diff --git a/src/providers/firecrawl.test.ts b/src/providers/firecrawl.test.ts
index b74ad50..4470a94 100644
--- a/src/providers/firecrawl.test.ts
+++ b/src/providers/firecrawl.test.ts
@@ -168,3 +168,46 @@ test("createFirecrawlProvider fetches each URL via /scrape and preserves per-url
     },
   ]);
 });
+
+test("createFirecrawlProvider limits concurrent scrape requests", async () => {
+  let active = 0;
+  let maxActive = 0;
+
+  const provider = createFirecrawlProvider(cloudConfig, async (_url, init) => {
+    active += 1;
+    maxActive = Math.max(maxActive, active);
+
+    const body = JSON.parse(String(init?.body));
+    await new Promise((resolve) => setTimeout(resolve, 10));
+
+    active -= 1;
+    return new Response(
+      JSON.stringify({
+        success: true,
+        data: {
+          metadata: {
+            title: body.url,
+            sourceURL: body.url,
+          },
+          markdown: `Fetched ${body.url}`,
+        },
+      }),
+      { status: 200 },
+    );
+  });
+
+  const urls = [
+    "https://a.example",
+    "https://b.example",
+    "https://c.example",
+    "https://d.example",
+    "https://e.example",
+    "https://f.example",
+    "https://g.example",
+  ];
+
+  const result = await provider.fetch({ urls });
+
+  assert.equal(result.results.length, urls.length);
+  assert.ok(maxActive <= 4, `expected max concurrency <= 4, got ${maxActive}`);
+});
diff --git a/src/providers/firecrawl.ts b/src/providers/firecrawl.ts
index 216ef92..52d6d59 100644
--- a/src/providers/firecrawl.ts
+++ b/src/providers/firecrawl.ts
@@ -9,6 +9,7 @@ import type {
 } from "./types.ts";
 
 const DEFAULT_FIRECRAWL_BASE_URL = "https://api.firecrawl.dev/v2";
+const DEFAULT_FIRECRAWL_FETCH_CONCURRENCY = 4;
 
 type FirecrawlSearchPayload = {
   id?: string;
@@ -124,6 +125,26 @@ function resolveFetchFormats(request: NormalizedFetchRequest) {
   return uniqueFormats(formats.length > 0 ? formats : ["markdown"]);
 }
 
+async function mapWithConcurrency<TItem, TResult>(
+  items: TItem[],
+  concurrency: number,
+  iteratee: (item: TItem) => Promise<TResult>,
+): Promise<TResult[]> {
+  const results = new Array<TResult>(items.length);
+  let nextIndex = 0;
+
+  const workers = Array.from({ length: Math.max(1, Math.min(concurrency, items.length)) }, async () => {
+    while (nextIndex < items.length) {
+      const currentIndex = nextIndex;
+      nextIndex += 1;
+      results[currentIndex] = await iteratee(items[currentIndex]!);
+    }
+  });
+
+  await Promise.all(workers);
+  return results;
+}
+
 function pickRequestId(payload: { id?: string; request_id?: string }) {
   return typeof payload.id === "string"
     ? payload.id
@@ -180,37 +201,35 @@ export function createFirecrawlProvider(
       validateFirecrawlFetchRequest(config.name, request);
       const formats = resolveFetchFormats(request);
 
-      const results = await Promise.all(
-        request.urls.map(async (url) => {
-          try {
-            const payload = await postJson<FirecrawlScrapePayload>({
-              providerName: config.name,
-              baseUrl,
-              path: "/scrape",
-              apiKey: config.apiKey,
-              fetchImpl,
-              body: {
-                url,
-                formats,
-              },
-            });
-
-            return {
-              url: payload.data?.metadata?.sourceURL ?? url,
-              title: payload.data?.metadata?.title ?? payload.data?.title ?? null,
-              text: typeof payload.data?.markdown === "string" ? payload.data.markdown : undefined,
-              summary: typeof payload.data?.summary === "string" ? payload.data.summary : undefined,
-              images: Array.isArray(payload.data?.images) ? payload.data.images : undefined,
-            };
-          } catch (error) {
-            return {
+      const results = await mapWithConcurrency(request.urls, DEFAULT_FIRECRAWL_FETCH_CONCURRENCY, async (url) => {
+        try {
+          const payload = await postJson<FirecrawlScrapePayload>({
+            providerName: config.name,
+            baseUrl,
+            path: "/scrape",
+            apiKey: config.apiKey,
+            fetchImpl,
+            body: {
               url,
-              title: null,
-              error: (error as Error).message,
-            };
-          }
-        }),
-      );
+              formats,
+            },
+          });
+
+          return {
+            url: payload.data?.metadata?.sourceURL ?? url,
+            title: payload.data?.metadata?.title ?? payload.data?.title ?? null,
+            text: typeof payload.data?.markdown === "string" ? payload.data.markdown : undefined,
+            summary: typeof payload.data?.summary === "string" ? payload.data.summary : undefined,
+            images: Array.isArray(payload.data?.images) ? payload.data.images : undefined,
+          };
+        } catch (error) {
+          return {
+            url,
+            title: null,
+            error: error instanceof Error ? error.message : String(error),
+          };
+        }
+      });
 
