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

Annotations only cover safety (readOnly, idempotent, non-destructive, closed-world); the description adds substantial behavior beyond them: parallel reads from multiple home IPs in the target country, a ~70-second ceiling, higher credit cost, the meaning of seen_in and best_position, sort order (most-seen first), and the complete=false condition. That is exactly the operational detail an agent needs before committing to an expensive call.

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 outcome (what you get), then mechanism, then return-field semantics, then cost/latency warning. Dense but nearly every clause carries information; the trailing 'because it makes many' is mildly redundant with the earlier parallel-read explanation.

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 fully carries the return-value burden: it names the per-card fields (seen_in, best_position), the ordering, and the complete flag, and it discloses cost and latency for an expensive operation. Nothing an agent needs to decide or call correctly is missing.

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 the baseline of 3 already applies, and the description adds real meaning: the cards count is a target for distinct cards that stops early when the pool runs dry, and country determines which home IP the feed is read from, shaping the stories returned. It does not add format details beyond what the schema already states.

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 first sentence gives a specific verb and resource (collect Discover cards) plus scope (up to 300 different cards in a country, with appearance counts). It implicitly contrasts with a single feed read ('One read of the Discover feed holds about 31 cards'), but never names the sibling get_discover_feed, so separation is inferred rather than explicit.

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?

Clear context for when to pick this over a plain read: it reads many times in parallel until the requested number of distinct cards is reached or the pool is exhausted, and it warns that a call takes ~70 seconds and more credits. Missing an explicit 'use get_discover_feed instead when you only need one read' routing statement.

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