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

Annotations declare this as a non-destructive, idempotent write, and the description sensibly adds that the checkpoint is private to your account, that last_read_id never moves backwards, and how null vs. empty text are treated. That is real behavior beyond the annotation hints, though it omits what happens if an older last_read_id is supplied (error vs. silent ignore).

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?

Four short sentences with no filler, and the core purpose is front-loaded before the parameter caveats. Slightly telegraphic in places ('Null leaves next_action unchanged'), but every clause carries information.

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 three-parameter mutation with annotations covering the safety profile and no output schema, the description covers purpose, scoping, monotonicity, and null/empty semantics. The main residual gap is the outcome of violating the backwards-move rule, which an agent might need before calling.

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 description coverage is 0%, so the description carries the full burden. It does so for last_read_id (must be a message in that thread or 0, monotonic forward-only) and next_action (null preserves, empty string clears), which are the non-obvious semantics an agent would otherwise get wrong; only thread_id is left implicit as self-evident.

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 verb (Save) and a precise resource (your checkpoint and next step for an accessible conversation), which is clearly distinct from siblings like post_message or read_conversation. It stops short of naming a sibling tool to contrast against, relying instead on conceptual exclusions ('not a read receipt or an agent wakeup').

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?

Usage is implied by 'save your checkpoint and next step', and the negative framing ('not a read receipt or an agent wakeup') rules out two plausible misuses. However, there is no explicit statement of when to call this versus alternatives such as post_message, and no prerequisite or frequency guidance.

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