Take a checkpoint

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

Annotations declare destructiveHint=true and idempotentHint=true; the description explains the mechanism behind both with 'a name already taken moves to now', telling the agent that reuse overwrites the prior checkpoint rather than erroring. It also discloses the response ('answers with the checkpoint'). It stops short of stating whether checkpoint creation has any side effects on twin state beyond the name collision.

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?

Two sentences, zero filler. The core definition and its contents come first, the sibling routing follows, and the overwrite caveat closes it out – all in priority order.

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?

For a single-parameter tool with full schema coverage and annotations covering the safety profile, this is nearly complete: it defines the capture, the collision behavior, and the return. Minor gap: given destructiveHint=true, it could say explicitly that the previous checkpoint under that name is lost.

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?

Schema coverage is 100% and already examples the name format ('before-sync'), so the baseline is 3. The description goes beyond that by defining name-reuse semantics and by clarifying that the name refers to a captured moment, not a persistent resource.

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?

States a specific action (name the current moment) and enumerates exactly what gets captured: log position, twin time, and fault dice. It also distinguishes itself from the two siblings that consume checkpoints, twin_changes and twin_rewind, so an agent can tell what this tool is for without opening the schema.

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?

Explicitly names the downstream partners and their conditions: use twin_changes to list changes since, twin_rewind to go back. There is no when-not-to-use or prerequisite guidance, but the routing to alternatives is clear enough to choose correctly.

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