Read mail thread

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

Annotations already declare readOnlyHint=true and openWorldHint=false. The description adds substantial behavioral context beyond this: ordering, message separators, response_format differences ('concise' vs 'detailed'), handling of the 'thread:' prefix, and the caveat about long threads and configured limits. No contradictions with 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?

Every sentence is functional: output format, usage context, alternatives, and parameter details. The structure is clear, front-loaded with the primary purpose, and no redundant wording despite being more detailed than typical.

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 read-only operation with two parameters and no output schema. The description covers output ordering, format, parameter semantics, and usage guidance. It is complete for the tool's complexity and leaves no critical gaps.

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 fully carries parameter documentation. It explains thread_id as 'A thread identifier as returned by mail_search (with or without the 'thread:' prefix)' and response_format with concrete examples of what each option returns. This exceeds baseline for zero-coverage parameters.

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+resource: 'Return every message in a thread, oldest first, with '--- [N/M] ---' separators.' It clearly distinguishes from siblings by explicitly naming mail_read_message for single messages and mail_thread_overview for long threads.

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?

Provides explicit when-to-use ('Use this once mail_search has identified a thread_id'), when-not-to-use ('For a single message, use mail_read_message instead'), and an alternative strategy for long threads ('consider calling mail_thread_overview first'). This fully covers the decision space.

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