Error: Missing newline after argument: HCL syntax error on one line

Not specified by the original author.

TL;DR

Two arguments ended up on one line, or you used non-HCL syntax (like a JavaScript function call) inside a .tf file. HCL wants one argument per line. Split them, replace JS-isms with HCL natives (jsonencode), and run terraform fmt.

The error

Error: Missing newline after argument

  on main.tf line 200:
  200: event_pattern = JSON.stringify({

Steps to fix

1. Open the flagged line. Look for two arguments jammed together, or a function call from another language (JSON.stringify, etc.).

   • Expected: you spot the offending syntax.

2. Rewrite in HCL: one argument per line, HCL-native functions:

   event_pattern = jsonencode({
     source = ["my.service"]
   })

   • Expected: no foreign syntax remains.

3. Run terraform fmt then terraform validate.

   • Expected: Success! The configuration is valid.

When to use this

• terraform validate/plan fails with Missing newline after argument after editing or pasting config, especially config translated from another language.

When NOT to use this

• Invalid character (e.g. ;) is the sibling error for characters HCL rejects outright. If the line looks fine, check for invisible characters from copy-paste.

Compatibility

• All Terraform versions; HCL2 syntax rules are stable.

Root cause

HCL separates block arguments with newlines. Pasting multi-argument snippets onto one line, or transliterating JavaScript/Python expressions directly into .tf files, produces tokens the parser cannot split into separate arguments.

Edge cases

• Heredocs (<<EOT) containing code from other languages are fine; the error only applies to HCL outside strings.
• terraform fmt will not fix this; it only formats valid syntax. Fix the syntax first, then format.

The yatricloud AI demo troubleshooting guide documents this exact syntax error: "Error: Missing newline after argument" on a line like event_pattern = JSON.stringify({, with the fix that HCL does not support JavaScript functions and the correct form uses jsonencode() instead. The guide pairs it with the inconsistent-lock-file and no-configuration-files errors in the same Terraform Errors section, showing it as one of the routine syntax failures in real projects.

Not specified by the original author.

TL;DR

HCL does not use semicolons. If you wrote variable "x" { type = string; default = "y" } on one line, Terraform rejects the ;. Put each argument on its own line and the error goes away.

The error

Error: Invalid character
The ";" character is not valid. Use newlines to separate arguments and blocks

Steps to fix

1. Open the file and line the error names. Look for ; separating arguments on one line.

   • Expected: you find the single-line block with semicolons.

2. Expand it to one argument per line:

   variable "common_tags" {
     type    = map(string)
     default = {}
   }

   • Expected: no semicolons remain in the block.

3. Run terraform fmt to normalize the file, then terraform validate.

   • Expected: Success! The configuration is valid.

When to use this

• terraform validate/plan fails with Invalid character pointing at ;, backticks pasted from markdown, or other stray characters, right after writing or pasting config.

When NOT to use this

• Missing newline after argument is the sibling syntax error (different message). If the invalid character is invisible, suspect smart quotes or zero-width characters from copy-paste and retype the line.

Compatibility

• All Terraform versions; HCL syntax rules are stable.

Root cause

HCL's native syntax separates block arguments with newlines, not semicolons. People coming from JSON, Python, or C-style languages write one-line blocks with ; separators out of habit, and the HCL parser rejects the character outright.

Edge cases

• Backticks accidentally pasted from markdown code fences produce the same error naming the backtick character; rewrite the file from the terminal to be safe.
• $var.name without braces (shell-style) is a different error (Invalid character naming $); use ${var.name} inside quotes.
• terraform fmt fixes indentation but does not remove semicolons; you must edit them out.

A real project troubleshooting log records hitting this 3+ times across modules: "Error: Invalid character. The \";\" character is not valid. Use newlines to separate arguments and blocks". The root cause was single-line variable blocks like variable "common_tags" { type = map(string); default = {} }, which HCL forbids. The fix was to always expand variable blocks to multi-line format, with the rule "never put semicolons in HCL." A separate Medium walkthrough shows the same error from backticks accidentally pasted from markdown into a .tf file.

Not specified by the original author.

TL;DR: You put an argument on the same line as the block's opening brace without closing it on the same line. HCL treats that as a single-line block definition, which must open AND close on one line. Either close it there or move the argument to its own line.

Error: Invalid single-argument block definition

  on terragrunt.hcl line 1, in terraform:

   1: terraform { source = "./mod"

   2: inputs = { a = }

An argument definition on the same line as its containing block creates a
single-line block definition, which must also be closed on the same line.

Steps

1. Run terragrunt hcl validate. Expected: it points at the exact line (better than guessing).

2. Fix the block: either close it on the same line (terraform { source = "./mod" }) or put the argument on its own line inside a multi-line block. Expected: braces balance.

3. Run terragrunt hcl fmt --check --diff for formatting. Expected: clean.

4. Re-run your command. Expected: the parse error is gone.

When this applies

• Invalid single-argument block definition naming a block with an argument on the opening line.
• Any HCL syntax error in terragrunt.hcl / root.hcl: the validator path is the same.

When it doesn't apply

• The file parses but a VALUE is wrong (unknown attribute, type mismatch): those are evaluation errors; terragrunt render shows the resolved config.
• ${...} inside a generate heredoc being eaten by Terragrunt: that's the generate-template trap (escape as $${...}), not a syntax error.

Tool versions

All Terragrunt versions (HCL syntax).

Why it happens

HCL has two block forms: single-line (block { arg = x }) and multi-line. An argument on the opening line selects the single-line form, so a missing closing brace on that line is a syntax error, not just bad style.

Edge cases

• Two Terragrunt-specific traps that LOOK like generic HCL errors: values.* unbound outside a generated unit (validate the materialized unit after terragrunt stack generate, not the catalog source), and ${...} in generate heredocs evaluated by Terragrunt instead of passed through.

Asked: how to fix Error: Invalid single-argument block definition. Verified answer: Fixes Terragrunt's 'Error: Invalid single-argument block definition' by closing single-line blocks on the same line. The fix steps above were cross-checked against the accepted community answer at https://github.com/kevin-burns/claude-skills/blob/HEAD/terragrunt-skill/references/error-patterns.md, which confirms the same resolution.