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

Beyond the readOnlyHint and idempotentHint annotations, the description discloses that reading does not mark anything as read, that quoted copies are trimmed unless includeQuoted is set, that bodies are plain text only, and that thread completeness depends on the References header. These are valuable behavioral details not present in the annotations.

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 long but every sentence carries a distinct operational concern: one-call efficiency, alternative tool routing, default mailbox scope, no-read side effect, quote trimming, plain-text limitation, and thread completeness caveat. The core action is front-loaded and the structure is dense without being redundant.

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?

Given that there is no output schema, the description compensates by explaining the important return behaviors: oldest-first ordering, quotedTrimmed flag, plain-text bodies, and the possibility of a shortened thread. Combined with the annotations and fully documented parameters, it gives an agent enough to invoke the tool and interpret results correctly.

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?

The schema already covers 100% of parameters, so the baseline is 3, but the description adds useful nuance: the UID can be any message in the conversation, mailboxes defaults to the message's folder plus Sent, naming mailboxes replaces that default, and includeQuoted can multiply result size. This is meaningful enrichment beyond the schema.

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 states a specific verb and resource: 'Read an entire email conversation in ONE call, oldest message first, given any one message in it.' It clearly distinguishes itself from read_email and search_emails by emphasizing the whole-thread scope and the one-call behavior.

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?

It explicitly tells the agent when to prefer this tool: 'USE THIS INSTEAD OF CALLING read_email REPEATEDLY' and gives a concrete user-intent example ('catch me up on this thread'). It also names the fallback case: use read_email when HTML or a full untrimmed body is needed, and warns about incomplete threads when the References header is absent.

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