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

The description discloses behavioral traits beyond the annotations: it states that oversized images are resized rather than rejected, that entfernen removes the image, and that the current state is not visible in session_lesen. These details are not in the annotations (readOnlyHint=false, destructiveHint=false, idempotentHint=true) and significantly help the agent anticipate behavior. No contradictions found.

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 moderately long but every sentence contributes. It is well-structured: purpose first, then rationale, then parameters, then removal, then a caveat. It is front-loaded with the core action and not excessively verbose given the tool's complexity. Slightly longer than necessary, but justifiably so.

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 tool with 4 parameters, no output schema, and full schema coverage, the description covers all essential aspects: image format, resizing behavior, mode semantics, removal option, and the critical caveat about not being able to read the current image from session_lesen. An agent has everything needed to invoke it correctly.

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 baseline is 3. The description adds practical value by explaining that 'bild' accepts both data-URI prefixed and raw Base64, by giving concrete examples for 'modus' (fit vs crop), and by clarifying the auto heuristic (width >1.5:1 treated as logo). This goes beyond the schema's own descriptions, earning a 4.

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 clear verb and resource: 'Setzt das Bild, das auf der Kachel und in der Liste vor der Session steht' – it sets the title image for a session tile. It distinguishes itself from siblings like session_aendern (which edits session fields) and session_lesen (which reads), making the purpose unmistakable.

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 provides explicit guidance on when to use the tool (to set a logo or photo) and when not to rely on it (the current image is not in session_lesen, so the agent must ask the user). It also explains mode selection (fit for logos, crop for photos, auto heuristic) and removal via entfernen, covering the main usage decisions.

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