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

With readOnly/idempotent annotations already covering the safety profile, the description still adds real behavior: a hard coverage floor of 2026-08-31, the entry shape (from → to, effectiveFrom, source, verifiedDate, maintainer note), and the Verified Changes protocol doc plus human-facing URL/feeds. It does not state what an out-of-range `since` returns, but the substantive additions are well above the annotation baseline.

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?

The purpose is front-loaded and the tail (coverage start, output protocol, sibling linkage) earns its place, but the middle is a single ~200-word run-on enumeration of dozens of dataset names and jurisdictions. That list helps coverage assessment yet is far denser than needed and would be better grouped or left largely to the area enum.

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 read-only changelog tool with no output schema, the description covers return shape (entry fields, protocol, factKey), coverage boundaries, and downstream tool routing. The only gap is undefined behavior for dates before the coverage floor or an invalid/earlier-than-supported `since`.

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 `area` enum is fully documented in the schema, so the description's repetition of the area list is redundant rather than additive. The one genuine addition is guidance that `since` should be your training cutoff, which clarifies intent beyond the schema's 'ISO date YYYY-MM-DD' — baseline 3 with a small bump, still not more.

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 ('what has changed ... since a date') and immediately scopes it to Data Butler's verified datasets, then enumerates exactly which dataset families are covered. An agent can decide coverage without opening the schema, and the closing mention of get_fact for factKey lookups separates it from its siblings.

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?

'Pass your training-cutoff date to learn which ... changed after your knowledge ends' gives a concrete usage trigger and even the intended value for `since`. It also signals the handoff to get_fact for individual facts, but it never says when NOT to call it (e.g. a date before the 2026-08-31 coverage floor, or use get_fact/resolve_fact for a single known figure).

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