Balancing context size and callable tool metadata with CAP's MCP adapter

CAP supports the Model Context Protocol, and treats it beautifully as "just another protocol". The support comes in the form of the @cap-js/mcp plugin, which has these feature flags: { "cds": { "mcp": { "per_action_tool": false, "prefix": false, "format": "cql" } } } In this post I want to explore the per_action_tool setting. Sample service To illustrate, let's use the classic capire/bookshop sample project which, amongst other resources, has a service defined in srv/cat-service.cds like this: using { sap.capire.bookshop as my } from '../db/schema'; service CatalogService @(path:'browse') { /** For displaying lists of Books */ @readonly entity ListOfBooks as projection on Books { *, currency.symbol as currency, } excluding { descr }; /** For display in details pages */ @readonly entity Books as projection on my.Books { *, // all fields with the following denormalizations: author.name as author, genre.name as genre, } excluding { createdBy, modifiedBy }; @requires: 'authenticated-user'…