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

Annotations only declare readOnlyHint=false and destructiveHint=false, which the append semantics are consistent with. The description adds the genuinely non-obvious behavior: rows are APPENDED and never deduplicated, so re-sending the same list stores it twice. That is exactly the kind of side-effect disclosure annotations cannot carry.

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 sentences, all load-bearing: purpose, workflow relationship, and the append caveat. The purpose and the alternative routing are front-loaded. Minor slack only — the workflow sentence is slightly verbose relative to the rest.

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 mutating batch tool with an output schema present (so return values need no explanation), the description covers purpose, selection, grouping via `label`, and the append/duplicate hazard. It omits the 10,000-item batch cap in `redirects` and any permission/auth expectations, which keeps it short of 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?

With schema coverage at 75%, the schema already explains each field, and the description adds conceptual meaning by defining A as source and B as target and explaining that `label` keeps several migrations apart on one account. It does not add syntax-level detail beyond that, so it lands just above the baseline rather than at the top.

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 gives a specific verb and resource ('Saves redirect mappings (old URL -> new URL) for a site migration') and pins the scope to the source/target property pair. It clearly separates this write tool from compare_migration (the read) and delete_migration_redirects (the clear), so an agent can distinguish it from siblings without opening the schema.

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?

It states when to reach for this tool versus alternatives ('use compare_migration for the before/after performance read, and these mappings to record which old URL became which new one') and names the prerequisite cleanup path ('clear a set first with delete_migration_redirects if you are re-uploading'). Nothing about tool selection is left to inference.

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