Claude Code Connection Errors: A Relay Fix Guide
Why Claude Code usually fails
When Claude Code throws a connection or auth error, the root cause is usually one of four things: a bad API key, the wrong base URL, a model name the relay does not recognize, or a network layer that blocks outbound HTTPS. The fastest way to debug is to test the API outside Claude Code first.
Use a known-good 59API setup
59API is a low-cost AI API relay for Claude and GPT models that stays compatible with Claude Code and other Anthropic-style clients. If you want official-quality model output without paying premium rates, point Claude Code at https://api.59api.com and use your 59API key.
In a Unix shell, start with: export ANTHROPIC_API_KEY='your_59api_key'; export ANTHROPIC_BASE_URL='https://api.59api.com'; claude
If you are on Windows, set the same values in your terminal session or system environment variables, then restart Claude Code so it reads the new settings.
- Check the key value first. Copy-paste mistakes are common, especially leading or trailing spaces.
- Check the base URL exactly. Use https://api.59api.com, not a browser URL, a dashboard URL, or an old staging endpoint.
- Use a supported model. If your request hard-codes a model string, make sure it matches a Claude model available in your account.
Test the relay before reopening Claude Code
Run one direct request. If this works, Claude Code is misconfigured; if it fails, the problem is in the key, model, or network.
curl https://api.59api.com/v1/messages -H 'x-api-key: your_59api_key' -H 'anthropic-version: 2023-06-01' -H 'content-type: application/json' -d '{"model":"claude-3-5-sonnet-20241022","max_tokens":32,"messages":[{"role":"user","content":"Say OK"}]}'
If you get a normal JSON response, your relay path is healthy. That means the next step is to compare Claude Code’s environment variables with the working curl command.
Read the error code like a checklist
- 401 Unauthorized: the key is missing, expired, copied incorrectly, or stored in the wrong variable.
- 403 Forbidden: your account may not have enough balance, or the requested model is not available for that key.
- 404 Not Found: the base URL or path is wrong. Confirm the request is going to /v1/messages on https://api.59api.com.
- 429 Too Many Requests: slow down retries, reduce concurrency, and add backoff. A cheap relay still has real throughput limits.
- ECONNRESET, ETIMEDOUT, TLS errors: test again with curl, disable VPN or proxy temporarily, and check corporate firewall rules.
A minimal Node.js sanity check
Use the same endpoint in a tiny script so you know the relay works independently of Claude Code. This is also useful if you use the OpenAI SDK elsewhere and want to isolate the problem.
const res = await fetch('https://api.59api.com/v1/messages', { method: 'POST', headers: { 'x-api-key': process.env.ANTHROPIC_API_KEY, 'anthropic-version': '2023-06-01', 'content-type': 'application/json' }, body: JSON.stringify({ model: 'claude-3-5-sonnet-20241022', max_tokens: 32, messages: [{ role: 'user', content: 'Hello' }] }) }); console.log(await res.text());
If that returns content, your auth and network are fine. The remaining issue is usually a Claude Code config mismatch, not a relay problem.
Why 59API is a practical debugging choice
Because 59API is pay-as-you-go and among the cheapest relays, you can run repeated tests without burning budget. That matters when you are iterating on auth headers, base URLs, or model names. You still get native, official-quality Claude models with no downgrade, so you are debugging the integration rather than second-guessing model quality. The referral rebate is also helpful if you plan to keep testing or move a team onto the same workflow.
If you want a lower-cost place to verify Claude Code today, sign up for 59API, grab a key, and rerun the curl test before changing anything else. In most cases, the fix is just one env var away.