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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely useful context beyond that: the visibility/permission rules that determine success or failure, and an explicit negative scope about external article URLs.

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?

Four short sentences, purpose front-loaded, then access rules, then negative scope. Every sentence carries a distinct constraint; nothing is repeated from the title or schema.

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 single-parameter read tool with an output schema (so return values need no explanation), the description covers purpose, access prerequisites and out-of-scope behavior. An agent has everything needed to call it correctly or recognize a permission failure.

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?

Only one parameter and schema description coverage is 100% — the schema already documents the id and even points at the tools that produce valid IDs. The description's 'by ID' adds nothing the schema does not, so the baseline 3 applies.

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 an existing stream post by ID'), which separates it from the plural list siblings (get_stream_posts, get_collection_posts) and from search_stream_posts. The closing clause 'Does not fetch external article URLs' further fences it off from the generic fetch 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 explicit access conditions: public posts need no following, private posts require individual-post access, and custom-target restrictions still apply. It stops short of naming a sibling to use instead when access fails (e.g. list/search tools), so it is clear context without full routing guidance.

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