Progressive Disclosure for AI Agents

Use <?catalog?> with a per-file summary front matter field to emit a one-line index of a directory, so AI coding agents read a few thousand tokens of metadata up front and only Read the files a task actually touches.

AI coding agents (Claude Code, Codex, Copilot, Cursor) pay context tokens for every file they pull into the prompt. Loading every doc in a repository eagerly is the easy default and the wrong one: 60 docs at 2 000 tokens each is 120 000 tokens spent before the agent has done anything.

Progressive disclosure inverts that. The agent file (CLAUDE.md, AGENTS.md, .github/copilot-instructions.md) carries a short index — one line per doc, naming the specific data each doc contains — and the agent Reads the full file only when a task makes one relevant.

mdsmith builds that index for you. This guide is the recipe.

# Motivation

A three-tier loading model is the broader pattern:

1. Metadata. Filenames + one-line summary strings. Cheap; always in the prompt.
2. Instructions. A skill or guide body the agent pulls in when the metadata says it applies.
3. Reference. Full source files the agent reads on demand once it knows what it is looking for.

Tier 1 is the bottleneck. A vague index (“docs page about catalog”) forces the agent to load tier 2 to decide whether tier 2 was needed at all — the disclosure stops being progressive. A precise index (“How <?catalog?> projects a summary field into a generated bullet list, with the where and sort parameters”) lets the agent skip the file without opening it.

mdsmith’s <?catalog?> directive automates tier 1. Each tracked file declares a summary in YAML front matter; the directive generates the index from those summaries; mdsmith check flags drift; mdsmith fix re-renders.

# How mdsmith does it

CLAUDE.md is the live example. A single <?catalog?> under its ## Docs heading matches every tracked doc under docs/** — four ! patterns exclude research notes, security reports, brand copy, and proto.md templates — sorts by path, and emits one bullet per match:

<?catalog
glob:
  - "docs/**/*.md"
  - "!docs/research/**"
  - "!docs/security/**"
  - "!docs/brand/**"
  - "!**/proto.md"
sort: path
header: ""
row: "- [{summary}]({filename})"
?>
- [How generated sections work — markers, directives, and fix behavior.](docs/background/concepts/generated-section.md)
- [Build commands, project layout, code style, test fixtures, coverage gate, and merge conflicts.](docs/development/index.md)
...
<?/catalog?>

The ~110-doc tree compresses to ~3 400 tokens of index. The agent reads CLAUDE.md once at session start and already knows which file to open for any task it gets.

AGENTS.md is a thin shim that <?include?>s CLAUDE.md, so Codex and Copilot consume the same index from the same source.

# Step-by-step

# 1. Add a summary to every file in the indexed tree

Front matter on each doc:

---
title: Coverage Gate
summary: >-
  Codecov coverage gate and CI status checks.
---

The summary is what shows up in the agent’s index. Write it like a tier-1 cue: state the specific data the file contains, in one sentence the agent can match against a task description. Vague verbs (“describes”, “handles”, “covers”) force a tier-2 load to confirm.

# 2. Place a <?catalog?> in the agent file

In CLAUDE.md (or AGENTS.md, or any orient-the- agent doc):

## Docs

<?catalog
glob: "docs/**/*.md"
sort: path
row: "- [{summary}]({filename})"
?>
<?/catalog?>

row is the line shape; {summary} and {filename} are pulled from the matched file’s front matter. Without header or footer, the body is just the rows.

# 3. Run mdsmith fix to populate the body

mdsmith fix CLAUDE.md

The empty body between the markers fills in. From this point, the index is read-only: edit the underlying file’s summary (not the body line) and re-run fix.

# 4. Lock in freshness with mdsmith check

mdsmith check .

If anyone edits a file’s summary and forgets to re-render, check fails with an MDS019 diagnostic naming the catalog whose body drifted. Run this in CI; the index cannot rot.

# 5. (Optional) Filter and partition

A single 60-line index is fine for a small repo. For larger trees, partition by category so each section is short enough for the agent to skim:

### Background

<?catalog
glob: "docs/background/**/*.md"
sort: path
row: "- [{summary}]({filename})"
?>
<?/catalog?>

### Reference

<?catalog
glob: "docs/reference/**/*.md"
sort: path
row: "- [{summary}]({filename})"
?>
<?/catalog?>

Or filter by front matter with where:

<?catalog
glob: "plan/*.md"
where: 'status: "🔳"'
sort: numeric:id
row: "- [{id}: {summary}]({filename})"
?>
<?/catalog?>

where is a CUE expression evaluated against the matched file’s parsed front matter. The same grammar mdsmith list query uses drops in unchanged. See Generating Content with Directives for the full parameter reference.

# Common issues

# A file is missing summary

{summary} resolves to an empty string and the row becomes - [](path/to/file.md). Fix with a schema that requires the field. Declare a kind for the indexed tree, point a required-structure schema at it, and list summary as required front matter:

---
title: nonEmpty
summary: nonEmpty
---
# ?

See Schemas for the kind + proto.md wiring. Once the schema is in place, mdsmith check blocks any file in the tree that ships without a usable summary.

# Summaries are too vague to disclose anything

If a summary reads “Docs page about catalogs”, an agent has no way to skip it without loading the file. The repo writing guideline applies: name the inputs (front matter fields, glob patterns, heading levels) and the condition checked against them, not the mechanism. “How <?catalog?> projects a summary field into a bullet list, with where and sort parameters” is a tier-1 cue; “Catalog directive guide” is not.

This is a content rule, not a lint rule. MDS024 paragraph-structure and the surrounding readability rules catch the worst offenders in body prose; summaries are short enough that review is the gate.

# The index is too large to load eagerly

A 200-line catalog still beats loading 200 files, but it crowds out room for the agent’s actual work. Two tactics:

• Partition. One catalog per top-level directory, each under its own heading. The agent reads the index, jumps to the section that matches the task.
• Filter. Pin the catalog to active work with where: 'status: "🔳"' (or kind, or a tag field). Archived material drops out of the index without leaving the repo.

The token-budget rule on CLAUDE.md is the canary: if the index pushes the file over budget, the rule fires before the agent runs out of context.

# A summary disagrees with the file’s content

mdsmith check does not validate summary against the body — it only validates the catalog body against the front matter. Drift here is a content problem, not a lint problem. Two mitigations:

• Keep summary short. A two-sentence summary is hard to falsify; a paragraph is not.
• Treat summary as part of the same change as the content. The review process catches mismatches the same way it catches stale docstrings.

# The field you want to project is a list

row placeholders project scalar values only. A front matter field that is a list or a map renders as an empty string — there is no list-comprehension or join syntax in the placeholder grammar.

For now, project a scalar derived from the list (a joined comma-separated field maintained alongside the structured one), or generate the catalog body from a Go helper that walks the structured field itself.

# Generated index conflicts on merge

Two branches both ran mdsmith fix and both committed the regenerated catalog body — git reports a conflict inside the <?catalog?> markers. Install the merge driver once per clone:

mdsmith merge-driver install

The driver re-runs fix and re-stages the result, so generated-section conflicts resolve without manual intervention.

# See also

• Generating Content with Directives — full reference for <?catalog?> and <?include?>.
• Generated sections concept — markers, directives, and fix behavior.
• Schemas — require a summary field per directory.
• mdsmith list query — same CUE grammar where: uses.