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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, so the safety profile is covered by structured data. The description adds one genuinely useful operational detail — '(cost: 1 credit)' — which is the kind of metering information annotations cannot express. It stops short of describing output format, error behavior for invalid IANA zones, or whether offsets or zone abbreviations are returned.

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 short clauses, front-loaded with the capability and followed by the cost note. Every element earns its place and there is no redundant restatement of the title or schema.

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 three-parameter, no-output-schema tool with full schema coverage, the description is minimally adequate but leaves gaps: it does not clarify that no parameters are marked required in the schema while 'datetime' is described as required, nor does it say what the returned two-zone representation looks like. An agent could still call it correctly, but would be guessing at the response shape and requiredness.

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%, so the schema already documents 'from' and 'to' as IANA zones and 'datetime' as ISO 8601. The description only echoes the ISO datetime concept and the two-zone scope, adding no syntax, default, or format detail beyond the schema. Baseline 3 is appropriate when the schema carries the semantic load.

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 states a specific verb and resource ('Show an ISO datetime in two time zones'), which is materially different from siblings like time_now (current time), fx_rates, and public_holidays. It does not explicitly name or contrast with those siblings, but the purpose is unambiguous from a single sentence.

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: because it takes an existing ISO datetime plus a 'from' and 'to' zone, an agent can infer it is for converting a known timestamp rather than fetching the current time. However, there is no explicit statement about when to prefer this over time_now, nor any exclusion or prerequisite guidance.

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