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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), and the description adds genuinely operational detail not present in structured fields: an 8 s timeout, 5-redirect cap, 768 KiB payload ceiling, and 100-item ceiling. The 'does not fetch linked articles' line also scopes behavior in a way the annotations cannot express.

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 tight sentences: capability and formats first, usage and exclusion second, hard limits last. No sentence is redundant and the most decision-relevant information is front-loaded.

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?

An output schema exists, so return structure need not be explained; the description covers formats, operational limits, and the key non-behavior (no article fetching). It does not mention failure behavior for malformed or unreachable feeds, which is the one gap for a network-fetching tool.

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 50%: url is documented, max_items is not. The description's '100 items' limit indirectly explains max_items' upper bound and purpose, but it does not state the default of 50 or how items beyond the cap are handled. Marginal compensation for the coverage gap, so baseline 3.

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 ('Fetches and normalizes') plus the exact format scope (RSS 2.0, Atom 1.0, JSON Feed) and the output shape ('stable item list'). That format scope cleanly separates it from siblings like parse_sitemap, extract_links, and fetch_markdown without the agent needing to open 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?

Gives an explicit when-to-use condition ('consuming update feeds without format-specific parsing') and one clear exclusion ('does not fetch linked articles'), which steers the agent toward fetch_markdown/extract_links for article bodies. It stops short of naming a sibling alternative explicitly, so it is clear context rather than full routing guidance.

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