# syn version
> "Show CLI and server version, and what happens when they differ"

The `syn` CLI ships to npm and the server is deployed separately, so the two can
drift apart. `syn version` reports both sides, and every command that talks to the
API checks the same thing before it runs. Commands that never call the Syntropic
API skip the check: `syn config`, and the marketplace commands, which may still
fetch marketplace registries over the network.

## Output

```bash
syn version
```

Line 1 is always the CLI. Line 2 is the server build that answered at the
configured API URL (`SYN_API_URL`). Against a server on the same release line:

```text
Syntropic137 v0.33.0-beta.1
syn-api 0.33.0b5
```

When the server image was stamped with an image tag or a commit, they follow the
release in parentheses, for example `syn-api 0.33.0 (v0.33.0, abc1234)`.

Line 2 is different when the server could not say which build it is:

| Line 2 | Meaning |
|--------|---------|
| `syn-api 0.33.0b5` | The server reported its release. |
| `syn-api at <url> has no GET /version: a release older than that route, or not a syn-api URL` | `GET /api/v1/version` answered 404. Either the server is too old to report its version, or the URL points at something other than syn-api. |
| `syn-api not reached at <url>: fetch failed` | No answer. The reason after the colon is the network error, or `no answer within <n>ms` on a timeout. |

For example, with nothing listening at the URL:

```text
Syntropic137 v0.33.0-beta.1
syn-api not reached at http://127.0.0.1:1: fetch failed
```

`syn version` exits 0 in every case: it reports what it found. Use
`syn health` to check that the server is reachable and healthy.

## Release skew warning

The CLI and the server match when they share a release line, the major and minor
version. Patch and pre-release differences are ignored, so CLI `0.33.0-beta.1`
and server `0.33.0b5` match.

When the release lines differ, `syn version` prints a warning on stderr after
line 2:

```text
Syntropic137 v0.32.0
syn-api 0.33.0b5
Warning: syn CLI 0.32.0 is talking to syn-api 0.33.0b5. Releases differ (0.32 vs 0.33); commands may fail in ways that look unrelated. Install a matching CLI.
```

Every command that talks to the API makes the same check first, so the warning
appears before anything the command prints, including its own error:

```text
$ syn execution show exec-2d90c10fbdb3
Warning: syn CLI 0.32.0 is talking to syn-api 0.33.0b5. Releases differ (0.32 vs 0.33); commands may fail in ways that look unrelated. Install a matching CLI.
Execution: exec-2d90c10fbdb3
  Workflow:     Test: PR Review with Comment
```

The warning only appears when both versions were read and their release lines
differ. A server with no `GET /version`, a server that cannot be reached, or a
development build of the CLI never produces it.

## When the server predates a command

Two builds on the same release line can still differ by a feature. When a
command calls an API route the server does not have, the error names the server
build and says the server predates the feature, instead of a bare `Not Found`:

```text
$ syn execution sessions exec-b6f4c2b271d0
Error: Failed to read session inventory: syn-api 0.33.0b5 at https://syn.example.com has no GET /executions/{execution_id}/session-inventory; this server predates the feature. Upgrade the server to use this command.
```

If the server cannot report its version either, the error says that instead of
naming a release. A 404 for a missing item, such as an unknown execution ID, is
unaffected and still reports the server's own message.