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

Adds real behavioral context beyond destructiveHint=false: it explains the comment's position in the thread (opening comment vs reply), its visibility in the viewer, and that it does not trigger automations. It stops short of stating permission requirements, whether edits/deletes are possible, or what the call returns.

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, correctly front-loaded with what the tool does, followed by the two non-obvious behavioral facts. Nothing is redundant with the title and no sentence is filler.

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?

For a simple four-required-param mutation with no output schema and minimal annotations, the description covers the key semantics (thread placement, visibility, automation side effect). Only the lack of any hint about the response or about failure modes keeps it from being complete.

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 100%, so all four parameters are already documented in structured fields. The description only reinforces the doc/annotation relationship conceptually and adds no format or constraint detail beyond the schema, so baseline 3 applies.

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 verb and resource ('Add a comment to an annotation on a document') and clearly separates it from sibling annotation-listing tools. An agent can tell immediately this is a write-to-thread operation, not an annotation creation tool.

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 implies the workflow because the schema references list-document-annotations for annotation_id, but the description itself gives no explicit when-to-use, prerequisites, or exclusions relative to other comment/annotation tools. Usage must be inferred.

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