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

The description goes beyond the readOnly/idempotent/openWorld annotations by disclosing a concrete quota and cost model (10 free calls/day, then $0.001 via HTTP endpoint or X-API-Key credits), which is genuinely useful operational context. However, it doesn't say what an agent sees when the free quota is exhausted (error vs. charge prompt) or whether unit strings are case-sensitive, so it stops short of a 4.

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: capability scope first, then pricing/access. Every clause carries information (unit domains, the KB/KiB and ping edge cases, the quota). Nothing is redundant with the title or annotations.

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 an output schema present, return values need no explanation, and the description covers scope plus the cost/rate dimension that annotations omit. The remaining gap is edge-case behavior: invalid or ambiguous unit strings, and what happens at the quota boundary — minor for a simple stateless converter.

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 coverage is 100% and the schema itself only labels the three fields as 'unit'/'unit'/'number', so the description's specific callouts — KB vs KiB distinction, 坪/ping support, exact wei/gwei/ETH — add real meaning about what unit identifiers are accepted. It still doesn't spell out accepted spellings, aliases, or case rules for `from`/`to`, keeping it below a 5.

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 enumerates the conversion domains covered (length, mass, volume, area incl. 坪/ping, speed, time, data, energy, pressure, temperature, wei/gwei/ETH), which tells an agent precisely what class of request this tool handles. It falls short of a 5 because it never distinguishes itself from overlapping siblings like currency_convert, time_convert, or number_base — an agent could plausibly route a duration or number-base request to either tool.

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 when-to-use / when-not-to-use guidance and no mention of alternatives, despite several siblings that overlap on time and numeric conversion. The only selection-relevant signal is implicit: the category list hints that currency and base-N conversion are out of scope, but the agent must infer that.

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