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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint, so the safety profile is covered and the description's restatement of 'read-only and idempotent' is mild redundancy. It does add genuinely new behavior: idempotency holds only until the health probe changes, the response carries a 6-hourly probe plus invocation details, and an unknown/unapproved slug is an error rather than an empty result.

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?

Front-loads the core action and the precondition before the alternatives, and every sentence carries routing or error information. The middle sentence enumerating returned fields (endpoint, auth mode, pricing, health probe, etc.) is the longest and is partly redundant given an output schema exists.

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 single-parameter lookup with full annotation coverage and an output schema, this covers everything an agent needs: what it returns, why it differs from listing tools, when not to use it, and the failure mode for a bad slug. Nothing material is missing.

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 the slug schema is already rich (case-sensitivity, length, approved-only), so baseline is 3. The description adds usage-level meaning the schema does not: the slug should come from a prior tool result rather than being guessed, and only approved entries resolve. It stops short of adding format or validation detail beyond the schema.

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 ('Fetch the full record of ONE approved registry entry'), scopes it to an exact slug, and explicitly positions it as the single-record lookup that takes no filters or paging. An agent can distinguish it from search_registry, discover_capabilities and list_entries without opening any 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?

Gives an explicit precondition ('whose exact slug you already have'), names where the slug comes from, and routes the agent elsewhere when the precondition fails: search_registry for keywords, discover_capabilities for plain-language needs, list_entries for the whole catalogue. It also warns not to guess a slug.

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