> ## Documentation Index
> Fetch the complete documentation index at: https://tally.wharflab.com/llms.txt
> Use this file to discover all available pages before exploring further.

# tally/unknown-instruction

> Detects misspelled or invalid Dockerfile instruction keywords.

Detects misspelled or invalid Dockerfile instruction keywords.

| Property | Value                                |
| -------- | ------------------------------------ |
| Severity | Error                                |
| Category | Correctness                          |
| Default  | Enabled                              |
| Type     | Fail-fast syntax check (exit code 4) |

## Description

Dockerfile instructions must be one of the keywords recognized by BuildKit
(`FROM`, `RUN`, `COPY`, `ADD`, `WORKDIR`, `ENV`, `ARG`, `EXPOSE`, `LABEL`,
`CMD`, `ENTRYPOINT`, `VOLUME`, `USER`, `SHELL`, `HEALTHCHECK`, `ONBUILD`,
`STOPSIGNAL`, `MAINTAINER`).

A misspelled keyword (e.g., `FORM`, `COPPY`, `WROKDIR`) is silently treated as
a comment by the parser, making the resulting image incorrect without any
obvious error. This check catches typos early using Levenshtein distance and
suggests the closest valid instruction when within edit distance 2.

This is a fail-fast check: if any unknown instruction is found, linting aborts
with exit code 4.

## Examples

### Bad

```dockerfile theme={null}
FORM alpine:3.20
RUN echo "hello"
```

Output:

```text theme={null}
Error: Dockerfile:1: unknown instruction "FORM" (did you mean "FROM"?)
```

### Good

```dockerfile theme={null}
FROM alpine:3.20
RUN echo "hello"
```