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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile needs no restating. The description adds useful behavioral context beyond the annotations: tolerance for marks with or without the 'UN' prefix, acceptance of bare codes like 3H1, and the ADR 2025 basis for the compatibility check.

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?

Opens with the core action and what it decodes, then layers the optional compatibility check and the input-source caveat. Dense and front-loaded, though the parenthetical list of mark variants is slightly long relative to the rest.

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 compensates by enumerating the components returned for a decoded mark, so an agent knows what to expect. It is silent on failure behavior for an unparseable mark, which is the only notable gap for this two-parameter 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 100%, so both parameters are already documented, making 3 the baseline. The description still adds meaning: it clarifies that 'mark' can arrive with or without the UN prefix or as a bare packaging code such as 3H1, and frames 'un' as a compatibility check rather than a lookup key.

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 (read/decode) and resource (UN packaging mark), then enumerates exactly what gets parsed: packaging code, performance level, density/mass, test pressure, year, state, maker, plus IBC/large packaging/salvage/reconditioned variants. This is far more specific than the sibling names imply and lets an agent tell it apart from un_number_packaging or ibc_inspection_dates.

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 says how to use the optional UN number ('add a UN number to check whether the container may carry that substance under ADR 2025') and gives a genuine when-not rule: if the user hasn't read the mark off the container, ask for it rather than passing a container description. It does not name sibling tools as alternatives, which keeps it short of a 5.

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