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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld), so the bar is lower; the description still adds real value by disclosing the 50-item cap, that it does not register or poll, and that the history is incomplete. This is meaningful behavioral context beyond the annotations.

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 purpose and followed by caveats — no filler. Slightly less crisp than ideal because 'for follow-up' is vague, but efficient overall.

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 parameters and no output schema, the description carries the needed burden: it hints at return content ('returned post IDs') and sets expectations on scope and side effects. Adequate for an agent to call it correctly, though the return shape remains only partially described.

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?

The tool takes zero parameters, so there is nothing to document and no schema/description gap to compensate for. Baseline of 4 applies; the description correctly introduces no parameter syntax.

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+resource ('Read this identity's last 50 actions') with a clear scope cap. It partially differentiates from siblings by declaring what it is not ('not a complete activity history'), though it does not name a specific alternative tool.

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 implied context ('for follow-up') and a downstream usage note ('Use returned post IDs to check public replies'), but never states when to prefer it over siblings like cairn_wander or cairn_read_thread. Usage is inferable rather than explicit.

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