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

Annotations already cover readOnly, idempotent, non-destructive and closed-world, so the description focuses on what annotations can't express: the data comes from an OAuth-selected session with expiry, and it returns no raw messages, names, excerpts, paid insights, or newly computed analysis. That negative-boundary disclosure is genuinely valuable, though it partially restates the output payload that the output schema already defines.

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 positive scope, then exclusions, then a concrete example, then return contents. Dense and purposeful, but the example block and the repeated 'cannot answer / explain unavailability' phrasing cover overlapping ground and could be tightened.

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 single-parameter read tool with full annotations and an output schema, the description covers authorization source, scope limits, unsupported request handling, and the negative data boundaries. Nothing an agent needs to decide whether and how to call it 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 0% for the single locale parameter, so the description must compensate; it does so with 'Set locale to the user's supported language,' which clarifies the parameter governs response language and implies constraint to the supported set (the enum lists six locales). It stops short of naming defaults or fallback behavior, but the enum carries that.

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 ('retrieve or explain WHOLE-SESSION numerical statistics') and immediately bounds the scope to stored whole-session totals from an authorized export analysis. The agent can distinguish this from period-comparison style tools without opening the 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?

Explicitly names when not to call ('DO NOT call for date-window, month-to-month, trend or period-comparison requests, even to check available data') and prescribes the alternative behavior: explain the capability is unavailable. A concrete worked example ('Compare September and November...') removes all inference.

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