substack_search

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

With no annotations provided, the description carries the full burden. It discloses that the tool searches across all of Substack, returns matching publications, and optionally returns focused_posts when focus_publication_id is set. This goes beyond a simple 'search' statement and explains the output shape, though it does not cover pagination or other runtime behavior. The described behavior is consistent and non-misleading.

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 three sentences: the primary purpose, the key differentiator, and the optional parameter behavior. It is front-loaded with the core action and scope, with no filler or redundant content. Every sentence serves a distinct purpose.

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?

Given the tool's complexity (4 parameters, search over a large corpus) and no output schema, the description covers the core behaviors: site-wide vs focused search, result types, and the function of optional parameters. It does not mention sorting or additional output fields, but it provides enough for an agent to invoke it correctly and understand what to expect. The lack of an output schema is partially mitigated by describing the focus behavior.

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% with parameter descriptions already present, so baseline is 3. The description adds meaning beyond the schema by explaining the relationship between focus_publication_id and focused_posts, and clarifying that focus_limit caps those results. This provides agent-relevant context not present in the schema alone.

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 states a specific verb ('Search'), a clear resource ('posts and publications across Substack'), and explicitly differentiates from the sibling tool /substack/publication/posts. It conveys the scope (site-wide vs single publication) and the dual result nature (posts and publications), making the tool's purpose unambiguous.

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 explicitly contrasts with /substack/publication/posts, clarifying when to use this tool (site-wide search) vs the alternative (single-publication search). It also explains the optional focus_publication_id and its effect on results, giving an agent clear conditional guidance without leaving inference to the reader.

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