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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), and the description adds substantial behavior beyond that: changes are derived by diffing consecutive constituent lists, dated to reporting windows rather than announcements, and de-duplicated across funds by keeping the narrowest window. It also flags that additions carry an estimate rather than a record of implied fund buying, which is a meaningful caveat not expressed anywhere in structured fields.

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 in the first sentence and each subsequent sentence contributes distinct information (derivation, dating granularity, de-duplication, estimate caveat). The middle de-duplication sentence is fairly sprawling and could be tightened, but nothing is pure filler.

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 does well to imply the shape of a change record (company, direction, window, implied buying in shares and days of volume). It does not spell out the concrete response fields or pagination/truncation behavior for maxResults, which leaves a modest gap for a two-parameter read tool with no output schema.

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 100%, so both parameters (index format, maxResults default/max) are already fully documented in the schema. The description adds no format hints, slug conventions, or guidance beyond what is structured. Baseline 3 is appropriate when the schema does the heavy lifting.

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?

It states a specific verb and resource ('companies that have joined or left a major US stock index') and adds an ordering guarantee ('newest first'). This clearly distinguishes it from siblings like GetIndexComposition (current membership) or GetIndexForecast, so an agent can route without opening a schema.

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?

The description gives strong context on what the data represents and explicitly excludes a competing reading ('This is observed membership, not an announcement feed'), which is effectively a when-not statement. However, it never names an alternative sibling tool for the announcement-style or point-in-time-membership use cases, so routing is left partly to inference.

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