Credo checks that catch AI-generated code slop in Elixir.
23 checks for patterns that LLMs produce but experienced Elixir developers don't — blanket rescues, narrator docs, obvious comments, anti-idiomatic Enum usage, try/rescue around non-raising functions, N+1 queries, and more.
None of these overlap with built-in Credo: Credo never inspects doc/comment
content, doesn't catch Ecto anti-patterns or identity passthrough, and its
MapInto / CaseTrivialMatches checks are disabled or deprecated.
Installation
Add to mix.exs:
def deps do
[
{:ex_slop, "~> 0.1", only: [:dev, :test], runtime: false}
]
endThen add the checks you want to your .credo.exs — just append to the
existing enabled list:
# .credo.exs
{ExSlop.Check.Warning.BlanketRescue, []},
{ExSlop.Check.Warning.RescueWithoutReraise, []},
{ExSlop.Check.Warning.RepoAllThenFilter, []},
{ExSlop.Check.Warning.QueryInEnumMap, []},
{ExSlop.Check.Warning.GenserverAsKvStore, []},
{ExSlop.Check.Refactor.FilterNil, []},
{ExSlop.Check.Refactor.RejectNil, []},
{ExSlop.Check.Refactor.ReduceAsMap, []},
{ExSlop.Check.Refactor.MapIntoLiteral, []},
{ExSlop.Check.Refactor.IdentityPassthrough, []},
{ExSlop.Check.Refactor.IdentityMap, []},
{ExSlop.Check.Refactor.CaseTrueFalse, []},
{ExSlop.Check.Refactor.TryRescueWithSafeAlternative, []},
{ExSlop.Check.Refactor.WithIdentityElse, []},
{ExSlop.Check.Refactor.WithIdentityDo, []},
{ExSlop.Check.Refactor.SortThenReverse, []},
{ExSlop.Check.Refactor.StringConcatInReduce, []},
{ExSlop.Check.Readability.NarratorDoc, []},
{ExSlop.Check.Readability.DocFalseOnPublicFunction, []},
{ExSlop.Check.Readability.BoilerplateDocParams, []},
{ExSlop.Check.Readability.ObviousComment, []},
{ExSlop.Check.Readability.StepComment, []},
{ExSlop.Check.Readability.NarratorComment, []}Cherry-pick only the checks that make sense for your project.
Checks
Warnings
| Check | What it catches |
|---|---|
BlanketRescue | rescue _ -> nil or rescue _e -> {:error, "..."} |
RescueWithoutReraise | rescue e -> Logger.error(...); :error — logs but swallows |
RepoAllThenFilter | Repo.all(User) |> Enum.filter(& &1.active) — filter in SQL |
QueryInEnumMap | Enum.map(users, fn u -> Repo.get(...) end) — N+1 query |
GenserverAsKvStore | GenServer that's just Map.get/Map.put on state — use ETS or Agent |
Refactoring
| Check | Bad | Good |
|---|---|---|
FilterNil | Enum.filter(fn x -> x != nil end) | Enum.reject(&is_nil/1) |
RejectNil | Enum.reject(fn x -> x == nil end) | Enum.reject(&is_nil/1) |
ReduceAsMap | Enum.reduce([], fn x, acc -> [f(x) | acc] end) | Enum.map(&f/1) |
MapIntoLiteral | Enum.map(...) |> Enum.into(%{}) | Map.new(...) |
IdentityPassthrough | case r do {:ok, v} -> {:ok, v}; {:error, e} -> {:error, e} end | r |
IdentityMap | Enum.map(fn x -> x end) | remove the call |
CaseTrueFalse | case flag do true -> a; false -> b end | if flag, do: a, else: b |
TryRescueWithSafeAlternative | try do String.to_integer(x) rescue _ -> nil end | Integer.parse(x) |
WithIdentityElse | with {:ok, v} <- f() do v else {:error, r} -> {:error, r} end | drop the else |
WithIdentityDo | with {:ok, v} <- f() do {:ok, v} end | f() |
SortThenReverse | Enum.sort() |> Enum.reverse() | Enum.sort(:desc) |
StringConcatInReduce | Enum.reduce("", fn x, acc -> acc <> x end) | Enum.join/1 or IO data |
Readability
| Check | What it catches |
|---|---|
NarratorDoc | @moduledoc "This module provides functionality for..." |
DocFalseOnPublicFunction | Multiple @doc false on def in one module — cargo-culted |
BoilerplateDocParams | ## Parameters\n- conn: The connection struct |
ObviousComment | # Fetch the user above Repo.get(User, id) |
StepComment | # Step 1: Validate input |
NarratorComment | # Here we fetch the user / # Now we validate / # Let's create |