# tracestate-malformed

The **`tracestate`** of an event is **not valid** under W3C Trace Context.

- **Route:** `write-events`
- **Description:** one of these texts, which names the rule that the value breaks:
  - `tracestate is malformed: expected at most 32 members, as W3C Trace Context defines`, when it has more members
  - `tracestate is malformed: expected each key at most once, as W3C Trace Context defines`, when a key repeats
  - `tracestate is malformed: expected a comma-separated list of key=value members as defined by W3C Trace Context`, for any other mistake
- **Details:** **`event`**, the place of the event in its list, counting from 0, and **`value`**, the `tracestate` as the request gave it.

## Why It Happens

A `tracestate` carries vendor-specific data of a distributed trace as a **comma-separated list of `key=value` members**, with **at most 32 members** and **each key at most once**, see **[Integrating OpenTelemetry](/docs/eventsourcingdb/integrating-opentelemetry#trace-context-format)**. A key is made of lowercase letters, digits, `_`, `-`, `*`, and `/`, starting with a letter, or has the form `tenant@system`, and a value is 1 to 256 printable ASCII characters other than commas and equal signs, not ending in a space.

A typical cause is a member with another separator than the equal sign, such as `rojo:00f067aa0ba902b7`, or a key with uppercase letters.

## How to Fix It

Send the `tracestate` as W3C Trace Context writes it, which tracing libraries such as OpenTelemetry do, or leave it out. Sending the same request again fails the same way, since the error depends on the request alone.

## Example

For a write whose first event has the `tracestate` `rojo:00f067aa0ba902b7`, with a colon instead of an equal sign, EventSourcingDB answers with this error, as a line of the stream, and then ends the stream with its `end` item:

```json
{
  "type": "error",
  "data": {
    "code": "https://docs.eventsourcingdb.io/errors/tracestate-malformed",
    "description": "tracestate is malformed: expected a comma-separated list of key=value members as defined by W3C Trace Context",
    "details": {
      "event": 0,
      "value": "rojo:00f067aa0ba902b7"
    }
  }
}
```