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

Goes well beyond the annotations by disclosing the branching side effect (existing favorite is DELETED, otherwise created), the scope limit ('wirkt nur auf das eigene Konto'), and the reversibility (a second identical call undoes the first). This reconciles with destructiveHint=false and idempotentHint=false — the deletion is self-reversible, so no annotation contradiction, and the description supplies the context the annotations lack.

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?

Front-loads the core behavior, then the caveat, then the guidance — a logical order with no wasted sentences. Minor deductions for the bilingual duplication and the trailing keyword tag ('| EN: favorite, bookmark, quick access'), which is padding rather than information.

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 two-parameter mutation with full schema coverage and no output schema, it covers state dependence, scope, reversibility, and alternatives — everything needed to call it safely. It stops short of saying what the return value reports (e.g. the resulting state), which would have made the round-trip behavior fully predictable.

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 description coverage is 100%, so both parameters (url required, title optional with a stated default) are already fully documented. The description only implies that the URL is the identity used for the toggle; it adds no format, normalization, or matching semantics beyond the schema. Baseline 3 applies.

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 pair — toggling the favorite status of an object ('Favoriten-Status eines Objekts umschalten') — and disambiguates from siblings by naming onto_favorite_add and onto_favorite_delete. An agent can distinguish it from the add/delete variants without opening 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 selection rule: use this when you do not know the current state, because no pre-read is needed; use onto_favorite_add to add deliberately or onto_favorite_delete to remove deliberately. Both the use case and the alternatives are spelled out.

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