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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds one genuinely non-obvious trait — 'Costs 1 credit' — but says nothing about result limits, pagination, or how far back the public index reaches, which matters for a search tool.

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 fragments, front-loaded with the core action and with the cost note at the end where it belongs. The second sentence largely restates the first ('posts by keyword' vs 'posts matching a keyword'), which is minor redundancy.

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 exists, yet the description says nothing about what a result contains, how many are returned, or how to page through them. Combined with the undocumented cache_max_age parameter, an agent cannot predict response behavior before spending a credit.

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 only 50%: 'query' is documented but 'cache_max_age' has no description anywhere. The description does not explain the cache parameter's format or effect, so it fails to compensate for the coverage gap.

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 (search) and resource (public Threads posts matched by keyword), which separates it from threads_searchUsers and threads_userPosts by resource type. It never names the sibling alternatives explicitly, so differentiation comes from the name rather than the text.

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?

No when-to-use or when-not-to-use guidance, and no mention of the obvious alternatives (threads_searchUsers for people, threads_userPosts for a known account's timeline). The only implicit scoping is 'public' posts, which the agent has to infer.

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