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

With no annotations, the description carries the burden well: it discloses ownership requirement, behavior on existing members ('silently ignored', i.e. effectively idempotent), behavior across both collection types, and cost ('Free — costs 0 credits'). It omits failure/partial-success behavior and what the call returns.

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 dense sentences: the action first, then the type-dependent semantics, then the edge case and cost. No filler, nothing repeated from the 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 two-parameter mutation with no annotations and no output schema, the description covers the important unknowns (ownership, idempotency, type-dependent effect, cost). The one gap is the absence of any indication of the response shape or error behavior, which an agent might want before bulk-adding up to 1000 posts.

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%, so post_ids (1-1000 UUIDs) and collection_id (from list_collections) are already documented in the schema. The description reinforces the post_id intent and adds no format, ordering, or dedup detail beyond that, so 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?

Specific verb ('Pin') plus resource ('one or more posts into a collection') with the scoping condition 'a collection you own — works on any collection type.' It clearly separates itself from nearby tools like add_to_segment and create_collection by naming the membership semantics.

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?

Explicitly explains the manual-vs-smart distinction and that this is the *only* membership mechanism for manual collections, and it points at resolve_collection for seeing the union. It does not explicitly say when to prefer add_to_segment or create_collection instead, so it stops short of full alternative routing.

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