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

Annotations already declare readOnlyHint, idempotentHint and non-destructive behavior. The description adds genuinely non-derived behavioral context: unknown fields are not inferred as free/unlimited, only known enrollment conditions are reported, and signal quality is out of scope. That epistemic-disclosure rule is exactly what an agent needs to interpret partial results, though return formatting/pagination is not discussed.

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 comparison verb and scope front-loaded; each clause carries information (compared fields, no inference of unknowns, no signal-quality comparison). Slightly dense for a single run-on sentence but no wasted text.

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 read-only, single-parameter tool with no output schema, the description covers what is compared, what is deliberately excluded, and how unknown values are handled. The only real gap is that it never routes the agent from get_plan/search_plans into this tool.

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 a single parameter at 100% schema coverage, the schema already documents the slug array, its 2–3 count bounds and its provenance from search_plans. The description only adds the qualifiers '不同' (distinct) and '在售' (on-sale), which is marginal added meaning — the baseline 3.

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 (对比两到三款在售套餐) and enumerates the compared dimensions (月租、通用及定向流量、通话、已知办理条件), which is far more than a restatement of the name. It implicitly separates itself from get_plan/search_plans via the 2–3 slug operand, but never names those siblings explicitly, so it falls short of a 5.

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?

Usage is implied by the 2–3 slug constraint and the source of slugs (search_plans per the schema), and '不比较信号质量' functions as a scope exclusion. However, there is no explicit statement of when to prefer compare_plans over calling get_plan repeatedly, nor any prerequisite guidance.

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