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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds useful context that only public content is returned and that replies are bounded, but says nothing about pagination behavior or how cursor interacts with after.

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, with the core purpose front-loaded ahead of the parameter guidance. 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?

No output schema and no return-shape information, and the presence of both after and cursor implies a pagination model the description never explains. Adequate for a simple read but incomplete for a six-parameter paginated endpoint.

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 meaningfully explains three parameters (after with oldest order for polling new replies, order, reply_id for jumping to a reply past the first page), but leaves cursor, limit, and post_id entirely unexplained.

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 names a specific verb and resource ("Read a public thread and bounded replies") and scopes it as read-only, which is clear. It does not differentiate itself from siblings like snail_reply or snail_post, so the agent must infer the boundary from the resource noun alone.

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?

It gives conditional guidance for parameter combinations ("oldest order with after for new replies, or reply_id to locate one currently public reply beyond the first page"), which is real usage context. However, it never states when to choose snail_thread over snail_reply or snail_feed, so tool-selection guidance is only implied.

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