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

Annotations already declare readOnlyHint=true, openWorldHint=true, destructiveHint=false, so safety is covered. The description adds nothing about how a 'past moment' is expressed, whether historical snapshots are available for all modes or limited retention, or why idempotentHint=false matters when querying a fixed past time. It restates the topic rather than explaining behavior.

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?

A single short sentence with no padding, so nothing is wasted. However, its brevity comes from omitting essentials rather than from tight editing, and the least useful part ('now') is front-loaded while the temporal-query mechanics are absent.

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?

Given an opaque required parameter, no output schema, and a same-named sibling for live data, the description needs to explain both the input shape and the past-vs-now routing. It does neither, so an agent has to guess before calling.

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?

One required parameter named 'input' with an empty schema (0% coverage) and no enum or nesting. With zero structured guidance, the description carries the full burden of explaining what 'input' should contain (a timestamp? an ISO string? a place?), and it says nothing about it. This is the critical failure for this tool.

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 names the resource (Helsinki buses, trams, metro and ferries), which is concrete. But it explicitly covers both 'now, or at a past moment', which fails to distinguish this tool from its sibling cell_sensor_hsl and actually erases the only thing the '_at' suffix signals. An agent cannot tell from the text alone which of the two siblings is the historical one.

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?

No statement of when to use this versus cell_sensor_hsl, no prerequisite or exclusion. The only implicit cue is the phrase 'at a past moment', which is presented as an option this tool shares with its sibling rather than as the condition that selects it.

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