index_stats

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

With no annotations, the description carries the full burden, and it does disclose what information is returned (size, date range, last sync). It never states that this is a safe read with no side effects, nor does it mention permissions or whether the account must be synced first.

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 compact fragment that front-loads the three returned fields with no filler. It is a noun phrase rather than a sentence, which is slightly terse but entirely efficient.

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?

There is no output schema, so the description usefully enumerates the returned fields, and the only parameter is optional and schema-documented. However, it gives no indication of behavior on missing/unsynced accounts or any usage context, leaving modest gaps for a stats 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 100% and the single 'account' parameter is fully documented in the schema, so the description adds no meaning beyond it. Baseline 3 is appropriate when the schema does the work.

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 names the specific resource (local mail index) and exactly what it reports: size, date range, and last sync time. That distinguishes it from siblings like sync_index and search_index, though it omits an explicit verb (e.g., 'return' or 'report').

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?

There is no guidance on when to call this versus sync_index or search_index, and no stated prerequisites. The read-only nature is inferable from 'stats', but nothing is said explicitly.

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