diff --git a/README.md b/README.md
index fb06df4..0ac0bcd 100644
--- a/README.md
+++ b/README.md
@@ -299,6 +299,14 @@ it, lives in your local signer instead - see `VECTOR_SIGNER_SPEND_LIMIT_PER_TX`
 > echoes a token value. Commas delimit entries and cannot be escaped, so generate
 > tokens from a comma-free charset (hex / base64url / alphanumeric).
 
+> **Error responses do not echo configured endpoints.** A failed Ogmios, Koios, or
+> submit-API request is reported to the caller by service name and status only -
+> for example "Ogmios request failed (queryLedgerState/utxo): 503 Service
+> Unavailable" - never the configured `VECTOR_OGMIOS_URL` / `VECTOR_KOIOS_URL` /
+> `VECTOR_SUBMIT_URL` value or the raw response body. Full detail goes to the
+> server's own `console.error` log for operators; a caller only ever sees the
+> service name and status.
+
 ### Mainnet endpoints
 
 | Variable | Mainnet value |
diff --git a/packages/builder/src/vector/agent-network.ts b/packages/builder/src/vector/agent-network.ts
index a4eda7f..e242fc9 100644
--- a/packages/builder/src/vector/agent-network.ts
+++ b/packages/builder/src/vector/agent-network.ts
@@ -81,7 +81,7 @@ ${capList}
 **Troubleshooting Tips:**
 1. Verify the DID format: did:vector:agent:{policyId}:{nftAssetName}
 2. The agent may not be registered or may have deregistered
-3. Check that Koios is reachable at ${VECTOR_KOIOS_URL}`,
+3. Verify the configured Koios endpoint is reachable`,
           }],
         };
       }
@@ -133,7 +133,7 @@ ${capList}
             text: `Failed to discover agents: ${err instanceof Error ? err.message : String(err)}
 
 **Troubleshooting Tips:**
-1. Check that Ogmios is reachable at ${VECTOR_OGMIOS_URL}
+1. Verify the configured Ogmios endpoint is reachable
 2. The registry may be empty - no agents have registered yet
 3. Try without filters to list all agents`,
           }],
@@ -189,7 +189,7 @@ The DID above is bound to the exact wallet UTxO this build consumed - if that UT
 **Troubleshooting Tips:**
 1. Ensure the changeAddress wallet holds at least 12 AP3X (10 deposit + fees)
 2. Each wallet can register multiple agents (different one-shot UTxOs)
-3. Verify Ogmios endpoint is reachable at ${VECTOR_OGMIOS_URL}`,
+3. Verify the configured Ogmios endpoint is reachable`,
           }],
         };
       }
diff --git a/packages/builder/src/vector/self-improvement.ts b/packages/builder/src/vector/self-improvement.ts
index b7f270e..2ca49fa 100644
--- a/packages/builder/src/vector/self-improvement.ts
+++ b/packages/builder/src/vector/self-improvement.ts
@@ -197,7 +197,7 @@ Each batch UTxO holds ~30 AP3X for adoption rewards.`,
 
 **Troubleshooting Tips:**
 1. Verify the module contracts are deployed on this network
-2. Check that Ogmios is reachable at ${VECTOR_OGMIOS_URL}
+2. Verify the configured Ogmios endpoint is reachable
 3. The script addresses may not have any UTxOs yet`,
           }],
         };
diff --git a/packages/builder/src/vector/vector.ts b/packages/builder/src/vector/vector.ts
index 028d4c3..087e0a9 100644
--- a/packages/builder/src/vector/vector.ts
+++ b/packages/builder/src/vector/vector.ts
@@ -590,7 +590,7 @@ ${txList}
             text: `Failed to get transaction history: ${error.message}
 
