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

With no annotations, the description carries the full burden and does disclose a genuinely non-obvious behavior: it refuses to compare and returns comparable:false with a reason when a service publishes no monthly subscription. That is a valuable edge-case disclosure, though it says nothing about error handling for unknown or ambiguous service identifiers.

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?

Two tight sentences with the primary behavior front-loaded and the failure mode immediately after. No filler.

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?

Partial coverage: the failure mode and a return field (comparable:false) are noted, but with no output schema and no annotation support the description leaves the a/b identifier format, matching rules (exact vs fuzzy), and error cases unexplained.

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 both parameters are opaque single letters (a, b). The description only says 'two services' and never clarifies that a and b are service identifiers, nor whether they are IDs, slugs, or names. It fails to compensate for the empty 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 (compare) and resource (two services) scoped to the cheapest published monthly price, which clearly separates it from siblings like get_service_prices or get_cheapest_by_category. It stops short of explicitly naming an alternative, so it is clear but not sibling-differentiating.

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 comparison scope implies when to reach for this tool (pairwise comparison of exactly two services), but there is no explicit when-not guidance or named alternative against get_service_prices/get_cheapest_by_category. Usage must be inferred from the stated purpose.

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