jeremylongshore Anthropic Common Errors
Overview
Quick reference for all Claude API error types with exact HTTP codes, error bodies, and fixes. The API returns errors as JSON: {"type": "error", "error": {"type": "...", "message": "..."}}.
Error Reference
400 — invalid_request_error
{"type": "error", "error": {"type": "invalid_request_error", "message": "messages: roles must alternate between \"user\" and \"assistant\""}}
Common causes and fixes:
| Message Pattern | Cause | Fix |
|---|---|---|
messages: roles must alternate |
Consecutive same-role messages | Merge adjacent user/assistant messages |
max_tokens: must be >= 1 |
Missing or zero max_tokens |
Always set max_tokens (required param) |
model: invalid model id |
Typo in model name | Use exact ID: claude-sonnet-4-20250514 |
messages.0.content: empty |
Empty message content | Ensure content is non-empty string or array |
tool_result: tool_use_id not found |
Mismatched tool ID | Copy id from the tool_use block exactly |
401 — authentication_error
# Verify your key is set and valid
echo $ANTHROPIC_API_KEY | head -c 15 # Should show: sk-ant-api03-...
# Test directly with curl
curl -s https://api.anthropic.com/v1/messages \
-H "x-api-key: $ANTHROPIC_API_KEY" \
-H "anthropic-version: 2023-06-01" \
-H "content-type: application/json" \
-d '{"model":"claude-sonnet-4-20250514","max_tokens":16,"messages":[{"role":"user","content":"hi"}]}'
403 — permission_error
API key lacks required permissions. Generate a new key at console.anthropic.com.
404 — not_found_error
Invalid endpoint or model. Check you're using https://api.anthropic.com/v1/messages and a valid model ID.
429 — rate_limit_error
{"type": "error", "error": {"type": "rate_limit_error", "message": "Number of request tokens has exceeded your per-minute rate limit"}}
Check headers for details:
retry-after— seconds to waitanthropic-ratelimit-requests-limit— RPM capanthropic-ratelimit-tokens-limit— TPM capanthropic-ratelimit-tokens-remaining— tokens left this window
Fix: The SDK handles 429 with automatic retry (configurable via maxRetries). For manual handling, see anth-rate-limits.
529 — overloaded_error
API is temporarily overloaded. Retry after 30-60 seconds. Not counted against rate limits.
500 — api_error
Internal server error. Retry with exponential backoff. If persistent, check status.anthropic.com.
Quick Diagnostic Script
# 1. Check API status
curl -s https://status.anthropic.com/api/v2/status.json | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['status']['description'])"
# 2. Verify key format
echo $ANTHROPIC_API_KEY | grep -qE '^sk-ant-api03-' && echo "Key format OK" || echo "Key format WRONG"
# 3. Test minimal request
curl -s -w "\nHTTP %{http_code}" https://api.anthropic.com/v1/messages \
-H "x-api-key: $ANTHROPIC_API_KEY" \
-H "anthropic-version: 2023-06-01" \
-H "content-type: application/json" \
-d '{"model":"claude-sonnet-4-20250514","max_tokens":8,"messages":[{"role":"user","content":"1+1="}]}'
SDK Error Handling
import anthropic
try:
message = client.messages.create(...)
except anthropic.AuthenticationError as e:
print(f"Auth failed: {e.status_code}")
except anthropic.RateLimitError as e:
print(f"Rate limited. Retry after: {e.response.headers.get('retry-after')}s")
except anthropic.BadRequestError as e:
print(f"Invalid request: {e.message}")
except anthropic.APIStatusError as e:
print(f"API error {e.status_code}: {e.message}")
except anthropic.APIConnectionError:
print("Network error — check connectivity")
Resources
Next Steps
For comprehensive debugging, see anth-debug-bundle.