Anthropic API / Anthropic API
Anthropic API 400: text content blocks must be non-empty error fix
Fix Anthropic API 400 error when text content blocks are empty in messages.create request Includes evidence for Anthropic API troubleshooting demand.
- Category
- Anthropic API
- Error signature
API Error: 400 messages: text content blocks must be non-empty- Quick fix
- Compare the failing environment with a known working setup, then change one configuration value at a time.
- Updated
What this error means
API Error: 400 messages: text content blocks must be non-empty is a Anthropic API failure pattern reported for developers trying to fix anthropic api 400 error when text content blocks are empty in messages.create request. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.
Why this happens
Production error on TradeMindAI (PR #295): Anthropic API rejects requests with empty text content blocks. Caused by incorrect cache_control block shape change in system prompt and tool schema. The error appears when messages array contains text blocks with empty content. Category mapped directly to Anthropic API per approved list.
Common causes
- Production error on TradeMindAI (PR #295): Anthropic API rejects requests with empty text content blocks. Caused by incorrect cache_control block shape change in system prompt and tool schema. The error appears when messages array contains text blocks with empty content. Category mapped directly to Anthropic API per approved list.
Quick fixes
- Confirm the exact error signature matches
API Error: 400 messages: text content blocks must be non-empty. - Check the Anthropic API account, local tool state, and provider configuration involved in the failing workflow.
- Compare the failing environment with a known working setup, then change one configuration value at a time.
Platform/tool-specific checks
- Verify the command, editor, extension, or API client that produced the error.
- Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
- Avoid deleting credentials, local model data, or project settings until the failing scope is clear.
Step-by-step troubleshooting
- Capture the exact error message and the command, editor action, or request that triggered it.
- Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
- Review the source evidence below and compare it with your environment.
- Apply one change at a time and rerun the smallest failing action.
- Keep the working fix documented for the team or deployment environment.
How to prevent it
- Keep provider/tool configuration documented.
- Record non-secret diagnostics such as tool version, provider name, model name, and command path.
- Add a lightweight check before CI or production workflows depend on the tool.
Sources checked
Evidence note: Production error on TradeMindAI (PR #295): Anthropic API rejects requests with empty text content blocks. Caused by incorrect cache_control block shape change in system prompt and tool schema. The error appears when messages array contains text blocks with empty content. Category mapped directly to Anthropic API per approved list.
Related errors
- Anthropic API
FAQ
What should I check first?
Start with the exact API Error: 400 messages: text content blocks must be non-empty text and the smallest action that reproduces it.
Can I ignore this error?
No. Treat it as a failed Anthropic API workflow until the root cause is understood.
Is this guaranteed to have one fix?
No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.
How do I know the fix worked?
Rerun the same command, editor action, or request. The fix is working when that action completes without API Error: 400 messages: text content blocks must be non-empty.