Single tool with minimal documentation. save_checkpoint has a valid JSON Schema with required fields (thread_id, step, state), but parameter descriptions are absent, only type hints. Tool description is 56 chars, meeting minimum length but lacking actionable context (WHEN to use, WHAT it returns, error recovery). No output schema documented. No error handling guidance. No parameter constraints (enums, ranges). Naming is verb-noun compliant but generic; 'save_checkpoint' doesn't convey domain intent (agent execution recovery, time-travel capability). Missing descriptions for all three parameters violates pattern:tool-description baseline (100% of A+ tools have param descriptions). No mention of idempotency, side effects, or retry safety, critical for a stateful persistence tool.

• Add descriptions to all parameters: thread_id ('Unique identifier for the execution thread, e.g. session_123'), step ('Step index in the execution sequence (integer >= 1)'), state ('Agent execution state object to snapshot; must be JSON-serializable').
• Expand tool description to 150-200 chars: 'Persist a snapshot of agent execution state for time-travel rollback. Call this after each significant step to enable recovery from errors. Returns checkpoint_id for later rollback() or fork_branch() calls.'
• Document output schema in tool definition: {type: 'object', properties: {checkpoint_id: {type: 'string', description: 'Unique checkpoint identifier for use in rollback/fork operations'}}, required: ['checkpoint_id']}.
• Add error handling guidance: 'If thread_id is invalid, returns error with available thread IDs. If state is not JSON-serializable, returns validation error with type hints.'
• Declare idempotency: 'Idempotent: calling with identical thread_id, step, and state produces the same checkpoint_id. Safe to retry on network failures.'