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

Beyond the readOnlyHint=true annotation, the description adds valuable behavioral detail: pagination via after_cursor, the need to loop until has_more is false, and that each call indicates whether it was answered and its duration. It also notes the ordering (oldest first). These details are not in the annotations and significantly inform the agent's invocation strategy.

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 two sentences with no fluff. The primary purpose is front-loaded in the first sentence, and the second sentence efficiently covers pagination and output characteristics. Every sentence earns its place; there is no redundant or extraneous information.

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?

The tool is a simple read-only list with optional parameters and an output schema. The description covers the core usage (what it returns, ordering, pagination) and the schema documents all parameters. There are no complex side effects or prerequisites to disclose. The description is complete for an agent to call the tool correctly, especially with the output schema available.

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 input schema already describes all three parameters with 100% coverage, giving a baseline of 3. The description adds extra meaning for after_cursor by explaining the pagination loop ('pass back the next_cursor... keep going until has_more is false'), which is not present in the schema. It does not elaborate on limit or account_id, but those are already well-documented, so the added context justifies a score above baseline.

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: 'Read call history across your WhatsApp accounts, oldest first.' This distinguishes it from sibling list tools like wa_list_messages or wa_list_contacts, which focus on different data types. The scope (across accounts) is explicit, leaving no ambiguity about what the tool retrieves.

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 provides clear context for the tool's purpose and how to use it (pagination pattern), but it does not explicitly mention alternatives or when not to use it. The distinction from sibling list tools is implied by the resource type, but no explicit exclusion or alternative routing is given. This is 'clear context, no exclusions' per the rubric.

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