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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds real value beyond that by disclosing the wrapper it delegates to (branch-previews.getPreviewForBranch) and the exact failure envelope {ok:false, reason:'not enabled on this host'}, which tells the agent how to interpret a non-result. It stops short of describing the success payload shape beyond 'URL + status'.

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?

Three short sentences with zero filler: purpose first, implementation second, failure mode third. Every sentence contributes distinct information and nothing is repeated from the title or annotations.

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 read-only lookup with no output schema, the description covers purpose, delegation target, and the no-preview-host failure case, which is what an agent needs to call and interpret it. The remaining gaps are the undocumented owner parameter and the success return shape, both minor relative to the tool's simplicity.

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 must carry the full burden for three required parameters. It names only repo and branch as a key pair and says nothing about owner (required but unmentioned), nor about formats such as repo slug vs. name or branch naming conventions. The gap leaves one parameter entirely unexplained and adds little meaning beyond the schema's property names.

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: 'Return the branch-preview URL + status for a (repo, branch) pair.' No sibling tool covers preview URLs, and the description names the underlying capability explicitly, so an agent can identify the tool's job immediately.

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 usage by defining the lookup (get preview URL for a repo/branch) and explains one negative condition, the host lacking PREVIEW_DOMAIN. It gives no explicit 'use this when' framing, no prerequisites, and no comparison to any alternative path for obtaining a preview link.

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