Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations indicate readOnlyHint=false and destructiveHint=false, so it is a non-destructive write. The description adds a critical behavioral constraint: 'The cursor only ever moves forward, and only to a value you were actually handed,' which prevents arbitrary cursor setting and implies monotonic progress. However, it does not disclose whether an existing checkpoint is overwritten, any size limits, or what the response contains. Given the minimal annotations, the description carries some burden but leaves gaps.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is compact—three sentences—and front-loads the three key items (focus, note, cursor). The advisory 'Write it while you still can' conveys urgency without being verbose. The final sentence about the cursor is a bit cryptic but still adds value. No fluff or repetition, though the poetic tone could be clearer for a technical tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has no output schema and minimal annotations, so the description must explain behavior. It communicates that the checkpoint outlives the session and that the cursor is monotonic. However, it does not mention how the saved data will be retrieved (e.g., via 'resume'), whether multiple checkpoints are allowed, or error conditions. For a state-saving tool, this leaves some ambiguity about the lifecycle and integration with sibling tools, making it only partially complete.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema already covers all parameters with descriptions at 100% coverage. The description maps 'how far you have read' to the cursor parameter, reinforcing schema meaning. It also adds the cursor monotonicity constraint, which is not in the schema. This goes slightly beyond the schema, but the added value is modest; the description does not provide examples or additional format hints. A baseline of 3 is appropriate given the high schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states it saves focus, a note to self, and progress (cursor). It clearly identifies the resource being written and the three pieces of state. It does not explicitly differentiate from siblings like 'resume' or 'agent_heartbeat', but the title and phrasing make the checkpoint concept clear. The metaphor 'save your place' adds context without being a tautology.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description advises writing the checkpoint 'while you still can, not when your context is nearly gone,' which is a timing guideline. However, it does not mention when not to use it or contrast with alternatives such as 'resume' or 'agent_heartbeat'. The usage context is implied (to persist state for future sessions) but no explicit exclusions are provided.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.