diff --git a/src/Describable.php b/src/Describable.php
new file mode 100644
index 0000000..49d4ded
--- /dev/null
+++ b/src/Describable.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Superscript\Axiom;
+
+interface Describable
+{
+    /**
+     * Return a human-readable description of this source,
+     * suitable for textualising the source tree for AI consumption.
+     */
+    public function describe(): string;
+}
diff --git a/src/Sources/InfixExpression.php b/src/Sources/InfixExpression.php
index ac68e46..739b351 100644
--- a/src/Sources/InfixExpression.php
+++ b/src/Sources/InfixExpression.php
@@ -4,13 +4,35 @@
 
 namespace Superscript\Axiom\Sources;
 
+use Superscript\Axiom\Describable;
 use Superscript\Axiom\Source;
 
-final readonly class InfixExpression implements Source
+final readonly class InfixExpression implements Source, Describable
 {
     public function __construct(
         public Source $left,
         public string $operator,
         public Source $right,
     ) {}
+
+    public function describe(): string
+    {
+        $left = $this->describeOperand($this->left);
+        $right = $this->describeOperand($this->right);
+
+        return sprintf('%s %s %s', $left, $this->operator, $right);
+    }
+
+    private function describeOperand(Source $source): string
+    {
+        $description = $source instanceof Describable
+            ? $source->describe()
+            : (new \ReflectionClass($source))->getShortName();
+
+        if ($source instanceof self) {
+            return sprintf('(%s)', $description);
+        }
+
+        return $description;
+    }
 }
diff --git a/src/Sources/StaticSource.php b/src/Sources/StaticSource.php
index 85866c6..d7ea596 100644
--- a/src/Sources/StaticSource.php
+++ b/src/Sources/StaticSource.php
@@ -4,11 +4,18 @@
 
 namespace Superscript\Axiom\Sources;
 
+use SebastianBergmann\Exporter\Exporter;
+use Superscript\Axiom\Describable;
 use Superscript\Axiom\Source;
 
-final readonly class StaticSource implements Source
+final readonly class StaticSource implements Source, Describable
 {
     public function __construct(
         public mixed $value,
     ) {}
+
+    public function describe(): string
+    {
+        return (new Exporter())->shortenedExport($this->value);
+    }
 }
diff --git a/src/Sources/SymbolSource.php b/src/Sources/SymbolSource.php
index f98eb8e..380e7d7 100644
--- a/src/Sources/SymbolSource.php
+++ b/src/Sources/SymbolSource.php
@@ -4,12 +4,20 @@
 
 namespace Superscript\Axiom\Sources;
 
+use Superscript\Axiom\Describable;
 use Superscript\Axiom\Source;
 
-final readonly class SymbolSource implements Source
+final readonly class SymbolSource implements Source, Describable
 {
     public function __construct(
         public string $name,
         public ?string $namespace = null,
     ) {}
+
+    public function describe(): string
+    {
+        return $this->namespace !== null
+            ? sprintf('%s.%s', $this->namespace, $this->name)
+            : $this->name;
+    }
 }
diff --git a/src/Sources/TypeDefinition.php b/src/Sources/TypeDefinition.php
index fcb4832..9290386 100644
--- a/src/Sources/TypeDefinition.php
+++ b/src/Sources/TypeDefinition.php
@@ -4,13 +4,25 @@
 
 namespace Superscript\Axiom\Sources;
 
+use Superscript\Axiom\Describable;
 use Superscript\Axiom\Source;
 use Superscript\Axiom\Types\Type;
 
-final readonly class TypeDefinition implements Source
+final readonly class TypeDefinition implements Source, Describable
 {
     public function __construct(
         public Type $type,
         public Source $source,
     ) {}
+
+    public function describe(): string
+    {
+        $shortName = (new \ReflectionClass($this->type))->getShortName();
+        $typeName = lcfirst(str_ends_with($shortName, 'Type') ? substr($shortName, 0, -4) : $shortName);
+        $sourceDescription = $this->source instanceof Describable
+            ? $this->source->describe()
+            : (new \ReflectionClass($this->source))->getShortName();
+
+        return sprintf('%s (as %s)', $sourceDescription, $typeName);
+    }
 }
diff --git a/src/Sources/UnaryExpression.php b/src/Sources/UnaryExpression.php
index 2769d97..618b599 100644
--- a/src/Sources/UnaryExpression.php
+++ b/src/Sources/UnaryExpression.php
@@ -1,14 +1,25 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Superscript\Axiom\Sources;
 
