and values larger than `uint64`.

> **Public IDs are not credentials**
>
> Public IDs are safe to expose as identifiers, but access to private resources still requires valid authentication and authorization.