Investigation Notes Agent Skill
Structured scratch tracking document for investigation state during bug hunts - prevents re-reading code, losing context, and rabbit holes; maintains external memory so you don't re-derive conclusions
Install
one command, takes just this skill from the repositorynpx skills add https://github.com/cloudflare/workerd --skill investigation-notesThe instruction itself
7 sections, as written by the authorInvestigation Notes
Overview
During bug investigations, maintain a lightweight scratch document as external memory. This prevents
re-reading code you've already analyzed, losing track of which hypothesis you're testing, and
silently drifting into rabbit holes.
Core principle: Write it down once, refer to it later. Re-reading your one-line note is faster
than re-reading 200 lines of source.
Always keep the document up to date with your current focus, hypotheses, and learnings from
code reads and tests.
Always refer to the document before re-reading code or forming a new hypothesis. If the
information is there, use it. If it's not sufficient, read the code, then write a better note.
The document never takes priority over writing or running a test. If you're choosing between
updating notes and writing a test, write the test. Update the notes after.
The Document
Create ~/tmp/investigate-<short-name>.md during orientation (step 2 of /investigate).
The short name should be descriptive enough to identify the investigation (e.g.,
investigate-concurrent-write.md, investigate-pipe-zombie-state.md).
Once created, notify the user and provide the file path so they can open it in their editor.
Format
# Investigation: <one-line bug description>
## Error
<assertion/crash message, file:line — written once, never changes>
## Current Focus
<single sentence: what you are doing RIGHT NOW>
## Hypotheses
1. [TESTING] <one sentence> — test: <test name or "not yet written">
2. [REJECTED] <one sentence> — disproved by: <one sentence>
3. [CONFIRMED] <one sentence> — evidence: <test name + result>
## Code Read
- `file:line-range` — <what you learned, short paragraph or bullet>
## Tests
- `file:line` "test name" — <result + what it means, one sentence>
## Ruled Out
- <thing you investigated and eliminated, one sentence why>
## Next
1. <concrete next action>
2. <fallback>
Creation
Create the document when:
- You have more than one hypothesis to track
- You've read more than 3 files/functions
- You're about to re-read code you already read
- The investigation is going to span multiple iterations of test-write-run
When created, populate Error, Current Focus, your current hypotheses, and anything you've
already learned (backfill "Code Read" and "Tests" from what you've done so far).
Rules
- Always update "Current Focus" before starting any new thread of work
- Always Add a hypothesis for what you're doing
- Always update the document after each significant action:
- After reading a function or file section → add to "Code Read"
- After forming or rejecting a hypothesis → update "Hypotheses"
- After running a test → update BEFORE doing anything else. Record: what test ran, what the
result was, what it means for the active hypothesis. This is non-negotiable — it takes 30
seconds and prevents the pattern of running multiple tests, losing track of what they proved,
and falling back to code reading.
- After starting a new thread of work → update "Current Focus"
- Do not dump large amounts of code into the document. Instead, reference it by
file:line. - Do not reorganize or reformat the document - this is a scratchpad, not a report.
- You may include brief, simple diagrams if they help you understand and retain information.
Hypothesis Limits
- Maximum 3 active hypotheses at a time. If you want to add a fourth, reject or merge one first.
- Maximum 1
[TESTING]at a time. Commit to one, test it, resolve it, then move on. - Every hypothesis must have a test or a concrete plan to write one. "Need to investigate
further" is not a valid state — that's analysis paralysis wearing a label.
Valid statuses:
[UNTESTED]— formed but not yet tested. Must become[TESTING]or[REJECTED]soon.[TESTING]— actively being tested. Only one at a time.[CONFIRMED]— test reproduced the bug as predicted.[REJECTED]— test disproved it, or evidence rules it out. Include why.[SUPERSEDED]— replaced by a more specific hypothesis. Reference the replacement.
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How to use it
Take cloudflare/investigation-notes from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.