 **Troubleshooting Tips:**
-1. Ensure Koios is configured and reachable: ${VECTOR_KOIOS_URL}
+1. Ensure the configured Koios endpoint is reachable
 2. Verify the address is valid
 3. Check the block explorer for this address`,
           }],
diff --git a/packages/shared/src/provider.ts b/packages/shared/src/provider.ts
index 8f48852..e5c716c 100644
--- a/packages/shared/src/provider.ts
+++ b/packages/shared/src/provider.ts
@@ -78,6 +78,32 @@ export function koiosIndicatesConfirmed(data: unknown): boolean {
   return typeof entry?.num_confirmations === 'number' && entry.num_confirmations > 0;
 }
 
+/**
+ * Format a downstream HTTP or JSON-RPC failure into a message safe to return
+ * to an untrusted caller: names the service, the operation, and the status -
+ * never the endpoint URL, and never the raw response body.
+ *
+ * On a hosted, multi-tenant deployment the configured Ogmios/Koios/submit-api
+ * endpoint is operator infrastructure, not caller information - and a raw
+ * response body from a misconfigured or unreachable endpoint (a reverse-proxy
+ * error page, for instance) can itself echo back hostnames or other detail
+ * that has no business reaching a caller. Call sites console.error the full
+ * detail (status, body, and which endpoint) themselves before throwing this -
+ * full detail to the operator's log, a clean summary to the caller. That
+ * split is the sanitisation.
+ *
+ * Exported and pure so it can be tested without a network round trip - same
+ * rationale as parseSubmitResponse above.
+ */
+export function formatServiceError(
+  service: string,
+  operation: string,
+  status: number | string,
+  statusText?: string,
+): string {
+  return `${service} request failed (${operation}): ${status}${statusText ? ` ${statusText}` : ''}`;
+}
+
 export class OgmiosProvider implements Provider {
   private ogmiosUrl: string;
   private submitUrl: string;
@@ -107,12 +133,14 @@ export class OgmiosProvider implements Provider {
 
     if (!response.ok) {
       const text = await response.text();
-      throw new Error(`Ogmios RPC error (${response.status}): ${text}`);
+      console.error(`[OgmiosProvider] Ogmios RPC error (${method}) at ${this.ogmiosUrl}: ${response.status} ${response.statusText} - ${text}`);
+      throw new Error(formatServiceError('Ogmios', method, response.status, response.statusText));
     }
 
     const json = await response.json();
     if (json.error) {
-      throw new Error(`Ogmios RPC error: ${JSON.stringify(json.error)}`);
+      console.error(`[OgmiosProvider] Ogmios RPC error (${method}) at ${this.ogmiosUrl}:`, json.error);
+      throw new Error(formatServiceError('Ogmios', method, json.error?.code ?? 'error', json.error?.message ?? 'RPC error'));
     }
 
     return json.result;
@@ -333,7 +361,8 @@ export class OgmiosProvider implements Provider {
     });
     if (!response.ok) {
       const text = await response.text();
-      throw new Error(`Koios tx_status query failed (${response.status}): ${text}`);
+      console.error(`[OgmiosProvider] Koios tx_status query failed at ${this.koiosUrl}: ${response.status} ${response.statusText} - ${text}`);
+      throw new Error(formatServiceError('Koios', 'tx_status', response.status, response.statusText));
     }
     return response.json();
   }
@@ -445,7 +474,8 @@ export class OgmiosProvider implements Provider {
 
     if (!txListResponse.ok) {
       const text = await txListResponse.text();
-      throw new Error(`Koios address_txs query failed (${txListResponse.status}): ${text}`);
+      console.error(`[OgmiosProvider] Koios address_txs query failed at ${this.koiosUrl}: ${txListResponse.status} ${txListResponse.statusText} - ${text}`);
+      throw new Error(formatServiceError('Koios', 'address_txs', txListResponse.status, txListResponse.statusText));
     }
 
     const txList: any[] = await txListResponse.json();
@@ -512,7 +542,8 @@ export class OgmiosProvider implements Provider {
 
     if (!response.ok) {
       const errorText = await response.text();
-      throw new Error(`Transaction submission failed (${response.status}): ${errorText}`);
+      console.error(`[OgmiosProvider] Transaction submission failed at ${this.submitUrl}: ${response.status} ${response.statusText} - ${errorText}`);
+      throw new Error(formatServiceError('Submit API', 'submitTx', response.status, response.statusText));
     }
 
