diff --git a/src/er/request-validation.ts b/src/er/request-validation.ts
new file mode 100644
index 0000000..6bbe44c
--- /dev/null
+++ b/src/er/request-validation.ts
@@ -0,0 +1,110 @@
+import { SiaxError } from "../platform/errors";
+import type { ErCandidateRequest, ErRecord } from "./entity-resolution-service";
+
+function finiteThreshold(value: unknown, field: string, fallback: number): number {
+  if (value === undefined) return fallback;
+  const parsed = Number(value);
+  if (!Number.isFinite(parsed) || parsed < 0 || parsed > 1) {
+    throw new SiaxError("INVALID_REQUEST", "0pt.er", `${field} must be a finite number between 0 and 1`);
+  }
+  return parsed;
+}
+
+export function parseErCandidateRequest(raw: unknown): ErCandidateRequest {
+  if (!raw || typeof raw !== "object" || Array.isArray(raw)) {
+    throw new SiaxError("INVALID_REQUEST", "0pt.er", "JSON object body is required");
+  }
+  const body = raw as Record<string, unknown>;
+  const tenantId = typeof body.tenant_id === "string" ? body.tenant_id.trim() : "";
+  const projectId = typeof body.project_id === "string" ? body.project_id.trim() : "";
+  if (!tenantId) throw new SiaxError("INVALID_REQUEST", "0pt.er", "tenant_id is required");
+  if (!projectId) throw new SiaxError("INVALID_REQUEST", "0pt.er", "project_id is required");
+
+  if (!Array.isArray(body.records) || body.records.length < 2 || body.records.length > 5_000) {
+    throw new SiaxError("INVALID_REQUEST", "0pt.er", "records must contain between 2 and 5000 items");
+  }
+  if (
+    !Array.isArray(body.blocking_fields) ||
+    body.blocking_fields.length === 0 ||
+    body.blocking_fields.length > 20 ||
+    !body.blocking_fields.every((v) => typeof v === "string" && v.trim().length > 0)
+  ) {
+    throw new SiaxError("INVALID_REQUEST", "0pt.er", "blocking_fields must contain 1-20 non-empty strings");
+  }
+  if (!Array.isArray(body.compare_fields) || body.compare_fields.length === 0 || body.compare_fields.length > 50) {
+    throw new SiaxError("INVALID_REQUEST", "0pt.er", "compare_fields must contain 1-50 items");
+  }
+
+  const records: ErRecord[] = body.records.map((value, index) => {
+    if (!value || typeof value !== "object" || Array.isArray(value)) {
+      throw new SiaxError("INVALID_REQUEST", "0pt.er", `records[${index}] must be an object`);
+    }
+    const record = value as Record<string, unknown>;
+    if (typeof record.record_id !== "string" || !record.record_id.trim()) {
+      throw new SiaxError("INVALID_REQUEST", "0pt.er", `records[${index}].record_id is required`);
+    }
+    if (!record.fields || typeof record.fields !== "object" || Array.isArray(record.fields)) {
+      throw new SiaxError("INVALID_REQUEST", "0pt.er", `records[${index}].fields must be an object`);
+    }
+    const fields = record.fields as Record<string, unknown>;
+    if (Object.keys(fields).length > 200) {
+      throw new SiaxError("INVALID_REQUEST", "0pt.er", `records[${index}].fields exceeds 200 fields`);
+    }
+    const normalizedFields: ErRecord["fields"] = {};
+    for (const [field, fieldValue] of Object.entries(fields)) {
+      if (!field.trim()) throw new SiaxError("INVALID_REQUEST", "0pt.er", `records[${index}] contains an empty field name`);
+      if (
+        fieldValue !== null &&
+        fieldValue !== undefined &&
+        typeof fieldValue !== "string" &&
+        typeof fieldValue !== "number"
+      ) {
+        throw new SiaxError(
+          "INVALID_REQUEST",
+          "0pt.er",
+          `records[${index}].fields.${field} must be string, number, null or undefined`,
+        );
+      }
+      normalizedFields[field.trim()] = fieldValue as string | number | null | undefined;
+    }
+    return { record_id: record.record_id.trim(), fields: normalizedFields };
+  });
+
+  if (new Set(records.map((record) => record.record_id)).size !== records.length) {
+    throw new SiaxError("INVALID_REQUEST", "0pt.er", "record_id values must be unique within the request");
+  }
+
+  const compareFields = body.compare_fields.map((value, index) => {
+    if (!value || typeof value !== "object" || Array.isArray(value)) {
+      throw new SiaxError("INVALID_REQUEST", "0pt.er", `compare_fields[${index}] must be an object`);
+    }
+    const item = value as Record<string, unknown>;
+    if (typeof item.field !== "string" || !item.field.trim()) {
+      throw new SiaxError("INVALID_REQUEST", "0pt.er", `compare_fields[${index}].field is required`);
+    }
+    const weight = item.weight === undefined ? undefined : Number(item.weight);
+    if (weight !== undefined && (!Number.isFinite(weight) || weight < 0 || weight > 100)) {
+      throw new SiaxError("INVALID_REQUEST", "0pt.er", `compare_fields[${index}].weight must be between 0 and 100`);
+    }
+    return { field: item.field.trim(), ...(weight !== undefined ? { weight } : {}) };
+  });
+
+  const autoThreshold = finiteThreshold(body.auto_match_threshold, "auto_match_threshold", 0.9);
+  const reviewThreshold = finiteThreshold(body.review_threshold, "review_threshold", 0.6);
+  if (reviewThreshold >= autoThreshold) {
+    throw new SiaxError("INVALID_REQUEST", "0pt.er", "review_threshold must be lower than auto_match_threshold");
+  }
+
+  return {
+    tenant_id: tenantId,
+    project_id: projectId,
+    records,
+    blocking_fields: (body.blocking_fields as string[]).map((value) => value.trim()),
+    compare_fields: compareFields,
+    auto_match_threshold: autoThreshold,
+    review_threshold: reviewThreshold,
+    ...(typeof body.correlation_id === "string" && body.correlation_id.trim()
+      ? { correlation_id: body.correlation_id.trim() }
+      : {}),
+  };
+}