Elixir New Added 12 September 2026

Elixir: (KeyError) key :name not found in: %{"name" => "ada"}

Dot access and `Map.fetch!/2` raise rather than returning nil when a key is missing, and the usual cause is string keys where atom keys were expected. A map decoded from JSON has `"name"`, not `:name`, and the two are different keys in the same map.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix

# The message prints the map, so read which key style it actually has
params["name"]          # string keys: bracket access, returns nil if absent
params.name             # atom keys only, raises when missing
Map.get(params, :name, "default")

# Decode straight into atoms only for input you control: atoms are never
# garbage collected, so this is a denial of service risk on user input
Jason.decode!(body, keys: :atoms!)   # only pre-existing atoms, safer

# In Phoenix, let the changeset do the conversion instead
Structs.changeset(%User{}, params) |> Ecto.Changeset.apply_changes()

# A struct raises the same way for a field that does not exist,
# which is a typo rather than missing data
iex> %User{}.nmae

How to diagnose Elixir errors

Elixir errors are shaped by the actor model: a GenServer.call timeout does not mean the server crashed, it means the server was busy for longer than the caller was willing to wait. The right question is usually "what is that process doing?" rather than "why did the call fail?". Because supervisors restart failed processes automatically, transient errors can also hide in the logs while the system appears healthy.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

Attach to a running node with iex --remsh and inspect the process: Process.info(pid, :message_queue_len). A growing mailbox means the process is the bottleneck.
Use :observer.start() to see the supervision tree, process memory and message queues visually.
Move long-running work out of handle_call. Use handle_cast, a Task, or a dedicated pool so the GenServer stays responsive.
Check restart intensity. A supervisor that exceeds max_restarts takes down its own supervisor, producing a cascade that looks like an unrelated failure at the top.
For compile errors in dependencies, run mix deps.compile --force and check that any required native toolchain (make, gcc, erlang headers) is installed.

Tools worth reaching for

:observer.start()
iex --remsh
Process.info/2
mix deps.tree
:recon

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

hexdocs.pm

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