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

Annotations only assert readOnlyHint=true; the description goes well beyond that by disclosing the provenance payload (source URL, retrieval time, connector version), the verification status and citation envelope, and the revision-aware semantics of asOf ('before any later revision, available from the series' first ingest forward'). That is substantive behavioral context an agent could not infer from the annotation.

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?

Three sentences, front-loaded with purpose then consumption/control semantics, with no filler. Density is high but each clause carries operational information; nothing reads as padding.

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?

With no output schema, the description does the work of describing the return shape (per-value provenance plus a series-level verification/citation envelope) and the temporal parameters. Minor gaps remain around error behavior and the semantics of the required source/seriesId pair, but an agent has enough to call this correctly.

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 67%, and the description compensates meaningfully: it restates the YYYY-MM-DD format for start/end, explains the 60-point default when no window is given, and clarifies what asOf actually returns (store state on that date, ignoring later revisions) plus the availability boundary. It adds interpretation the schema's terse descriptions do not.

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?

Opens with a specific verb+resource framing: 'Observation values for one series.' An agent can immediately tell this returns data points rather than metadata. It does not explicitly name get_series as the metadata sibling, so it stops short of full sibling differentiation, but the scope is unambiguous.

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 concrete operating context: default window of 60 points, use start/end or latest to control the window, and pass asOf for point-in-time reads. It never states when to reach for this rather than get_series or get_series_stats, so no explicit alternative routing, but the usage conditions are clear.

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