Open a local email archive

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

With no annotations, the description carries full transparency burden. It discloses key behaviors: 'entirely locally, nothing leaves the machine' (privacy), returns 'message count, date range, and top senders', and 'Large archives are indexed once and cached'. It doesn't detail side effects like where the index/cache is stored, but provides meaningful behavioral context.

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 description is three concise sentences, each adding distinct value: input formats + privacy, return values, and caching behavior. It is front-loaded with the core purpose and contains no wasted words.

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 tool with one required parameter and no output schema, the description is remarkably complete. It covers input types, local processing guarantee, summary statistics returned, and caching behavior. No critical gaps for the tool's simplicity.

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 'path' parameter is fully described in the schema. The description restates similar information ('.mbox file' and '.eml' directory) but adds no new parameter semantics beyond what the schema already provides. Baseline 3 is appropriate.

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 uses a specific verb 'Index' with a clear resource: '.mbox file' or 'directory of .eml files'. It distinguishes itself from sibling tools (search_messages, get_message) by focusing on loading/opening an entire archive rather than retrieving individual messages.

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 implies when to use this tool: to index an email archive for local processing. It provides clear context (supports Google Takeout and Thunderbird exports) but does not explicitly contrast with siblings or mention when not to use it. No exclusions or alternative tool names are given.

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