diff --git a/src/lib/model/fixtures/dimensionlab.ts b/src/lib/model/fixtures/dimensionlab.ts
index 316e9a8..572067f 100644
--- a/src/lib/model/fixtures/dimensionlab.ts
+++ b/src/lib/model/fixtures/dimensionlab.ts
@@ -44,7 +44,7 @@ export const dimensionLabDashboardFixture: DashboardDocument = {
     metric("system-disk-peak", "System Disk Peak", "percent", 49, "linux /boot", "ok"),
     metric("peak-cpu-busy", "Peak CPU Busy", "percent", 3, "linux-infra", "ok"),
     metric("top-cpu-container", "Top CPU Container", "percent", 7.9, "container placeholder", "ok"),
-    metric("top-ram-container", "Top RAM Container", "bytes", "5.2 GB", "container placeholder", "danger"),
+    metric("top-ram-container", "Top RAM Container", "bytes", 5.2 * 1024 ** 3, "container placeholder", "danger"),
     metric("gpu-3060-load", "3060 GPU Load", "percent", 0, "RTX 3060", "ok"),
     metric("gpu-3060-vram", "3060 VRAM", "percent", 0, "RTX 3060", "ok"),
     metric("gpu-3060-temp", "3060 Temp", "temperature", 54, "RTX 3060", "ok"),
@@ -111,14 +111,14 @@ export const dimensionLabDashboardFixture: DashboardDocument = {
   ],
 };
 
-type ValueKind = "percent" | "bytes" | "temperature" | "latency" | "number" | "text";
+type NumericValueKind = "percent" | "bytes" | "temperature" | "latency" | "number";
 type Severity = "neutral" | "ok" | "warning" | "danger" | "stale" | "unavailable";
 
 function metric(
   id: string,
   label: string,
-  kind: ValueKind,
-  value: number | string,
+  kind: NumericValueKind,
+  value: number,
   detail: string,
   severity: Severity,
 ) {
diff --git a/src/lib/model/schema.test.ts b/src/lib/model/schema.test.ts
index 40f9baa..0f3153b 100644
--- a/src/lib/model/schema.test.ts
+++ b/src/lib/model/schema.test.ts
@@ -54,6 +54,77 @@ describe("dashboard model validation", () => {
     }
   });
 
+  it("includes offending additional property names in errors", () => {
+    const invalid = JSON.parse(JSON.stringify(genericDashboardFixture));
+    invalid.metadata.unexpected = true;
+
+    const result = validateDashboardDocument(invalid);
+
+    expect(result.valid).toBe(false);
+    if (!result.valid) {
+      expect(result.errors.join(" ")).toContain("unexpected");
+    }
+  });
+
+  it("rejects non-finite numbers that cannot roundtrip through JSON", () => {
+    const invalid = JSON.parse(JSON.stringify(genericDashboardFixture));
+    invalid.telemetry[0].value.value = Number.NaN;
+
+    const result = validateDashboardDocument(invalid);
+
+    expect(result.valid).toBe(false);
+    if (!result.valid) {
+      expect(result.errors.join(" ")).toContain("finite JSON number");
+    }
+  });
+
+  it("rejects dangling layout references", () => {
+    const invalid = JSON.parse(JSON.stringify(genericDashboardFixture));
+    invalid.layout.telemetry.push("missing-card");
+
+    const result = validateDashboardDocument(invalid);
+
+    expect(result.valid).toBe(false);
+    if (!result.valid) {
+      expect(result.errors.join(" ")).toContain("missing-card");
+      expect(result.errors.join(" ")).toContain("must reference an existing item");
+    }
+  });
+
+  it("rejects duplicate IDs within collections", () => {
+    const invalid = JSON.parse(JSON.stringify(genericDashboardFixture));
+    invalid.telemetry[1].id = invalid.telemetry[0].id;
+
+    const result = validateDashboardDocument(invalid);
+
+    expect(result.valid).toBe(false);
+    if (!result.valid) {
+      expect(result.errors.join(" ")).toContain("must be unique");
+      expect(result.errors.join(" ")).toContain(invalid.telemetry[0].id);
+    }
+  });
+
+  it("rejects string values for numeric metric kinds", () => {
+    const invalid = JSON.parse(JSON.stringify(genericDashboardFixture));
+    invalid.telemetry[0].value.value = "not a percent";
+
+    const result = validateDashboardDocument(invalid);
+
+    expect(result.valid).toBe(false);
+  });
+
+  it("rejects contradictory warning and danger thresholds", () => {
+    const invalid = JSON.parse(JSON.stringify(genericDashboardFixture));
+    invalid.telemetry[0].thresholds = { warning: 90, danger: 80 };
+
+    const result = validateDashboardDocument(invalid);
+
+    expect(result.valid).toBe(false);
+    if (!result.valid) {
+      expect(result.errors.join(" ")).toContain("warning threshold");
+    }
+  });
+
   it("exports JSON Schema for external tool contracts", () => {
     expect(dashboardDocumentJsonSchema.$id).toContain("dashboard-document.v1");
     expect(dashboardDocumentJsonSchema.properties).toHaveProperty("schemaVersion");
diff --git a/src/lib/model/schema.ts b/src/lib/model/schema.ts
index 388e921..d338468 100644
--- a/src/lib/model/schema.ts
+++ b/src/lib/model/schema.ts
@@ -64,7 +64,7 @@ const DatasourceReferenceSchema = Type.Union([
   ExternalDatasourceSchema,
 ]);
 
