history

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

readOnlyHint=true already covers safety, and the description adds genuine behavioral context beyond it: default result ordering (oldest first), that limit retains the *latest* entries and that limit=0 returns everything, and the null-vs-absent semantics of the replaced value. What is missing is any note on pagination or the result shape, which would matter given no output schema.

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?

The text is short and every clause carries information, but it is a semicolon-chained run-on with no lead verb and heavy domain jargon ('Keel', 'watermark', 'tenant then'), so it is not front-loaded and requires re-reading. Density here buys brevity at the cost of parseability.

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 10-parameter, zero-coverage, no-output-schema tool, the description covers most of the tricky temporal semantics, which is more than most. It still leaves two parameters (task, scope) undocumented and misstates the detail enum, and it never says what a returned record looks like, which the agent needs since no output schema exists.

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 0%, so the description must carry all ten parameters, and it explains subject, since, until, predicate, as_known_at, changed_since, limit and detail. It leaves 'task' and 'scope' (agent/task/tenant/global) entirely unexplained, and its 'detail: concise or full' contradicts the three-value enum that also allows 'text'; 'was' is described but is not actually an input parameter, which is confusing.

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 opening clause 'Facts over time of a subject, oldest first' describes the resource and the ordering, but never supplies a verb – the agent must infer that this is a read/query operation. It partially differentiates scope ('no subject + since/until: every change in the tenant') but none of the sibling tools (context, search, related) are named or contrasted.

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 conditional guidance for one branch – omitting subject while supplying since/until yields a tenant-wide change feed. However there is no explicit when-to-use-this vs. search/context, no statement of prerequisites or cost, and the relationship between as_known_at and changed_since is only hinted at, leaving the agent to infer which one applies.

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