Error: Invalid default value for variable: default does not match the type constraint

TL;DR

The default in your variable block does not satisfy the type you declared. Terraform checks this at validate time, before any plan. Change the default to a value of the declared type (or loosen the type), then terraform validate.

The error

Error: Invalid default value for variable

  on variables.tf line 5, in variable "tags":
   5:   default = "none"

This default value is not compatible with the variable's type constraint:
map of string required.

Steps to fix

1. Open the variable block the error names. Read the type line and the default line together.

• Expected: you see the mismatch (string default vs map(string) type).

1. Decide which side is wrong. If callers pass maps, fix the default: default = {}. If the variable really is a string, fix the type: type = string.

• Expected: default is a valid value of the declared type.

1. Run terraform validate.

• Expected: Success! The configuration is valid.

When to use this

• terraform validate fails with Invalid default value for variable right after you added or edited a variable's type or default.

When NOT to use this

• Invalid value for variable (without "default") means a caller-supplied value failed validation, not the default. Invalid function argument is a function call problem.

Compatibility

• Terraform 0.12+ type system; the check runs in validate, plan, and apply across all 1.x versions.

Root cause

Variable defaults are validated against the type constraint when the configuration loads, independent of any input. A default that cannot convert to the declared type is a configuration bug, so Terraform fails fast instead of waiting for someone to omit the variable.

Edge cases

• default = null is allowed for any type unless nullable = false is set.
• An empty tuple [] is not a valid map(string); use {}.
• any as the type skips this check entirely, but you lose validation for caller-supplied values too.