-const MetricValueSchema = Type.Object(
+const NumericMetricValueSchema = Type.Object(
   {
     kind: Type.Union([
       Type.Literal("percent"),
@@ -72,21 +72,34 @@ const MetricValueSchema = Type.Object(
       Type.Literal("temperature"),
       Type.Literal("latency"),
       Type.Literal("number"),
-      Type.Literal("text"),
     ]),
-    value: Type.Union([Type.Number(), Type.String()]),
+    value: Type.Number(),
     unit: Type.Optional(Type.String({ minLength: 1 })),
     precision: Type.Optional(Type.Integer({ minimum: 0, maximum: 4 })),
   },
   { additionalProperties: false },
 );
 
+const TextMetricValueSchema = Type.Object(
+  {
+    kind: Type.Literal("text"),
+    value: Type.String(),
+    unit: Type.Optional(Type.String({ minLength: 1 })),
+  },
+  { additionalProperties: false },
+);
+
+const MetricValueSchema = Type.Union([
+  NumericMetricValueSchema,
+  TextMetricValueSchema,
+]);
+
 const ThresholdSchema = Type.Object(
   {
     warning: Type.Optional(Type.Number()),
     danger: Type.Optional(Type.Number()),
   },
-  { additionalProperties: false },
+  { additionalProperties: false, minProperties: 1 },
 );
 
 export const TelemetryCardSchema = Type.Object(
diff --git a/src/lib/model/validation.ts b/src/lib/model/validation.ts
index 2059f3c..3ed22ab 100644
--- a/src/lib/model/validation.ts
+++ b/src/lib/model/validation.ts
@@ -5,10 +5,20 @@ import {
   type DashboardDocument,
 } from "./schema";
 
+type DashboardValidationIssue = ErrorObject | SemanticValidationIssue;
+
+interface SemanticValidationIssue {
+  instancePath: string;
+  schemaPath: string;
+  keyword: "semantic";
+  params: Record<string, unknown>;
+  message: string;
+}
+
 export interface DashboardValidationFailure {
   valid: false;
   errors: string[];
-  details: ErrorObject[];
+  details: DashboardValidationIssue[];
 }
 
 export interface DashboardValidationSuccess {
@@ -24,27 +34,46 @@ const ajv = addFormats(
   new Ajv({
     allErrors: true,
     strict: false,
+    strictNumbers: true,
   }),
 );
 
 const validateDashboard = ajv.compile<DashboardDocument>(DashboardDocumentSchema);
 
-export function formatValidationErrors(errors: ErrorObject[] = []): string[] {
+export function formatValidationErrors(
+  errors: DashboardValidationIssue[] = [],
+): string[] {
   return errors.map((error) => {
     const path = error.instancePath || "/";
+    const suffix = formatErrorParams(error);
     const message = error.message || "is invalid";
-    return `${path} ${message}`;
+    return `${path} ${message}${suffix}`;
   });
 }
 
 export function validateDashboardDocument(
   value: unknown,
 ): DashboardValidationResult {
+  const finiteNumberIssues: SemanticValidationIssue[] = [];
+  collectFiniteNumberIssues(value, "", finiteNumberIssues);
+
   if (validateDashboard(value)) {
-    return { valid: true, data: value };
+    const semanticIssues = [
+      ...finiteNumberIssues,
+      ...validateSemanticRules(value),
+    ];
+    if (semanticIssues.length === 0) {
+      return { valid: true, data: value };
+    }
+
+    return {
+      valid: false,
+      errors: formatValidationErrors(semanticIssues),
+      details: semanticIssues,
+    };
   }
 