+use Superscript\Axiom\Describable;
 use Superscript\Axiom\Source;
 
-final readonly class UnaryExpression implements Source
+final readonly class UnaryExpression implements Source, Describable
 {
     public function __construct(
         public string $operator,
         public Source $operand,
-    ) {
+    ) {}
+
+    public function describe(): string
+    {
+        $operand = $this->operand instanceof Describable
+            ? $this->operand->describe()
+            : (new \ReflectionClass($this->operand))->getShortName();
+
+        return sprintf('%s%s', $this->operator, $operand);
     }
-}
\ No newline at end of file
+}
diff --git a/tests/Sources/DescribableTest.php b/tests/Sources/DescribableTest.php
new file mode 100644
index 0000000..6af7ced
--- /dev/null
+++ b/tests/Sources/DescribableTest.php
@@ -0,0 +1,244 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Superscript\Axiom\Tests\Sources;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\Attributes\UsesClass;
+use PHPUnit\Framework\TestCase;
+use Superscript\Axiom\Source;
+use Superscript\Axiom\Sources\InfixExpression;
+use Superscript\Axiom\Sources\StaticSource;
+use Superscript\Axiom\Sources\SymbolSource;
+use Superscript\Axiom\Sources\TypeDefinition;
+use Superscript\Axiom\Sources\UnaryExpression;
+use Superscript\Axiom\Types\BooleanType;
+use Superscript\Axiom\Types\ListType;
+use Superscript\Axiom\Types\NumberType;
+use Superscript\Axiom\Types\StringType;
+
+#[CoversClass(StaticSource::class)]
+#[CoversClass(SymbolSource::class)]
+#[CoversClass(TypeDefinition::class)]
+#[CoversClass(InfixExpression::class)]
+#[CoversClass(UnaryExpression::class)]
+#[UsesClass(NumberType::class)]
+#[UsesClass(StringType::class)]
+#[UsesClass(BooleanType::class)]
+#[UsesClass(ListType::class)]
+class DescribableTest extends TestCase
+{
+    #[Test]
+    public function static_source_describes_string_value(): void
+    {
+        $source = new StaticSource('hello');
+        $this->assertSame("'hello'", $source->describe());
+    }
+
+    #[Test]
+    public function static_source_describes_integer_value(): void
+    {
+        $source = new StaticSource(42);
+        $this->assertSame('42', $source->describe());
+    }
+
+    #[Test]
+    public function static_source_describes_null_value(): void
+    {
+        $source = new StaticSource(null);
+        $this->assertSame('null', $source->describe());
+    }
+
+    #[Test]
+    public function static_source_describes_boolean_value(): void
+    {
+        $source = new StaticSource(true);
+        $this->assertSame('true', $source->describe());
+    }
+
+    #[Test]
+    public function symbol_source_describes_name(): void
+    {
+        $source = new SymbolSource('price');
+        $this->assertSame('price', $source->describe());
+    }
+
+    #[Test]
+    public function symbol_source_describes_namespaced_name(): void
+    {
+        $source = new SymbolSource('pi', 'math');
+        $this->assertSame('math.pi', $source->describe());
+    }
+
+    #[Test]
+    public function type_definition_describes_as_type(): void
+    {
+        $source = new TypeDefinition(new NumberType(), new SymbolSource('price'));
+        $this->assertSame('price (as number)', $source->describe());
+    }
+
+    #[Test]
+    public function type_definition_describes_string_type(): void
+    {
+        $source = new TypeDefinition(new StringType(), new StaticSource('hello'));
+        $this->assertSame("'hello' (as string)", $source->describe());
+    }
+
+    #[Test]
+    public function type_definition_describes_boolean_type(): void
+    {
+        $source = new TypeDefinition(new BooleanType(), new SymbolSource('active'));
+        $this->assertSame('active (as boolean)', $source->describe());
+    }
+
+    #[Test]
+    public function type_definition_describes_list_type(): void
+    {
+        $source = new TypeDefinition(new ListType(new NumberType()), new SymbolSource('values'));
+        $this->assertSame('values (as list)', $source->describe());
+    }
+
+    #[Test]
