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

Goes well beyond the annotations (which only say non-read-only, idempotent, non-destructive, open-world). It discloses that new extensions are unattached and won't serve, that character limits are validated first, that descriptions must be supplied together or not at all, that callouts need at least 2 to serve, and that dryRun previews without sending anything.

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?

Purpose is front-loaded, followed by attachment behavior, validation limits, serving rule, and dryRun hint. Every sentence carries distinct information with no redundancy.

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?

With no output schema, the description covers what is created, its unattached state, the follow-up tool, constraints, and preview mode. The one gap is the return value – an agent isn't told whether extension IDs come back, which matters for the subsequent attach call.

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?

At 75% schema coverage the schema documents most params, but the description adds rules not present in it: sitelink text 25 characters (35 without descriptions), descriptions up to 35 and paired, callout text 25. It doesn't add anything about accountId, which the schema already explains.

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?

Opens with a specific verb and resource: 'Create sitelinks and/or callouts in the account's extension library.' It also distinguishes itself from the attach tool by stating the extensions are created UNATTACHED and naming msads_set_ad_extension_attachment as the step that makes them serve, so an agent can separate this from sibling extension tools without reading schemas.

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?

Gives clear operating context: create here, attach later with msads_set_ad_extension_attachment, and 'Use dryRun to review.' It doesn't explicitly rule out the sibling add_callouts/add_sitelinks tools or state prerequisites like account selection, so it stops short of full when/when-not guidance.

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