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

Annotations mark this as a non-destructive, idempotent, non-read-only write, and the description adds genuinely useful context beyond them: the call consumes one of the month's coverages (or a purchased one), and the model is then maintained every night. It stops short of stating what happens when no coverage remains, what the response contains, or whether repeated calls on the same id consume additional coverages.

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?

Two front-loaded sentences with the core action first and the quota cost second; every clause carries information. The parenthetical '(or keeps working the one it has)' is slightly wordy but clarifies idempotent re-covering.

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 one-parameter, quota-consuming write with no output schema, the description covers the essentials of what happens and what it costs. It omits failure modes (exhausted coverages, invalid or already-covered id) and what the caller should expect back, leaving gaps an agent would hit on first use.

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% and the single 'id' parameter already documents all three accepted formats (ch: model id, datasnack.ai/m/ URL, market id from search_models). The description adds nothing about the parameter, so the 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?

States a concrete verb and resource ('Cover a market for the signed-in reader') and immediately explains the resulting behavior: DataSnack builds or maintains a model nightly and the reader can export it to Excel. It is clearly distinguishable from read-only siblings like cover_status or get_model, though no sibling is named explicitly.

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?

Implies the precondition (the reader must have a monthly coverage in their plan or have bought one), which tells the agent when the call will succeed. However, it never says when NOT to use it, nor points to alternatives such as cover_status for checking existing coverage or follow_model for a non-consuming option.

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