Claude Code Explore Subagent Fails with 400 Invalid JSON Schema on Every Dispatch

What this error means

tools.153.custom.input_schema: JSON schema is invalid is a Claude Code failure pattern reported for developers trying to fix claude code explore subagent 400 error json schema is invalid. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

Every dispatch of the built-in Explore subagent (via Agent tool with subagent_type: ‘Explore’) is rejected by the Anthropic API with 400: tools.153.custom.input_schema: JSON schema is invalid. Must match JSON Schema draft 2020-12.

Common causes

• The built-in Explore subagent is broken for many users — every dispatch fails with a 400 error. This blocks a core feature of Claude Code that developers rely on for codebase exploration.
• Every dispatch of the built-in Explore subagent (via Agent tool with subagent_type: ‘Explore’) is rejected by the Anthropic API with 400: tools.153.custom.input_schema: JSON schema is invalid. Must match JSON Schema draft 2020-12.

Quick fixes

1. Confirm the exact error signature matches tools.153.custom.input_schema: JSON schema is invalid.
2. Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
3. 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

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. 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

• https://github.com/anthropics/claude-code/issues/59354

Evidence note: Every dispatch of the built-in Explore subagent (via Agent tool with subagent_type: ‘Explore’) is rejected by the Anthropic API with 400: tools.153.custom.input_schema: JSON schema is invalid. Must match JSON Schema draft 2020-12.

Related errors

• Claude Code tool call validation error
• Anthropic API tools parameter rejected

FAQ

What should I check first?

Start with the exact tools.153.custom.input_schema: JSON schema is invalid text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Claude Code 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 tools.153.custom.input_schema: JSON schema is invalid.