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ppsspp_watch_value

Read-only

Watch a memory address for value changes by polling every N frames without pausing the CPU, recording old/new values and timestamps; a zero-pause alternative for hot-address debugging.

Instructions

PURPOSE: Value-change watch on an address — zero-pause alternative to a read watchpoint.

USAGE: session_id + address + mode + interval. Polls the value every interval_frames and records changes (old/new/frame/time). Pure reads: the CPU is never paused, so hot addresses are safe (storm-free).

BEHAVIOR: READ-ONLY. Polling loop; never mutates state; blocks ~duration_frames/60 seconds (cap 18000 frames).

RETURNS: {address, size, mode, samples, first_value, last_value, changes: [{frame, t_s, old, new}], change_count}.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`mode`	No	Read width for change detection: 'u8', 'u16' or 'u32' (default u32). Must match how the watched value is meant to be read.	u32
`address`	Yes	Address to watch, hex string (e.g. '0x08A0D000').
`session_id`	Yes	Active session ID.
`duration_frames`	No	Total watch window in frames (cap 18000 ~ 5 min at 60fps). A-19: holds the per-session lock for the WHOLE window — concurrent tool calls on this session get SESSION_BUSY after ~5s; use short windows or poll repeatedly instead.
`interval_frames`	No	Poll cadence in frames (60 = 1s wall clock).

Output Schema

TableJSON Schema

Name	Required	Description	Default
`mode`	Yes
`size`	Yes
`address`	Yes
`changes`	Yes
`samples`	Yes
`last_value`	Yes
`first_value`	Yes
`change_count`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv0.1.7Oct 7, 2026

changedInput schema / properties / duration_frames / description

Previous value: -"Total watch window in frames (cap 18000 ~ 5 min at 60fps)."New value: +"Total watch window in frames (cap 18000 ~ 5 min at 60fps). A-19: holds the per-session lock for the WHOLE window — concurrent tool calls on this session get SESSION_BUSY after ~5s; use short windows or poll repeatedly instead."

changedInput schema / properties / mode / description

Previous value: -"Value interpretation for change detection."New value: +"Read width for change detection: 'u8', 'u16' or 'u32' (default u32). Must match how the watched value is meant to be read."

Addedv0.1.6Oct 4, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true, destructiveHint=false, so safety is partly covered, but the description adds genuinely new context: it is a polling loop that never mutates state, it blocks ~duration_frames/60 seconds (cap 18000 frames), and it is 'storm-free' on hot addresses. The concurrency/lock behavior (SESSION_BUSY) is only in the schema, not here, keeping it short of a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Labeled PURPOSE/USAGE/BEHAVIOR/RETURNS sections front-load the key facts with no filler. The RETURNS block duplicates information already carried by the output schema, costing a little economy, but overall it is tight and skimmable.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With full schema coverage, rich annotations and an output schema, the description supplies the extra behavioral context (blocking duration, cap, lock implications implied via the schema) that an agent needs to call it correctly. It is complete for this tool's complexity, though it could have surfaced the session-lock behavior in prose.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all five parameters including mode, interval_frames and the lock caveat on duration_frames are already documented in the schema. The description adds only a light gloss ('Polls the value every interval_frames and records changes'), which is marginal over what structured fields provide, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The opening sentence names a specific verb+resource ('Value-change watch on an address') and immediately positions it against a sibling concept ('zero-pause alternative to a read watchpoint'). An agent can distinguish it from ppsspp_read_memory and ppsspp_breakpoint without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The USAGE line specifies the required inputs and the description names one alternative (read watchpoint) with the condition that selects this tool (zero-pause, storm-free on hot addresses). It lacks explicit when-not guidance against other siblings like ppsspp_breakpoint or ppsspp_state_observer, so it is clear context but not full routing.

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