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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive. The description adds useful behavioral context beyond annotations: that replies are included, the response is a unified Post, and no API key is required. It does not discuss edge cases like invalid shortcodes or rate limits, but adds meaningful value.

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?

The description is extremely concise, comprising a single sentence plus two short clauses. It front-loads the main action and includes only essential details without unnecessary fluff.

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 simple read-only retrieval tool with strong annotations and fully documented parameters, the description covers the key aspects: what is fetched, how to identify it, and an access requirement ('Keyless'). It does not provide a detailed output structure, but no output schema exists and the tool's simplicity reduces the need.

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 100% and both parameters are already self-explanatory ('Full thread URL', 'Thread shortcode') with the same 'Provide code OR url' guidance. The description repeats this but does not add new meaning such as which parameter to prefer or behavior when both are supplied.

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 uses a specific verb ('Fetch'), identifies the resource (a single thread on Threads by shortcode or URL), and specifies scope ('including its replies, as the unified Post (with replies)'). This clearly distinguishes the tool from siblings like social_posts or social_comments.

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 clear context for use (provide code or URL, keyless access) and implies it is for fetching a specific Threads thread rather than general social posts. However, it does not explicitly name alternative tools or state when not to use this tool.

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