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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and a closed-world scope, so the safety profile is fully covered. The description adds useful context that this is a side-effect-free rating service consumed by the reader, but it says nothing about latency, determinism, or what the returned ratings look like — and there is no output schema to fall back on.

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?

One short sentence with no filler, and the purpose is front-loaded. The passive 'Used by the EyeStill reader view' framing is slightly indirect for a definition an agent must act on, keeping it short of a 5.

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 single-parameter, annotation-covered tool this is close to adequate, but with no output schema the description should say what comes back (per-sentence difficulty ratings? a score range?). It implies a difficulty rating without specifying the shape, leaving the agent to guess at the return value.

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% with a single required array documented as 'Sentences in reading order', so the parameter meaning is already carried by the schema. The description adds only the notion that sentences are 'upcoming' and are rated for difficulty, which is marginal beyond what the schema states.

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 names a concrete operation — rating how hard upcoming sentences are — and its downstream consumer (the EyeStill reader view's pacing). It is clearer than a tautology, but it never distinguishes itself from siblings eyestill_fetch_text and read_with_eyestill, so an agent must infer the split between fetching text and rating it.

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 only says the reader view uses it to slow down on hard sentences; there is no when-to-use rule, no exclusion, and no mention of the sibling tools that supply or consume text. An agent learns the internal caller but not the condition under which it should invoke this tool itself.

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