Adds or removes an injected style tag by ID in the League client document head, with optional persistence across reloads; styles do not enter shadow roots.
Adds (or with remove=true removes) a in the document head under an id. Note: styles do not reach inside shadow roots; target hosts or use ::part where available.
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | ||
| css | No | ||
| remove | No | ||
| persist | No | Re-apply after reloads while this server runs. |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only declare readOnlyHint=false, so the description carries most of the burden and does it well: it discloses where the style lands (document head), that styles are keyed by id, and the significant shadow-DOM limitation with a suggested workaround. It doesn't say what happens when a style with the same id already exists, which is the main remaining behavioral gap.
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 sentences, front-loaded with the core action and its inverse, followed by a clearly flagged caveat. Nothing is wasted and the limitation note earns its place.
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?
With no output schema and only a readOnlyHint of false, the description covers placement, idempotency-by-id, and the shadow-root caveat, which is enough to call it correctly. Minor gaps remain on overwrite semantics and the persist parameter, but the schema covers persist.
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 only 25% (just persist), so the description must compensate. It explains the id keying and the remove=true toggle, effectively documenting two of four parameters, but leaves css and the interaction of persist with reloads to 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 uses a concrete verb and resource ('Adds ... a <style> in the document head under an id') plus the removal variant, so an agent immediately knows what the tool does. It is distinguishable from siblings like script or eval, though it never names them explicitly.
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 implied rather than stated: 'Adds (or with remove=true removes)' shows the two modes, and the shadow-root note tells the agent when this tool won't work. There is no explicit when-to-use-vs-alternatives guidance for injecting styles versus using script/eval.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.