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

Annotations already supply destructiveHint, idempotentHint and openWorldHint=false, so the safety profile is covered structurally. The description adds genuinely non-obvious context beyond that: the effect is deferred ('stops using it on its next replies') and the site's login credential survives deletion for the site's other and future tools. It does not cover auth/permission requirements, but the added semantics are substantive.

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?

Compact and front-loaded, with the destructive effect and the credential-retention caveat stated up front. It loses a point because the opening line merely restates the title before the actual content, and the final sentence's phrasing ('for the site's other tools and the next one') is slightly compressed.

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 two-parameter destructive tool with full annotation coverage and complete schema parameter documentation, the description covers what an agent needs: what is destroyed and what is preserved. It lacks any note on whether deletion is reversible or requires elevated permissions, which is the main remaining gap.

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%, and both parameters carry rich descriptions including the exact error semantics (404 not_found, 404 agent_not_found, 403 agent_not_authorized). The description adds nothing further about tool_id or agent_id, so the 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?

The description pairs a specific verb ('Delete') with a specific resource ('custom API tool'), and the title/name match reinforces it. Among the many delete_* siblings, the resource noun alone makes it unambiguous which entity is destroyed.

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?

There is no statement of when to delete versus when to use an alternative such as update_custom_api_tool to disable the tool, nor any prerequisite/permission guidance. The closest thing is a consequence statement ('the AI stops using it on its next replies'), which describes an effect rather than a selection criterion.

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