diff --git a/src/lib/error-interceptor.ts b/src/lib/error-interceptor.ts
index ec297709..b0f05a06 100644
--- a/src/lib/error-interceptor.ts
+++ b/src/lib/error-interceptor.ts
@@ -18,14 +18,18 @@ export const errorInterceptor = async (err: unknown): Promise<void> => {
   if (status == null) throw err
 
   if (status === 401) {
-    throw new SeamHttpUnauthorizedError(requestId)
+    throw new SeamHttpUnauthorizedError(
+      requestId,
+      isApiErrorResponse(response) ? response.data.error : undefined,
+      { cause: err },
+    )
   }
 
   if (!isApiErrorResponse(response)) throw err
 
   const { type } = response.data.error
 
-  const args = [response.data.error, status, requestId] as const
+  const args = [response.data.error, status, requestId, { cause: err }] as const
 
   if (type === 'invalid_input') throw new SeamHttpInvalidInputError(...args)
   throw new SeamHttpApiError(...args)
diff --git a/src/lib/seam-http-error.ts b/src/lib/seam-http-error.ts
index e6450e3a..a0a73a85 100644
--- a/src/lib/seam-http-error.ts
+++ b/src/lib/seam-http-error.ts
@@ -22,9 +22,14 @@ export class SeamHttpApiError extends Error {
    */
   data?: unknown
 
-  constructor(error: ApiError, statusCode: number, requestId: string) {
+  constructor(
+    error: ApiError,
+    statusCode: number,
+    requestId: string,
+    options: ErrorOptions = {},
+  ) {
     const { type, message, data } = error
-    super(message)
+    super(message, options)
     this.name = this.constructor.name
     this.code = type
     this.statusCode = statusCode
@@ -49,10 +54,15 @@ export class SeamHttpUnauthorizedError extends SeamHttpApiError {
   override code: 'unauthorized'
   override statusCode: 401
 
-  constructor(requestId: string) {
+  constructor(requestId: string, error?: ApiError, options: ErrorOptions = {}) {
     const type = 'unauthorized'
     const status = 401
-    super({ type, message: 'Unauthorized' }, status, requestId)
+    super(
+      error ?? { type, message: 'Unauthorized' },
+      status,
+      requestId,
+      options,
+    )
     this.name = this.constructor.name
     this.code = type
     this.statusCode = status
@@ -77,13 +87,34 @@ export class SeamHttpInvalidInputError extends SeamHttpApiError {
 
   readonly #validationErrors: NonNullable<ApiError['validation_errors']>
 
-  constructor(error: ApiError, statusCode: number, requestId: string) {
-    super(error, statusCode, requestId)
+  constructor(
+    error: ApiError,
+    statusCode: number,
+    requestId: string,
+    options: ErrorOptions = {},
+  ) {
+    super(error, statusCode, requestId, options)
     this.name = this.constructor.name
     this.code = 'invalid_input'
     this.#validationErrors = error.validation_errors ?? {}
   }
 
+  /**
+   * Validation errors returned by the Seam API, keyed by parameter name.
+   */
+  get validationErrors(): NonNullable<ApiError['validation_errors']> {
+    return this.#validationErrors
+  }
+
+  /**
+   * Names of the request parameters that failed validation.
+   */
+  get validationErrorParamNames(): string[] {
+    return Object.keys(this.#validationErrors).filter(
+      (name) => name !== '_errors',
+    )
+  }
+
   /**
    * Returns the validation error messages for the request parameter,
    * or an empty array if the parameter had no validation errors.
diff --git a/test/seam/connect/http-error.test.ts b/test/seam/connect/http-error.test.ts
index be435869..ed0cf7b3 100644
--- a/test/seam/connect/http-error.test.ts
+++ b/test/seam/connect/http-error.test.ts
@@ -1,6 +1,7 @@
 import test from 'ava'
-import { AxiosError, AxiosHeaders } from 'axios'
+import { AxiosError, AxiosHeaders, isAxiosError } from 'axios'
 import { getTestServer } from 'fixtures/seam/connect/api.js'
+import nock from 'nock'
 
 import {
   errorInterceptor,
@@ -126,4 +127,98 @@ test('SeamHttp: throws SeamHttpInvalidInputError on invalid input', async (t) =>
   t.deepEqual(err?.getValidationErrorMessages('device_ids'), [
     'Expected array, received number',
   ])
+  t.deepEqual(err?.validationErrorParamNames, ['device_ids'])
+  t.deepEqual(err?.validationErrors['device_ids']?._errors, [
+    'Expected array, received number',
+  ])
+})
+
+test('SeamHttp: errors retain the AxiosError as cause', async (t) => {
+  const { seed, endpoint } = await getTestServer(t)
+
+  const seam = SeamHttp.fromApiKey(seed.seam_apikey1_token, {
+    endpoint,
+    axiosRetryOptions: {
+      retries: 0,
+    },
+  })
+
+  const err = await t.throwsAsync(
+    async () => await seam.devices.get({ device_id: 'unknown-device' }),
+    {
+      instanceOf: SeamHttpApiError,
+    },
+  )
+
+  if (!isAxiosError(err?.cause)) {
+    t.fail('Expected cause to be the AxiosError')
+    return
+  }
+
+  t.is(err.cause.response?.status, 404)
+  t.truthy(err.cause.config)
+})
+
+test('SeamHttp: unauthorized error surfaces the API error message', async (t) => {
+  const { seed, endpoint } = await getTestServer(t)
+
+  const seam = SeamHttp.fromApiKey(seed.seam_apikey1_token, {
+    endpoint,
+    axiosRetryOptions: {
+      retries: 0,
+    },
+  })
+
+  nock(endpoint)
+    .get('/devices/get')
+    .query(true)
+    .reply(
+      401,
+      {
+        error: {
+          type: 'unauthorized',
+          message: 'Custom unauthorized message from the server',
+        },
+      },
+      { 'Content-Type': 'application/json', 'seam-request-id': 'request-1' },
+    )
+
+  const err = await t.throwsAsync(
+    async () => await seam.devices.get({ device_id: 'unknown-device' }),
+    {
+      instanceOf: SeamHttpUnauthorizedError,
+      message: 'Custom unauthorized message from the server',
+    },
+  )
+
+  t.is(err?.code, 'unauthorized')
+  t.is(err?.statusCode, 401)
+  t.is(err?.requestId, 'request-1')
+  t.true(isAxiosError(err?.cause))
+})
+
+test('SeamHttp: unauthorized error falls back without an API error body', async (t) => {
+  const { seed, endpoint } = await getTestServer(t)
+
+  const seam = SeamHttp.fromApiKey(seed.seam_apikey1_token, {
+    endpoint,
+    axiosRetryOptions: {
+      retries: 0,
+    },
+  })
+
+  nock(endpoint)
+    .get('/devices/get')
+    .query(true)
+    .reply(401, 'Unauthorized', { 'Content-Type': 'text/plain' })
+
+  const err = await t.throwsAsync(
+    async () => await seam.devices.get({ device_id: 'unknown-device' }),
+    {
+      instanceOf: SeamHttpUnauthorizedError,
+      message: 'Unauthorized',
+    },
+  )
+
+  t.is(err?.code, 'unauthorized')
 })