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

Annotations cover the safety profile (readOnlyHint, openWorldHint), so the bar is lower. The description adds genuinely useful behavior: the hasMore/nextCursor loop, which is an output-side contract that would otherwise be invisible since there is no output schema.

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 short sentences, front-loaded with the purpose and then the two usage paths and pagination rule. No filler and nothing buried.

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?

With no output schema, the description helpfully discloses the pagination fields (hasMore, nextCursor), and annotations cover safety. It is nearly complete; minor gaps remain around result shape (e.g., ordering, whether the parent message is included).

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 each parameter is documented in the schema, so the baseline is 3. The description restates the two invocation modes (link vs channel+ts) and the cursor usage but adds little syntax or format detail beyond what the schema already provides.

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 ('Read a message and its thread replies'), which is precise and clearly thread-scoped. It does not explicitly name how it differs from the sibling read_messages, but the thread-reply scope is a strong implicit differentiator.

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?

Gives concrete invocation paths: a message link, or a channel plus parent ts, plus the continuation rule for pagination. No exclusions or comparison to read_messages/search_messages is offered, so it stops short of a 5.

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