jackwener/OpenCLI · error · CommandExecutionError

coingecko categories returned malformed JSON: ${err?.message

Error message

coingecko categories returned malformed JSON: ${err?.message ?? err}

What it means

The HTTP response body could not be parsed as JSON; the CLI catches resp.json() failure and wraps it in a CommandExecutionError with the parse error. Typically the API returned HTML (error page, challenge page) instead of JSON.

Source

Thrown at clis/coingecko/categories.js:60

        }
        catch (err) {
            throw new CommandExecutionError(`coingecko categories request failed: ${err?.message ?? err}`);
        }
        if (resp.status === 429) {
            throw new CommandExecutionError(
                'coingecko returned HTTP 429 (rate limited)',
                'Free tier allows ~30 calls/min. Wait and retry.',
            );
        }
        if (!resp.ok) {
            throw new CommandExecutionError(`coingecko categories returned HTTP ${resp.status}`);
        }
        let data;
        try {
            data = await resp.json();
        }
        catch (err) {
            throw new CommandExecutionError(`coingecko categories returned malformed JSON: ${err?.message ?? err}`);
        }
        if (!Array.isArray(data) || !data.length) {
            throw new EmptyResultError('coingecko categories', 'CoinGecko returned no category data.');
        }
        return data.slice(0, limit).map((cat, i) => ({
            rank: i + 1,
            id: String(cat.id ?? ''),
            name: String(cat.name ?? ''),
            marketCap: cat.market_cap != null ? Number(cat.market_cap) : null,
            volume24h: cat.volume_24h != null ? Number(cat.volume_24h) : null,
            marketCapChange24hPct: cat.market_cap_change_24h != null ? Number(cat.market_cap_change_24h) : null,
            top3Coins: Array.isArray(cat.top_3_coins_id) ? cat.top_3_coins_id.join(', ') : '',
        }));
    },
});

View on GitHub (pinned to 49907e53dc)

Solutions

Retry after a delay — often transient
Check whether a proxy/CDN is intercepting the response and bypass it
Inspect the raw response (curl the URL) to see what body is actually returned

Defensive patterns

Strategy: try-catch

Validate before calling

// verify the endpoint returns JSON before relying on it
const probe = await fetch('https://api.coingecko.com/api/v3/coins/categories?limit=1');
const ct = probe.headers.get('content-type') || '';
if (!ct.includes('application/json')) throw new Error('CoinGecko not returning JSON');

Type guard

function isJsonArray(v) {
  return Array.isArray(v);
}

Try / catch

try {
  await runCategories(args);
} catch (err) {
  if (err instanceof CommandExecutionError && /malformed JSON/.test(err.message)) {
    await sleep(5000);
    return runCategories(args); // often a transient HTML error page
  }
  throw err;
}

Prevention

Check content-type before parsing JSON in custom clients
Bypass intercepting proxies/VPN that inject HTML pages
Space out requests to avoid Cloudflare-style challenges

When it happens

Trigger: resp.json() throws because the body is HTML/text — e.g. a Cloudflare challenge, gateway error page, or truncated response from api.coingecko.com.

Common situations: CoinGecko outage returning an HTML error page; ISP/proxy interception page; CDN challenge (Cloudflare) triggered by rate or bot detection.

Understand the failure class

Background: "Invalid JSON response" and "Failed to parse response" errors: when an API answers 200 but the body isn't the JSON your library expected — this error's family across 28 libraries.

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of jackwener/OpenCLI@49907e53dc (2026-08-29). Data as JSON: /api/errors/020e573504c48475. Report an issue: GitHub.