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

Annotations already indicate this is a mutating operation (readOnlyHint=false, destructiveHint=false). The description adds valuable behavioral context: modules are appended to a day, subsequent content shifts automatically, parallel groups receive the same 'parallel' label, and only durations in minutes are used (no times). It doesn't fully describe all side effects (e.g., what happens to existing modules after insertion), but it goes well beyond the 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?

The description is compact and front-loaded with the core action and the most important constraint (own sessions only). The parallel-group explanation is somewhat long but necessary for correct usage. Every sentence earns its place, though the parallel explanation could be slightly trimmed without losing meaning.

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 mutating tool with no output schema, the description covers the key behavioral aspects: ownership prerequisite, time handling, parallel groups, and insertion position. It doesn't explicitly state what the response looks like or whether the operation is reversible, but the schema and annotations cover the parameter space well. The main gap is lack of return-value info, which is minor for an append operation.

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 the schema already documents all parameters thoroughly. The description adds important semantic guidance: 'nur Dauer in Minuten, keine Uhrzeiten' clarifies the minuten parameter, and the parallel field explanation is extensive. It also clarifies that 'nach_nummer' is optional and defaults to end of day. This is above the baseline 3 because the description adds meaningful usage context beyond the schema.

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 verb ('Hängt ... an') and resource ('Module an einen Tag einer bestehenden Session'), and clearly distinguishes from siblings by naming session_kopieren for foreign sessions and anhang_hinzufuegen for file attachments. It also clarifies the operation is for appending modules, not modifying or moving them.

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 when to use this tool (own sessions) and when not (foreign sessions → session_kopieren first). It also gives a clear alternative for whole files (anhang_hinzufuegen) and explains the parallel-group usage rule. This is strong routing guidance.

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