diff --git a/apps/sim/app/api/v2/lib/response.ts b/apps/sim/app/api/v2/lib/response.ts
index 82459661bec..1e95d321f71 100644
--- a/apps/sim/app/api/v2/lib/response.ts
+++ b/apps/sim/app/api/v2/lib/response.ts
@@ -22,6 +22,7 @@ import {
   type OrchestrationErrorCode,
 } from '@/lib/core/orchestration/types'
 import type { HttpError } from '@/lib/core/utils/http-error'
+import { describeResponseError } from '@/lib/core/utils/response-error'
 import type { RateLimitResult } from '@/app/api/v1/middleware'
 
 /**
@@ -217,7 +218,7 @@ export function v2Error(
   const retryAfterSeconds = options.omitRetryAfter
     ? undefined
     : RETRY_AFTER_SECONDS_BY_STATUS[status]
-  return NextResponse.json(
+  const response = NextResponse.json(
     { error },
     {
       status,
@@ -229,6 +230,15 @@ export function v2Error(
       },
     }
   )
+  const reason = detailCode(options.details)
+  describeResponseError(response, { errorCode: code, ...(reason ? { errorReason: reason } : {}) })
+  return response
+}
+
+/** The cause a refusal names in `details.code`, a closed vocabulary safe to log. */
+function detailCode(details: unknown): string | undefined {
+  if (typeof details !== 'object' || details === null || !('code' in details)) return undefined
+  return typeof details.code === 'string' ? details.code : undefined
 }
 
 /** Renders a trusted typed HTTP error without changing the v2 envelope. */
@@ -267,9 +277,17 @@ export function v2ValidationError(error: ZodError, slice?: RequestSlice): NextRe
       ? issueMessage.slice(fieldLabel.length)
       : issueMessage
   const location = [slice, ...path].filter((part) => part !== undefined && part !== '').join('.')
-  return v2Error('BAD_REQUEST', location ? `${location}: ${message}` : message, {
+  const response = v2Error('BAD_REQUEST', location ? `${location}: ${message}` : message, {
     details: serializeZodIssues(error),
   })
+  // Deeper segments can be record keys the caller wrote (an import's CSV headers); no slice is itself a record.
+  const field = [slice, path[0]].filter((part) => part !== undefined && part !== '').join('.')
+  describeResponseError(response, {
+    errorCode: 'BAD_REQUEST',
+    ...(field ? { errorField: field } : {}),
+    ...(error.issues[0] ? { errorReason: error.issues[0].code } : {}),
+  })
+  return response
 }
 
 /**
diff --git a/apps/sim/lib/core/utils/response-error.ts b/apps/sim/lib/core/utils/response-error.ts
new file mode 100644
index 00000000000..a7445a0e68b
--- /dev/null
+++ b/apps/sim/lib/core/utils/response-error.ts
@@ -0,0 +1,30 @@
+/**
+ * The machine-readable part of an error response, kept beside the response so
+ * the route handler's closing log line can be grouped by why a request was
+ * refused without reading the body. Never the message, which can quote user
+ * input.
+ */
+export interface ResponseErrorSummary {
+  /** The stable error code the body carries, e.g. `BAD_REQUEST`. */
+  errorCode: string
+  /** For a validation failure, the request slice and its declared top-level field, e.g. `body.mapping`. */
+  errorField?: string
+  /** The cause the refusal named (`READ_ONLY_API_KEY`) or the validation issue kind (`invalid_type`). */
+  errorReason?: string
+}
+
+/**
+ * Keyed by the response object, so only a response a route actually returns is
+ * ever read back. One built only to extract its message is never logged.
+ */
+const summaries = new WeakMap<Response, ResponseErrorSummary>()
+
+/** Records what `response` tells its caller; a later call for the same response replaces it. */
+export function describeResponseError(response: Response, summary: ResponseErrorSummary): void {
+  summaries.set(response, summary)
+}
+
+/** What `describeResponseError` recorded for `response`, if anything. */
+export function readResponseError(response: Response): ResponseErrorSummary | undefined {
+  return summaries.get(response)
+}
diff --git a/apps/sim/lib/core/utils/with-route-handler.ts b/apps/sim/lib/core/utils/with-route-handler.ts
index 7a5fc3889c4..7de2af3d220 100644
--- a/apps/sim/lib/core/utils/with-route-handler.ts
+++ b/apps/sim/lib/core/utils/with-route-handler.ts
@@ -15,6 +15,7 @@ import { ADMISSION_RETRY_AFTER_SECONDS } from '@/lib/core/admission/transient-fa
 import { FILE_DELIVERY_CSP_PATH_PATTERN, getMainCSPPolicy } from '@/lib/core/security/csp'
 import { HttpError } from '@/lib/core/utils/http-error'
 import { generateRequestId } from '@/lib/core/utils/request'
+import { readResponseError } from '@/lib/core/utils/response-error'
 import { MAX_CALL_CHAIN_DEPTH, parseCallChain, SIM_VIA_HEADER } from '@/lib/execution/call-chain'
 import { trackInFlightRequest } from '@/lib/monitoring/in-flight-requests'
 import { withPermissionGroupScope } from '@/lib/permission-groups/request-scope.server'
@@ -274,9 +275,9 @@ export function withRouteHandler<T>(
       const duration = Date.now() - startTime
 
       if (status >= 500) {
-        logger.error('Server error response', { status, duration })
+        logger.error('Server error response', { status, duration, ...readResponseError(response) })
       } else if (status >= 400) {
-        logger.warn('Client error response', { status, duration })
+        logger.warn('Client error response', { status, duration, ...readResponseError(response) })
       } else if (status > 0) {
         logger.info('OK', { status, duration })
       }