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

Annotations already establish a safe, closed-world read (readOnlyHint=true, openWorldHint=false). The description adds a genuine behavioral trait beyond that: the parameterless mode enumerates the available vocabulary, which an agent cannot derive from the schema or annotations.

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?

Two sentences, no filler, and the core capability is front-loaded before the example parenthetical and the fallback mode. The example lists are dense but every item is load-bearing because they define the breadth of acceptable input.

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 one-optional-parameter lookup with no output schema, the description covers everything needed: what it returns ('a plain-English meaning'), the full vocabulary scope, and the no-argument behavior. Nothing an agent needs in order to call it correctly is missing.

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 baseline would be 3, and the description earns an extra point by characterizing the accepted value space in a way the schema's bare 'The word or tag to explain' does not — acronyms (IBAN, LEI, UETR), site concepts (x402, MCP), and XML tag abbreviations such as GrpHdr or IntrBkSttlmAmt.

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 states a specific resource (plain-English meanings of site vocabulary and ISO 20022 tag abbreviations) and enumerates concrete example terms, so an agent immediately knows what domain this glossary covers. It stops short of differentiating itself from near-neighbors like explain_issue or get_guide, leaving the agent to infer the boundary.

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 gives one useful call-mode rule — 'Without a term, lists the words' — which tells the agent an argument-free invocation is valid and what it returns. It offers no guidance on when to prefer this over explain_issue, get_guide, or get_overview, all of which a confused agent might reasonably reach for first.

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