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

Beyond the readOnlyHint/destructiveHint annotations, it discloses the null-on-no-access return and, importantly, that a wrong-owner id is indistinguishable from a missing one — a non-obvious visibility/authorization behavior an agent could otherwise misread as a data bug. It also flags the conditional enrichment (receipt summary only when receipt_id is set).

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?

One front-loaded sentence carries the purpose, scope, and payoff, followed by two short clarifying clauses. The parenthetical is dense but every element earns its place; only minor tightening is possible.

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 carries the return-value burden and does so — naming the record fields, the conditional receipt summary, and the null case. For a single-parameter read tool this is complete enough to call correctly without further exploration.

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% and the single `id` parameter is typed as integer-or-string, but the description only says 'by id' without clarifying accepted formats or how a string id differs from a numeric one. It confirms the identifier is the warranty's own id (not a receipt or product id), which is modest added value over the bare 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 ('Read a single warranty by id') and enumerates what comes back (is_active, warranty_until, reminder_offsets, linked receipt summary), which cleanly separates it from list_warranty_items and the add/update/delete siblings.

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 'so ONE call answers ...' framing tells the agent when this tool is the right single-shot choice rather than fanning out across calls. It stops short of naming an alternative or an explicit when-not case, so it is clear context rather than full routing guidance.

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