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

The description adds a genuinely non-obvious side effect: setting `level` or `target_level` resets `goal_set_at` and zeroes the pace estimate. That goes well beyond the annotations. It still doesn't explain why destructiveHint=true beyond that reset, nor whether omitted fields are preserved (merge vs replace) or how the patched values are validated.

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?

Two dense sentences, front-loaded with the action and followed by the important side effect. The parenthetical field list is long but each item maps to a patch key, so it earns its space.

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?

No output schema exists, yet the description tells the agent exactly what is returned (the profile plus its field list) and discloses the one destructive consequence. Only patch merge semantics and validation rules are missing, which is a modest gap for a mutation tool.

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 0% and `patch` is a free-form object with additionalProperties, so the description carries the burden — and it does, enumerating all eleven patch keys (level, purpose, about, mode, goals, deadline, target_level, advance, new_per_day, speed_ru, speed_lang). It also defers value formats to profile(), which is a practical pointer. Types and allowed values (e.g. for `mode` or level scale) remain undocumented, so not a 5.

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 ('Change fields of the learner's profile in the active language') and names the field set that can be changed. The verb 'change' plus the return value implicitly separates it from the read-only sibling `profile`, but that contrast is never made explicit.

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?

Usage is only implied: a reader infers you should call `profile` first to learn the field formats and call this only when mutating. There is no explicit when-to-use / when-not statement and no prerequisites (e.g. must a profile exist, must a language be active).

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