ppsspp-dfx

Overview Schema Source Related Servers Discussions Admin

ppsspp_write_register

Destructive

Write a new value to any CPU register (GPR, FPU, VFPU, PC, HI, LO) in an active PPSSPP debug session. Specify the MIPS register name and hex value; the emulator pauses and resumes automatically.

Instructions

PURPOSE: Set a CPU register (GPR/FPU/VFPU names, plus pc/hi/lo).

USAGE: session_id + name (MIPS ABI names only — 'r5' normalizes to 'v1') + value (hex).

BEHAVIOR: DESTRUCTIVE. Pauses and resumes the CPU automatically (REQUIRED_STEPPING handled internally) — no manual pause needed.

RETURNS: {name, value, response, text}.

Input Schema

TableJSON Schema

Name	Required	Description
`name`	Yes	CPU register name (MIPS standard names). GPRs: 'v0'/'v1'/'a0'-'a3'/'t0'-'t9'/'s0'-'s7'/'gp'/'sp'/'fp'/'ra'/'hi'/'lo'/'pc'. FPU: 'f0'-'f31'. VFPU: 'v0'-'v127'. Numeric aliases like 'r5' are NOT accepted by PPSSPP — use the MIPS standard name (e.g., 'a1' instead of 'r5'). Case-sensitive (lowercase by convention).
`value`	Yes	Value to write, as a hex string (e.g. '0x00000001'). Treated as an unsigned 32-bit int; values outside [0, 0xFFFFFFFF] are wrapped by PPSSPP.
`session_id`	Yes	Active session ID.

Output Schema

TableJSON Schema

Name	Required	Description
`name`	Yes	Register name (e.g., 'v0', 'a0', 'pc', 'hi', 'lo').
`text`	Yes	Unified text representation: 'Wrote 0x{VAL:X} → {REG}'.
`value`	Yes	Value written, hex string (e.g. '0x00000001').
`response`	Yes	Raw PPSSPP WebSocket response (may be empty).

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 16, 2026

TDQS

A4.2/5.0

Behavior4/5

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

The description explicitly discloses that the tool is DESTRUCTIVE, which aligns with the destructiveHint annotation. It also adds valuable behavioral context beyond the annotations: it pauses and resumes the CPU automatically, and handles REQUIRED_STEPPING internally. This is exactly the kind of behavioral detail an agent needs to know before invoking a mutating tool.

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

Conciseness5/5

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

The description is compact and front-loaded: PURPOSE, USAGE, BEHAVIOR, RETURNS. Every section earns its place, and the most important information (destructive, auto-pause) is prominent. No filler or redundancy.

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?

The description covers purpose, usage, behavior, and return value shape. The output schema exists, so return values are already documented. The only minor gap is that it doesn't explicitly state what happens on invalid register names or out-of-range values, but the schema already covers value wrapping. Overall, it's complete for a tool of this complexity.

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 the schema already documents all three parameters thoroughly. The description adds a bit of context (e.g., 'r5' normalizes to 'v1', value is hex) but mostly restates what the schema already says. Baseline 3 is appropriate because the schema does the heavy lifting.

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 description states a specific verb ('Set') and resource ('CPU register'), and enumerates the exact register families (GPR/FPU/VFPU, plus pc/hi/lo). This clearly distinguishes it from sibling tools like ppsspp_write_memory, which writes to memory rather than registers.

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 description gives explicit usage context: it requires session_id, name, and value, and notes that MIPS ABI names are required (with 'r5' normalizing to 'v1'). It also states that no manual pause is needed because stepping is handled internally. It doesn't explicitly name alternatives or when-not-to-use, but the context is clear enough for an agent to select it appropriately.

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