-  const details = [...(validateDashboard.errors || [])];
+  const details = [...(validateDashboard.errors || []), ...finiteNumberIssues];
   return {
     valid: false,
     errors: formatValidationErrors(details),
@@ -64,3 +93,165 @@ export function assertDashboardDocument(
 export function isDashboardDocument(value: unknown): value is DashboardDocument {
   return validateDashboardDocument(value).valid;
 }
+
+function formatErrorParams(error: DashboardValidationIssue): string {
+  if (error.keyword === "additionalProperties") {
+    const additionalProperty = error.params.additionalProperty;
+    return typeof additionalProperty === "string"
+      ? `: ${additionalProperty}`
+      : "";
+  }
+
+  if (error.keyword === "semantic") {
+    const id = error.params.id;
+    const ref = error.params.ref;
+    if (typeof id === "string") return `: ${id}`;
+    if (typeof ref === "string") return `: ${ref}`;
+  }
+
+  return "";
+}
+
+function validateSemanticRules(document: DashboardDocument): SemanticValidationIssue[] {
+  const issues: SemanticValidationIssue[] = [];
+
+  collectDuplicateIdIssues("telemetry", document.telemetry, issues);
+  collectDuplicateIdIssues("serviceGroups", document.serviceGroups, issues);
+  collectDuplicateIdIssues("statusStrips", document.statusStrips, issues);
+  collectDuplicateIdIssues("modules", document.modules || [], issues);
+
+  document.serviceGroups.forEach((group, groupIndex) => {
+    collectDuplicateIdIssues(
+      `serviceGroups/${groupIndex}/services`,
+      group.services,
+      issues,
+    );
+  });
+
+  collectMissingReferenceIssues(
+    "layout/telemetry",
+    document.layout.telemetry,
+    new Set(document.telemetry.map((item) => item.id)),
+    issues,
+  );
+  collectMissingReferenceIssues(
+    "layout/serviceGroups",
+    document.layout.serviceGroups,
+    new Set(document.serviceGroups.map((item) => item.id)),
+    issues,
+  );
+  collectMissingReferenceIssues(
+    "layout/statusStrips",
+    document.layout.statusStrips,
+    new Set(document.statusStrips.map((item) => item.id)),
+    issues,
+  );
+  collectMissingReferenceIssues(
+    "layout/modules",
+    document.layout.modules || [],
+    new Set((document.modules || []).map((item) => item.id)),
+    issues,
+  );
+
+  document.telemetry.forEach((card, index) => {
+    const warning = card.thresholds?.warning;
+    const danger = card.thresholds?.danger;
+    if (warning !== undefined && danger !== undefined && warning > danger) {
+      issues.push(
+        semanticIssue(
+          `/telemetry/${index}/thresholds`,
+          "warning threshold must be less than or equal to danger threshold",
+          { id: card.id },
+        ),
+      );
+    }
+  });
+
+  return issues;
+}
+
+function collectFiniteNumberIssues(
+  value: unknown,
+  path: string,
+  issues: SemanticValidationIssue[],
+) {
+  if (typeof value === "number") {
+    if (!Number.isFinite(value)) {
+      issues.push(
+        semanticIssue(path || "/", "must be a finite JSON number", {}),
+      );
+    }
+    return;
+  }
+
+  if (Array.isArray(value)) {
+    value.forEach((item, index) => {
+      collectFiniteNumberIssues(item, `${path}/${index}`, issues);
+    });
+    return;
+  }
+
+  if (value && typeof value === "object") {
+    Object.entries(value).forEach(([key, item]) => {
+      collectFiniteNumberIssues(item, `${path}/${escapeJsonPointer(key)}`, issues);
+    });
+  }
+}
+
+function collectDuplicateIdIssues(
+  collectionPath: string,
+  items: Array<{ id: string }>,
+  issues: SemanticValidationIssue[],
+) {
+  const seen = new Set<string>();
+  items.forEach((item, index) => {
+    if (seen.has(item.id)) {
+      issues.push(
+        semanticIssue(
+          `/${collectionPath}/${index}/id`,
+          "must be unique within its collection",
+          { id: item.id },
+        ),
+      );
+      return;
+    }
+    seen.add(item.id);
+  });
+}
+
+function collectMissingReferenceIssues(
+  layoutPath: string,
+  refs: string[],
+  validIds: Set<string>,
+  issues: SemanticValidationIssue[],
+) {
+  refs.forEach((ref, index) => {
+    if (!validIds.has(ref)) {
+      issues.push(
+        semanticIssue(
+          `/${layoutPath}/${index}`,
+          "must reference an existing item",
+          { ref },
+        ),
+      );
+    }
+  });
+}
+
+function semanticIssue(
+  instancePath: string,
+  message: string,
+  params: Record<string, unknown>,
+): SemanticValidationIssue {
+  return {
+    instancePath,
+    schemaPath: "",
+    keyword: "semantic",
+    params,
+    message,
+  };
+}
+
+function escapeJsonPointer(value: string): string {
+  return value.replaceAll("~", "~0").replaceAll("/", "~1");
+}