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

With no annotations, the description carries the full burden and does well: it discloses the auth requirement (no key), the scope boundary (no holidays/broker hours), and the FX week definition (Sun 17:00-Fri 17:00 New York). Read-only nature is implied by 'informational only' but not stated as such, and pagination/refresh behavior isn't addressed.

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?

Front-loaded with the two most decision-relevant facts (free, no key), then the session content and limitations in tight successive sentences. Dense but every clause earns its place.

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?

No output schema exists, and the description compensates by enumerating what is returned (open now, active overlaps, next open/close, dual-zone times). Combined with the explicit exclusion of holidays and broker hours, an agent has enough to call and interpret it, though the exact response shape remains unstated.

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 both 'at' and 'tz'. The description reinforces the timezone semantics ('times shown in UTC and any IANA zone', DST-aware), which aligns with the tz param, but adds no syntax or default details beyond what the schema provides. Baseline 3 is appropriate.

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 resource (forex session clock) and enumerates the exact sessions covered (Sydney, Tokyo, London, New York) plus the outputs (open now, overlaps, next open/close). An agent can tell this is an FX session-timing tool without opening the schema.

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?

Gives useful context (free, no key, informational only) and a caveat that holidays and broker hours are excluded, but never states when to prefer this over alternatives such as the sibling market_hours or time_tools. Usage is implied by the content rather than explicitly routed.

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