diff --git a/src/observations/dto.ts b/src/observations/dto.ts
new file mode 100644
index 0000000..d6cdf02
--- /dev/null
+++ b/src/observations/dto.ts
@@ -0,0 +1,38 @@
+import { IsISO8601, IsNumber, IsOptional, IsString, Length, Max, Min } from 'class-validator';
+
+export class CreateObservationDto {
+  @IsString()
+  @Length(1, 64)
+  subjectType!: string;
+
+  @IsString()
+  @Length(1, 255)
+  subjectId!: string;
+
+  @IsString()
+  @Length(1, 128)
+  metric!: string;
+
+  @IsString()
+  @Length(1, 1000)
+  value!: string;
+
+  @IsOptional()
+  @IsString()
+  @Length(1, 32)
+  unit?: string;
+
+  @IsString()
+  @Length(1, 128)
+  source!: string;
+
+  @IsOptional()
+  @IsISO8601()
+  observedAt?: string;
+
+  @IsOptional()
+  @IsNumber()
+  @Min(0)
+  @Max(1)
+  confidence?: number;
+}