> For the complete documentation index, see [llms.txt](https://osl.mistium.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://osl.mistium.com/operators/mathematical-usage/addition-operator-+.md).

# Addition (+)

Use `+` to add two numbers. Both operands must be numbers; OSL reports a compile-time type error when it can prove they are incompatible, and checks dynamic (`any`) values at runtime.

```javascript
log 10 + 5
// does an addition on its two operands and returns 15
// this is doing 10 plus 5
```

Two strings can also be joined with `+`, but `+` does not convert mixed types:

```javascript
log "hello" + "world" // "helloworld"
log "count: " + 5      // TypeError
log "count: " ++ 5     // "count: 5"
```