       return {
         providerName: config.name,
diff --git a/src/providers/http.test.ts b/src/providers/http.test.ts
new file mode 100644
index 0000000..caa20a5
--- /dev/null
+++ b/src/providers/http.test.ts
@@ -0,0 +1,24 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { postJson } from "./http.ts";
+
+test("postJson surfaces invalid JSON responses with HTTP context", async () => {
+  await assert.rejects(
+    () =>
+      postJson({
+        providerName: "firecrawl-main",
+        baseUrl: "https://api.firecrawl.dev/v2",
+        path: "/search",
+        body: { query: "pi docs" },
+        fetchImpl: async () =>
+          new Response("<html>not json</html>", {
+            status: 200,
+            statusText: "OK",
+            headers: {
+              "content-type": "text/html",
+            },
+          }),
+      }),
+    /Provider "firecrawl-main" HTTP 200 OK: invalid JSON response: <html>not json<\/html>/,
+  );
+});
diff --git a/src/providers/http.ts b/src/providers/http.ts
index 93f6cea..02177f5 100644
--- a/src/providers/http.ts
+++ b/src/providers/http.ts
@@ -15,11 +15,13 @@ export function joinApiUrl(baseUrl: string, path: string) {
   return `${normalizedBaseUrl}${normalizedPath}`;
 }
 
+function formatHttpErrorMessage(providerName: string, response: Response, text: string) {
+  return `Provider "${providerName}" HTTP ${response.status} ${response.statusText}: ${text.slice(0, 300)}`;
+}
+
 export async function readHttpError(providerName: string, response: Response): Promise<never> {
   const text = await response.text();
-  throw new Error(
-    `Provider "${providerName}" HTTP ${response.status} ${response.statusText}: ${text.slice(0, 300)}`,
-  );
+  throw new Error(formatHttpErrorMessage(providerName, response, text));
 }
 
 export async function postJson<T>({
@@ -44,9 +46,14 @@ export async function postJson<T>({
     body: JSON.stringify(body),
   });
 
+  const text = await response.text();
   if (!response.ok) {
-    await readHttpError(providerName, response);
+    throw new Error(formatHttpErrorMessage(providerName, response, text));
   }
 
-  return (await response.json()) as T;
+  try {
+    return JSON.parse(text) as T;
+  } catch {
+    throw new Error(formatHttpErrorMessage(providerName, response, `invalid JSON response: ${text}`));
+  }
 }
diff --git a/src/providers/registry.ts b/src/providers/registry.ts
index 5a34c5c..d2fbd5d 100644
--- a/src/providers/registry.ts
+++ b/src/providers/registry.ts
@@ -107,8 +107,16 @@ export function getProviderDescriptor(provider: Pick<WebSearchProviderConfig, "t
 }
 
 export function createProviderFromConfig(providerConfig: WebSearchProviderConfig) {
-  const descriptor = getProviderDescriptor(providerConfig);
-  return descriptor.createProvider(providerConfig as never);
+  switch (providerConfig.type) {
+    case "exa":
+      return providerDescriptors.exa.createProvider(providerConfig);
+    case "tavily":
+      return providerDescriptors.tavily.createProvider(providerConfig);
+    case "firecrawl":
+      return providerDescriptors.firecrawl.createProvider(providerConfig);
+    default:
+      throw new Error(`Unknown provider type: ${(providerConfig as { type: string }).type}`);
+  }
 }
 
 export function validateSearchRequestForProvider(providerName: string, providerConfig: WebSearchProviderConfig, request: NormalizedSearchRequest) {
diff --git a/src/runtime.test.ts b/src/runtime.test.ts
index 91be336..b3fcc32 100644
--- a/src/runtime.test.ts
+++ b/src/runtime.test.ts
@@ -431,7 +431,7 @@ test("search records provider factory failures and follows fallbacks", async ()
     }),
     createProvider(providerConfig) {
       if (providerConfig.name === "firecrawl-main") {
-        throw new Error("factory boom:firecrawl-main");
+        throw "factory boom:firecrawl-main";
       }
 
       return createProvider(providerConfig.name, providerConfig.type, {
diff --git a/src/runtime.ts b/src/runtime.ts
index 85ea565..e44522e 100644
--- a/src/runtime.ts
+++ b/src/runtime.ts
@@ -58,11 +58,14 @@ function buildExecutionMeta(
   };
 }
 
+function describeError(error: unknown) {
+  return error instanceof Error ? error.message : String(error);
+}
+
 function attachAttempts(error: unknown, attempts: ProviderExecutionAttempt[]) {
-  if (error instanceof Error) {
-    (error as Error & { execution?: { attempts: ProviderExecutionAttempt[] } }).execution = { attempts };
-  }
-  return error;
+  const normalizedError = error instanceof Error ? error : new Error(String(error));
+  (normalizedError as Error & { execution?: { attempts: ProviderExecutionAttempt[] } }).execution = { attempts };
+  return normalizedError;
 }
 
 export function createWebSearchRuntime(
@@ -125,7 +128,7 @@ export function createWebSearchRuntime(
         attempts.push({
           providerName,
           status: "failed",
-          reason: (error as Error).message,
+          reason: describeError(error),
         });
         lastError = error;
 
@@ -155,7 +158,7 @@ export function createWebSearchRuntime(
         attempts.push({
           providerName,
           status: "failed",
-          reason: (error as Error).message,
+          reason: describeError(error),
         });
         lastError = error;