Claude Code / AI Coding Tools

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

Fix Claude Code Explore subagent 400 error JSON schema is invalid Includes evidence for Claude Code troubleshooting demand.

Source-backed Last updated May 15, 2026 1 source Needs local verification

Category: AI Coding Tools
Error signature: tools.153.custom.input_schema: JSON schema is invalid
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 15, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for Claude Code, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

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

Confirm the exact error signature matches tools.153.custom.input_schema: JSON schema is invalid.
Check the Claude Code 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.

Diagnostic flow for this page

Match tools.153.custom.input_schema: JSON schema is invalid exactly before applying the quick fix.
Compare the failing environment with Claude Code versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does tools.153.custom.input_schema: JSON schema is invalid mean in Claude Code?

tools.153.custom.input_schema: JSON schema is invalid indicates the workflow described by "Claude Code Explore Subagent Fails with 400 Invalid JSON Schema on Every Dispatch" failed in a AI Coding Tools context. Start by confirming the exact signature and the component that emitted it.

What should I check first for tools.153.custom.input_schema: JSON schema is invalid?

Check whether this cause matches your environment: 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.

Is the tools.153.custom.input_schema: JSON schema is invalid guidance source-backed?

The "Claude Code Explore Subagent Fails with 400 Invalid JSON Schema on Every Dispatch" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for tools.153.custom.input_schema: JSON schema is invalid?

For "Claude Code Explore Subagent Fails with 400 Invalid JSON Schema on Every Dispatch", avoid applying "Compare the failing environment with a known working setup, then change one configuration value at a time." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging tools.153.custom.input_schema: JSON schema is invalid?

For "Claude Code Explore Subagent Fails with 400 Invalid JSON Schema on Every Dispatch", collect the failing Claude Code command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.