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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds that results are newest-first and include a short extract of the last message, which is useful behavioral context beyond the annotations. It doesn't mention pagination behavior explicitly, but the schema covers it.

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, front-loaded with the key behavior (replied threads, newest first, extract) and a clear filter guide, ending with the alternative. Zero waste.

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?

Complete for a read-only filtered list tool whose annotations cover the safety profile. It gives the agent enough to call correctly, though it could mention offset/limit paging semantics, but the schema covers that.

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 coverage is 100%, so the schema documents all parameters. The description still adds semantic meaning to the filter values (e.g., 'needs_reply' = they spoke last and nobody has answered, 'hot' = interested, 'paid' = they quoted a price), which enriches the enum beyond the schema's terse descriptions.

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?

States a specific resource and scope: threads where somebody replied, newest first, with an extract of the last message. Clearly distinguishes itself from sibling list tools like list_pending_drafts and get_thread.

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?

Names the sibling alternative get_thread explicitly for full conversations, and defines each filter value semantically ('needs_reply' = they spoke last and nobody answered, 'hot' = interested, etc.), giving the agent clear conditions for when and how to use it.

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