danielmiessler/Fabric · error · Error

Fabric API error: ${fabricResponse.statusText}

Error message

Fabric API error: ${fabricResponse.statusText}

What it means

Thrown by the SvelteKit /chat server endpoint when it proxies the request to the local Fabric backend and fabricResponse.ok is false. The Fabric REST service (fabric --serve) returned a 4xx/5xx; common causes are an unknown pattern name, missing/invalid API key for the configured vendor, an unreachable or misconfigured model, or the server rejecting the request payload. The thrown message only carries statusText, which hides the backend's error body.

Source

Thrown at web/src/routes/chat/+server.ts:111

      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify(body)
    });

    console.log('6. Fabric response:', {
      status: fabricResponse.status,
      ok: fabricResponse.ok,
      statusText: fabricResponse.statusText
    });

    if (!fabricResponse.ok) {
      console.error('Error from Fabric API:', {
        status: fabricResponse.status,
        statusText: fabricResponse.statusText
      });
      throw new Error(`Fabric API error: ${fabricResponse.statusText}`);
    }

    const stream = fabricResponse.body;
    if (!stream) {
      throw new Error('No response from fabric backend');
    }

    // Create a TransformStream to inspect the data without modifying it
    const transformStream = new TransformStream({
      transform(chunk, controller) {
        const text = new TextDecoder().decode(chunk);
        if (text.startsWith('data: ')) {
          try {
            const data = JSON.parse(text.slice(6));
            console.log('Stream chunk format:', {
              type: data.type,
              format: data.format,
              contentLength: data.content?.length

View on GitHub (pinned to 338b89cfe9)

Solutions

1. Read the Fabric server's own logs/console output for the matching request — the endpoint already logs status and statusText just above the throw
2. Verify the vendor API keys exist in Fabric's .env and that the selected model is valid for that vendor
3. Confirm the pattern name sent in the request exists (fabric --listpatterns / patterns dir) and matches exactly
4. Check the FABRIC backend URL/port the endpoint targets and that the running fabric --serve version matches what the UI expects
5. Forward the backend error body instead of statusText so the UI shows the real reason

Example fix

// before
if (!fabricResponse.ok) {
  console.error('Error from Fabric API:', { status: fabricResponse.status, statusText: fabricResponse.statusText });
  throw new Error(`Fabric API error: ${fabricResponse.statusText}`);
}

// after
if (!fabricResponse.ok) {
  const errBody = await fabricResponse.text().catch(() => '');
  console.error('Error from Fabric API:', { status: fabricResponse.status, statusText: fabricResponse.statusText, body: errBody });
  throw error(fabricResponse.status, `Fabric API error: ${errBody || fabricResponse.statusText}`);
}

// Sanity-check the request before proxying
if (!pattern) throw error(400, 'Missing pattern');
const fabricBase = env.FABRIC_URL ?? 'http://localhost:8080';
// Optional liveness probe before the real call
const health = await fetch(`${fabricBase}/health`, { signal: AbortSignal.timeout(2000) }).catch(() => null);
if (!health?.ok) throw error(502, 'Fabric backend unreachable');

try {
  const fabricResponse = await fetch(fabricUrl, { ...init });
  if (!fabricResponse.ok) {
    const errBody = await fabricResponse.text().catch(() => '');
    throw error(fabricResponse.status, `Fabric API error: ${errBody || fabricResponse.statusText}`);
  }
  // ... stream
} catch (e) {
  if (e && typeof e === 'object' && 'status' in e) throw e; // sveltekit HttpError passthrough
  throw error(502, `Fabric backend request failed: ${String(e)}`);
}

When it happens

Trigger: POST /chat with a pattern the backend does not have (404), vendor API key missing/expired (401/500 from Fabric), model name not available to the vendor (400), Fabric server on a different port or an older version with different routes (404), or payload fields the server rejects (422).

Common situations: Fabric config (~/.config/fabric/.env) missing OPENAI/ANTHROPIC keys, pattern renamed or removed from the patterns dir, Fabric CLI updated with breaking API changes while the web UI was not, env vars not loaded into the process serving the endpoint.

Related errors

• HTTP error! status: ${response.status}
• await response.text()
• Failed to load session: ${response.statusText}
• No output received from create_pattern
• HTTP_ERROR

AI-assisted analysis of danielmiessler/Fabric@338b89cfe9 (2026-08-15). Data as JSON: /api/errors/3d09d740884a70d2. Report an issue: GitHub.