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

Annotations already mark this as read-only, idempotent, and non-destructive. The description adds value beyond those by clarifying the data source is the LOCAL message archive and by exposing the per-chat coverage fields and status, which helps the agent understand what the report represents.

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?

Two sentences, with the main purpose front-loaded and the optional parameters compactly listed. Every clause adds useful information and there is no filler, fluff, or repetition of the schema enum/default.

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?

Even without an output schema, the description names the key output fields and explains how the report is used for pagination and backfill decisions. It is reasonably complete for a simple coverage/status tool, though a bit more detail on 'account' and 'status' values would make it fully self-contained.

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 0%, so the description must compensate. It covers the semantics of query (name/JID filter), kind, limit, and chat_jid, but omits the 'account' parameter entirely and gives no detail on how kind/limit interact with the results. The compensation is partial rather than complete.

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 opens with a specific verb and resource: 'Show how far back the LOCAL message archive reaches per chat' and even lists the returned fields (oldest_ts, newest_ts, message_count, status). It clearly distinguishes this from sibling tools by framing it as a coverage/pagination-boundary report rather than message retrieval or archive mutation.

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 explicit usage context: 'Use it to find pagination boundaries for whatsapp_messages and to decide whether to pull more with whatsapp_history_backfill.' It names the related tools and the decision workflow, though it does not explicitly state when not to use it or name direct alternatives.

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