API Error 400: text content blocks must contain non-whitespace text

Bug Report

Error

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages: text content blocks must contain non-whitespace text"},"request_id":"req_011CXqXVfVqMJd8rzkVKPZDM"}

Description

Claude Code throws a 400 error from the Anthropic API indicating that a text content block with empty or whitespace-only content was sent in a message.

Error Details

• HTTP Status: 400
• Error Type: invalid_request_error
• Message: messages: text content blocks must contain non-whitespace text
• Request ID: req_011CXqXVfVqMJd8rzkVKPZDM

Expected Behavior

Claude Code should validate that all text content blocks contain non-whitespace text before sending requests to the API. Empty or whitespace-only blocks should be filtered out or replaced with meaningful content.

Possible Causes

• A tool returning an empty result that gets included as an empty text block
• Context compaction leaving an empty text block
• A hook returning a blank response

Environment

• Platform: Windows
• Date: 2025-02-05
• Model: claude-opus-4-6