     const result = await response.text();
diff --git a/packages/shared/test/provider-error-format.test.ts b/packages/shared/test/provider-error-format.test.ts
new file mode 100644
index 0000000..e7a4e93
--- /dev/null
+++ b/packages/shared/test/provider-error-format.test.ts
@@ -0,0 +1,69 @@
+import { describe, test } from 'node:test';
+import assert from 'node:assert/strict';
+import { formatServiceError } from '../src/provider.ts';
+import { VECTOR_OGMIOS_URL, VECTOR_KOIOS_URL, VECTOR_SUBMIT_URL } from '../src/config.ts';
+
+// The concern (audit E): a hosted deployment's internal Ogmios/Koios/submit-api
+// endpoint reaching an untrusted caller through error text - either the
+// configured URL itself, or a raw response body from a misconfigured/internal
+// endpoint (a reverse-proxy error page, for instance) that can echo back
+// hostnames or other operator-only detail. formatServiceError is the pure
+// function every throw site in provider.ts now routes its caller-visible
+// message through; the full detail (status, body, and which endpoint) goes to
+// console.error instead, at each call site.
+
+describe('formatServiceError', () => {
+  test('names the service, operation, and HTTP status', () => {
+    assert.equal(
+      formatServiceError('Ogmios', 'queryLedgerState/utxo', 503, 'Service Unavailable'),
+      'Ogmios request failed (queryLedgerState/utxo): 503 Service Unavailable',
+    );
+  });
+
+  test('covers Koios and the submit API with the same shape', () => {
+    assert.equal(
+      formatServiceError('Koios', 'tx_status', 502, 'Bad Gateway'),
+      'Koios request failed (tx_status): 502 Bad Gateway',
+    );
+    assert.equal(
+      formatServiceError('Submit API', 'submitTx', 400, 'Bad Request'),
+      'Submit API request failed (submitTx): 400 Bad Request',
+    );
+  });
+
+  test('omits the status text when the caller has none (a JSON-RPC error code, not an HTTP status)', () => {
+    assert.equal(
+      formatServiceError('Ogmios', 'queryLedgerState/utxo', -32602),
+      'Ogmios request failed (queryLedgerState/utxo): -32602',
+    );
+  });
+
+  test('never contains any configured endpoint URL', () => {
+    // Structural, not incidental: the function has no parameter for a URL or
+    // a response body, so it cannot forward either - but pin it against the
+    // actual values in config.ts (the ones a hosted deployment sets to its
+    // own internal endpoints) so a future signature change that threads one
+    // through fails this test by name.
+    const messages = [
+      formatServiceError('Ogmios', 'queryLedgerState/utxo', 503, 'Service Unavailable'),
+      formatServiceError('Koios', 'address_txs', 500, 'Internal Server Error'),
+      formatServiceError('Submit API', 'submitTx', 400, 'Bad Request'),
+    ];
+    for (const url of [VECTOR_OGMIOS_URL, VECTOR_KOIOS_URL, VECTOR_SUBMIT_URL]) {
+      for (const msg of messages) {
+        assert.ok(!msg.includes(url), `message leaked a configured endpoint URL: ${msg}`);
+      }
+    }
+  });
+
+  test('never contains a raw response body, only what the caller passes as status/statusText', () => {
+    // Simulates the shape of a real leak: an upstream failure whose body
+    // echoes infrastructure detail no caller should see. formatServiceError
+    // is never given the body, so it cannot reproduce it - this pins that a
+    // future edit cannot casually splice ${text} back into the template.
+    const leakyBody = 'upstream connect error: could not connect to ogmios-internal.vector.svc.cluster.local:1337';
+    const msg = formatServiceError('Ogmios', 'queryLedgerState/utxo', 502, 'Bad Gateway');
+    assert.ok(!msg.includes(leakyBody));
+    assert.ok(!msg.includes('cluster.local'));
+  });
+});