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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds two genuine behavioral facts beyond that: results are ordered oldest first and all metrics live in a single index/response. It says nothing about result caps, pagination, or empty-range behavior, so it does not go beyond the minimum.

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?

A single dense sentence with the resource, granularity, metric list and ordering all front-loaded and no filler. Every clause carries information an agent needs.

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 usefully enumerates the returned metrics and the sort order, which is the key return-value information. It leaves out result-volume limits, pagination, and how to interpret an empty history, so it is nearly but not fully complete for a 4-parameter time-series tool.

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 description coverage is 75%: 'from' and 'to' document their ISO-hour-close format and inclusivity, and 'index' spells out the abi/aii/aei enum meanings. The description adds no parameter meaning at all, and 'id' remains undocumented in both places. With the schema doing most of the work, 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?

The description gives a specific verb-like outcome (hourly points and activity) scoped to a single Arc app and names the concrete metrics returned (payments, paying wallets, new payers, USD). It is clear what the tool produces, but it never names the sibling it is distinct from (arc_app, arc_app_history_deep, arc_index_history), so the agent must infer the hourly-vs-deep distinction.

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?

Usage is implied rather than stated: 'hourly' and 'oldest first' suggest this is the time-series view for one app, as opposed to the summary arc_app or the deeper arc_app_history_deep. There is no explicit when-to-use/when-not-to-use statement or mention of any alternative tool.

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