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

With no annotations, the description carries the full burden and delivers: keyset pagination and ordering, a dated behavior change for tag vs imported_tags, the include_count 503 count_unavailable error (never 0), and the smart-list zero-row quirk. These are non-obvious behaviors an agent could not infer from the schema.

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?

Front-loaded with the core action and pagination model, then filters. It is a dense single paragraph where nearly every clause earns its place, though the tag-date clause is heavy for one sentence.

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?

With no output schema, the description partially compensates by naming returned fields (tags, catalog_tags, total_count) and the cursor. It omits other row fields and rate/auth considerations, but is sufficient for correct invocation.

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 83%, yet the description adds meaning beyond it: list_id is physical membership only, tag matches the exact catalog name with the imported_tags/catalog_tags distinction, and include_count's failure mode is spelled out. This is substantive enrichment, not repetition.

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 (list paginated contacts) plus ordering (most recent first, keyset cursor). It differentiates from siblings by routing smart-list size lookups to list_lists, so an agent can place it precisely.

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 clear context for each filter and a strong edge-case rule: list_id returns 0 rows for smart lists, whose size lives in list_lists. It stops short of naming a when-not or explicit alternatives beyond the count pointer, so it is strong but not exhaustive.

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