diff --git a/cmd/hcldec/spec-format.md b/cmd/hcldec/spec-format.md
index 2126d69..69b21b8 100644
--- a/cmd/hcldec/spec-format.md
+++ b/cmd/hcldec/spec-format.md
@@ -274,7 +274,8 @@ literal {
 
 `literal` spec blocks accept the following argument:
 
-* `value` (required) - The value to return.
+* `value` (required) - The value to return. This attribute may be an expression
+  that uses [functions](#functions).
 
 `literal` is a leaf spec type, so no nested spec blocks are permitted.
 
@@ -330,6 +331,30 @@ transform {
   spec. The variable `nested` is defined when evaluating this expression, with
   the result value of the nested spec.
 
+The `result` expression may use [functions](#functions).
+
+## Functions
+
+Certain expressions within a specification may use the following functions.
+The documentation for each spec type above specifies where functions may
+be used.
+
+* `abs(number)` returns the absolute (positive) value of the given number.
+* `coalesce(vals...)` returns the first non-null value given.
+* `concat(lists...)` concatenates together all of the given lists to produce a new list.
+* `hasindex(val, idx)` returns true if the expression `val[idx]` could succeed.
+* `int(number)` returns the integer portion of the given number, rounding towards zero.
+* `jsondecode(str)` interprets the given string as JSON and returns the resulting data structure.
+* `jsonencode(val)` returns a JSON-serialized version of the given value.
+* `length(collection)` returns the number of elements in the given collection (list, set, map, object, or tuple).
+* `lower(string)` returns the given string with all uppercase letters converted to lowercase.
+* `max(numbers...)` returns the greatest of the given numbers.
+* `min(numbers...)` returns the smallest of the given numbers.
+* `reverse(string)` returns the given string with all of the characters in reverse order.
+* `strlen(string)` returns the number of characters in the given string.
+* `substr(string, offset, length)` returns the requested substring of the given string.
+* `upper(string)` returns the given string with all lowercase letters converted to uppercase.
+
 ## Type Expressions
 
 Type expressions are used to describe the expected type of an attribute, as
diff --git a/cmd/hcldec/spec.go b/cmd/hcldec/spec.go
index fa09663..8010919 100644
--- a/cmd/hcldec/spec.go
+++ b/cmd/hcldec/spec.go
@@ -9,6 +9,10 @@ import (
 	"github.com/zclconf/go-cty/cty"
 )
 
+var specCtx = &hcl.EvalContext{
+	Functions: specFuncs,
+}
+
 func loadSpecFile(filename string) (hcldec.Spec, hcl.Diagnostics) {
 	file, diags := parser.ParseHCLFile(filename)
 	if diags.HasErrors() {
@@ -382,7 +386,7 @@ func decodeLiteralSpec(body hcl.Body) (hcldec.Spec, hcl.Diagnostics) {
 	}
 
 	var args content
-	diags := gohcl.DecodeBody(body, nil, &args)
+	diags := gohcl.DecodeBody(body, specCtx, &args)
 	if diags.HasErrors() {
 		return errSpec, diags
 	}
@@ -455,8 +459,9 @@ func decodeTransformSpec(body hcl.Body) (hcldec.Spec, hcl.Diagnostics) {
 	}
 
 	spec := &hcldec.TransformExprSpec{
-		Expr:    args.Result,
-		VarName: "nested",
+		Expr:         args.Result,
+		VarName:      "nested",
+		TransformCtx: specCtx,
 	}
 
 	nestedContent, nestedDiags := args.Nested.Content(specSchemaUnlabelled)
diff --git a/cmd/hcldec/spec_funcs.go b/cmd/hcldec/spec_funcs.go
new file mode 100644
index 0000000..99c8ea6
--- /dev/null
+++ b/cmd/hcldec/spec_funcs.go
@@ -0,0 +1,24 @@
+package main
+
+import (
+	"github.com/zclconf/go-cty/cty/function"
+	"github.com/zclconf/go-cty/cty/function/stdlib"
+)
+
+var specFuncs = map[string]function.Function{
+	"abs":        stdlib.AbsoluteFunc,
+	"coalesce":   stdlib.CoalesceFunc,
+	"concat":     stdlib.ConcatFunc,
+	"hasindex":   stdlib.HasIndexFunc,
+	"int":        stdlib.IntFunc,
+	"jsondecode": stdlib.JSONDecodeFunc,
+	"jsonencode": stdlib.JSONEncodeFunc,
+	"length":     stdlib.LengthFunc,
+	"lower":      stdlib.LowerFunc,
+	"max":        stdlib.MaxFunc,
+	"min":        stdlib.MinFunc,
+	"reverse":    stdlib.ReverseFunc,
+	"strlen":     stdlib.StrlenFunc,
+	"substr":     stdlib.SubstrFunc,
+	"upper":      stdlib.UpperFunc,
+}