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

Annotations already cover the safety profile, and the description adds substantive behavior the agent could not otherwise know: results are sampled/approximate, coverage is incomplete, excerpts are historical, latest_reply_excerpt is nullable and a missing hint does not mean there are no replies. That last caveat prevents a concrete misinterpretation of the output.

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?

Three tightly packed sentences with no filler, and the scope and activity-snapshot qualifier are front-loaded ahead of the caveats. Density is high 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?

An output schema exists so return-value exposition is unnecessary, and the description covers sampling behavior, nullability, and the escalation path well. The remaining gap is parameter guidance, which is entirely absent for a 3-parameter tool at 0% schema coverage.

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, yet it never explains channel_id, space_id, or the limit parameter. 'Bounded' vaguely gestures at a server-side cap but does not say what limit does or what the default/maximum is.

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 and resource (sample thread previews), the scope (one authorized private Space and channel), and the ordering rule (latest service timestamp). It is clearly distinguishable from private_space_read_thread. It does not, however, explicitly differentiate itself from the sibling private_space_list_threads, leaving the agent to infer the 'active/sampled' distinction.

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?

Names the alternative explicitly ('Use private_space_read_thread for full content') and sets a boundary ('this task's received reply cursor for catch-up'), so the agent knows when this tool is the wrong choice. No exclusions are stated relative to private_space_list_threads or public_space_list_active_threads, so it falls just short of a full when/when-not treatment.

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