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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered; the description nonetheless adds meaningful behavior beyond them — the result is a source-selected window rather than a full archive, dates are passed through as unmodified source strings, and optional fields preserve source presence and types. Those are exactly the fidelity caveats an agent must know before consuming the data. It does not discuss volume or paging, which is a minor omission for a collection-returning call.

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 scope constraint is front-loaded and every clause about archive scope and string dates earns its place. However, the long enumeration of return fields (source ID, title, detail URL, dates, joined count, hue, voting-end, featured, highlight) duplicates an output schema that already exists, and the second sentence is a dense run-on. Trimming the field list would make the definition tighter without losing anything the agent cannot get from structured data.

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 zero-parameter read tool with an output schema and readOnly/openWorld annotations, the description supplies everything the remaining burden requires: scope boundaries, data-fidelity caveats and an explicit statement that no filtering inputs exist. An agent can call this correctly without consulting anything else.

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?

With zero parameters the baseline is 4, and the description goes further by explaining why the schema is empty: the site's filter controls are local, so no server-side equivalents exist. That pre-empts an agent trying to pass filters. Nothing more is needed on the parameter dimension.

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 opens with a concrete verb and resource ("Get the complete jam collection ... from itch.io's public calendar") and enumerates what each entry carries, so the tool's scope is unmistakable. It also rules out the most likely confusion by stating the result is a source-selected window rather than a historical archive. It falls short of a 5 only because it never names the filtering/browsing siblings an agent should use instead.

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?

It clearly frames the calling context: read the calendar as-is, expect a bounded window, and do not look for server-side filtering because participant-count, duration and featured are local site controls. That is genuine when-to-use guidance with an implied exclusion. It stops short of naming an alternative tool for filtered or historical needs, leaving that routing to inference.

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