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

Annotations already establish readOnly/idempotent/non-destructive, and the description adds substantial context beyond them: publication cadence (12:00 UTC, frozen window ~24h, never updated later), cost profile (free, no quota, no x402), failure behavior (404 {error:no_issue}), and no paging. This is exactly the behavioral detail structured fields cannot carry.

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?

Purpose and sibling routing are front-loaded, then availability semantics, then return shape — a logical order. It is dense and long, and the 404/no_issue statement repeats the schema description nearly verbatim, which is the only real redundancy.

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?

No output schema exists, and the description compensates by naming every top-level return field and the sub-fields of data, plus the markdown truncation caps (30/30/20) versus the full data window. Combined with cadence and error semantics, an agent has everything needed to call and interpret it.

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 100% (pattern, example, description), so the baseline is 3; the description goes further by stating the omit-for-latest default, the 404 error payload for an unstored date, and the one-issue-per-date/no-paging constraint. It stops short of adding anything about date range bounds or timezone interpretation beyond the 12:00 UTC note.

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?

States a specific verb and resource ('Read one published daily breaking-changes digest') and enumerates the content domain (status flips, deprecations, pricing edits, breaking MCP changes). It also names the three sibling tools it is not, so an agent can disambiguate without opening any schema.

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?

Explicitly scopes the use case ('once-a-day catch-up') and routes the agent to alternatives by condition: list_recent_api_changes for a filtered on-demand feed with no MCP section, check_api_status for live up/down, check_model_deprecation for a single model id. When-to-use and when-not-to-use are both covered.

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