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

Annotations already declare destructiveHint=true, readOnlyHint=false, idempotentHint=false and openWorldHint=false, so safety is covered; the description goes further by explaining that operations apply in order, that activity indices are 1-based positions evaluated against the agenda as it stands after earlier operations, that start/end times are recomputed automatically, that added activities receive full step-by-step method details, and that the full branded brief is returned and rendered in chat. That is substantive behavioral context beyond the structured fields.

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 critical scoping ('IN PLACE', 'existing session') and the one-call rule are front-loaded, and the operational semantics come next. The trailing sentences about returning the branded brief and editing the same session Metodic Studio shows partly restate the earlier Metodic reference, so it is slightly longer than it needs to be.

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?

There is no output schema, and the description compensates by stating exactly what comes back (the updated, branded session brief in full, rendered in the chat). Combined with the ordering semantics, automatic time recomputation, and the one-call constraint, an agent has everything needed to invoke this correctly against a 2-parameter, fully documented schema.

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 the operation shapes and field meanings, giving a baseline of 3. The description adds genuine meaning beyond that by explaining the ordering semantics of the operations array and the fact that indices are resolved against the mutated agenda state, which is the subtlest part of the contract.

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 and resource ('Modify an existing session's agenda IN PLACE') and enumerates the concrete change types (retime, rename, move, remove, update, add), which maps directly onto the operation enum. It clearly separates this from design-time creation by scoping it to an 'existing' session, so an agent can distinguish it from siblings like design_session and get_session.

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 gives an explicit when-to-use ('Modify an existing session's agenda'), an explicit when-not/anti-pattern ('Put EVERY change the user asked for in ONE call — a second call paints a second full session brief'), and an alternative to avoid ('Prefer this over sending the user to Metodic for an edit'). The batching instruction in particular is the kind of guidance that prevents a real agent failure mode.

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