timeline

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

With no annotations, the description carries the full behavioral burden. It usefully discloses that results include superseded values and carry validity windows — meaningful output-shape context an agent would not otherwise know. It does not state that this is a read-only operation, how results are ordered or paginated, or what happens when the subject has no recorded history.

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 sentences, front-loaded with what the tool returns and followed by the question it answers. No filler and nothing repeated from the 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 single-parameter read tool with no output schema, the description covers the return concept (historical values with validity windows) reasonably well. The gaps are the undefined 'subject' parameter and unstated behavior for empty or unknown subjects, which matter for correct invocation.

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?

There is one parameter with 0% schema description coverage, so the description must compensate and does not. 'Subject' is never defined — whether it is an entity identifier, a name, or a key, and whether it must match a previously recorded subject — leaving the only input ambiguous.

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 gives a specific verb-like retrieval semantics: 'Every value ever recorded for a subject, with validity windows — including superseded ones.' It clearly contrasts with a current-state lookup by emphasizing 'every value ever' and 'superseded,' so an agent can distinguish it from snapshot-style siblings like current_fact without opening the schema. It stops short of naming a sibling explicitly, which keeps it from 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?

'Use it to answer what changed and when?' is a genuine usage cue that implies when this tool beats a current-value lookup. However, there is no explicit when-not guidance, no named alternative, and no prerequisites or failure conditions stated.

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