aider session format

Store and files

aider appends Markdown to .aider.chat.history.md in its launch directory. The default home file is ~/.aider.chat.history.md; AIDER_CHAT_HISTORY_FILE relocates it. deja also scans each directory in the platform path-list variable DEJA_AIDER_ROOTS, to two levels below each root.

One history file contains multiple sessions. A session begins with:

# aider chat started at 2026-07-17 09:00:00

#### Show me the failing query

The query misses the tenant predicate.

> Applied edit to query.go

Message mapping

Outside fenced code blocks, #### starts or continues a user message. Plain Markdown is assistant output. Lines beginning with > are tool or system output and are not indexed. Blank lines remain part of the current message.

The header timestamp uses local time with layout YYYY-MM-DD HH:MM:SS. aider does not store message timestamps, so every message receives the session start. It does not store a session ID; deja derives a stable ID from the history path and the session's ordinal in that file.

Skills

None, and there is nothing to build on. aider loads instruction files rather

than offering a catalogue an agent picks from: --read (and a CONVENTIONS.md by

habit) puts a file in every message, which is exactly what deja's context file

already is. A skill here would be the same always-on text under another name.

Known quirks and drift

The file is append-only and can contain many launches.
Markdown fences may contain lines beginning with #### or >; these are content, not role markers. The parser tracks triple-backtick fences.
<blank> after the user prefix represents an empty line.
Tool output terminates an assistant block but does not become a message.
Moving a history file changes deja's derived session IDs because the path is part of the ID.

Last verified: 2026-07-27

deja reads this format and nineteen others, and turns what it finds into memory your agents can search. See the harness matrix for what is wired where, or install it and search your own history.