+    public function type_definition_with_non_describable_source_falls_back_to_class_name(): void
+    {
+        $anonymous = new class implements Source {};
+
+        $source = new TypeDefinition(new NumberType(), $anonymous);
+
+        $description = $source->describe();
+        $this->assertStringEndsWith('(as number)', $description);
+    }
+
+    #[Test]
+    public function infix_expression_describes_operation(): void
+    {
+        $source = new InfixExpression(
+            new StaticSource(1),
+            '+',
+            new StaticSource(2),
+        );
+        $this->assertSame('1 + 2', $source->describe());
+    }
+
+    #[Test]
+    public function infix_expression_describes_comparison(): void
+    {
+        $source = new InfixExpression(
+            new SymbolSource('age'),
+            '>=',
+            new StaticSource(18),
+        );
+        $this->assertSame('age >= 18', $source->describe());
+    }
+
+    #[Test]
+    public function infix_expression_describes_custom_operator(): void
+    {
+        $source = new InfixExpression(
+            new SymbolSource('tags'),
+            'has',
+            new StaticSource('featured'),
+        );
+        $this->assertSame("tags has 'featured'", $source->describe());
+    }
+
+    #[Test]
+    public function infix_expression_wraps_nested_infix_in_parentheses(): void
+    {
+        $source = new InfixExpression(
+            new SymbolSource('price'),
+            '*',
+            new InfixExpression(
+                new StaticSource(1),
+                '-',
+                new SymbolSource('discount'),
+            ),
+        );
+        $this->assertSame(
+            'price * (1 - discount)',
+            $source->describe(),
+        );
+    }
+
+    #[Test]
+    public function infix_with_non_describable_left_falls_back_to_class_name(): void
+    {
+        $anonymous = new class implements Source {};
+
+        $source = new InfixExpression(
+            $anonymous,
+            '+',
+            new StaticSource(1),
+        );
+
+        $description = $source->describe();
+        $this->assertStringEndsWith('+ 1', $description);
+    }
+
+    #[Test]
+    public function infix_with_non_describable_right_falls_back_to_class_name(): void
+    {
+        $anonymous = new class implements Source {};
+
+        $source = new InfixExpression(
+            new StaticSource(1),
+            '+',
+            $anonymous,
+        );
+
+        $description = $source->describe();
+        $this->assertStringStartsWith('1 + ', $description);
+    }
+
+    #[Test]
+    public function unary_expression_describes_negation(): void
+    {
+        $source = new UnaryExpression('!', new SymbolSource('active'));
+        $this->assertSame('!active', $source->describe());
+    }
+
+    #[Test]
+    public function unary_expression_describes_negative(): void
+    {
+        $source = new UnaryExpression('-', new StaticSource(5));
+        $this->assertSame('-5', $source->describe());
+    }
+
+    #[Test]
+    public function unary_with_non_describable_source_falls_back_to_class_name(): void
+    {
+        $anonymous = new class implements Source {};
+
+        $source = new UnaryExpression('!', $anonymous);
+
+        $description = $source->describe();
+        $this->assertStringStartsWith('!', $description);
+    }
+
+    #[Test]
+    public function complex_nested_expression(): void
+    {
+        $source = new InfixExpression(
+            new TypeDefinition(
+                new NumberType(),
+                new SymbolSource('price'),
+            ),
+            '*',
+            new InfixExpression(
+                new StaticSource(1),
+                '-',
+                new TypeDefinition(
+                    new NumberType(),
+                    new SymbolSource('discount', 'rates'),
+                ),
+            ),
+        );
+
+        $this->assertSame(
+            'price (as number) * (1 - rates.discount (as number))',
+            $source->describe(),
+        );
+    }
+}