Nostr Filter Designer

Overview

Construct correct REQ filters for Nostr relay queries. The filter syntax has subtle semantics around AND/OR combination, tag matching, and multi-filter subscriptions that agents consistently get wrong without explicit guidance.

When to use

• The task is to build Nostr REQ filters for querying relay data.
• The user needs exact filter semantics for AND/OR behavior, tag constraints, time windows, or multi-filter subscriptions.
• The problem is retrieving the right events—threads, zaps, feeds, replies, reactions—not publishing them.
• The output should be one or more valid filter objects or REQ messages.

Do NOT use when:

• The task is constructing publishable events.
• The work is relay-side implementation of filter matching rather than client-side filter design.
• The request is protocol auth, counting, or another NIP unrelated to REQ filter construction.

Response format

Always structure the final response with these top-level sections, in this order:

1. Summary — state the task, scope, and main conclusion in 1-3 sentences.
2. Decision / Approach — state the key classification, assumptions, or chosen path.
3. Artifacts — provide the primary deliverable(s) for this skill. Use clear subheadings for multiple files, commands, JSON payloads, queries, or documents.
4. Validation — state checks performed, important risks, caveats, or unresolved questions.
5. Next steps — list concrete follow-up actions, or write None if nothing remains.

Rules:

• Do not omit a section; write None when a section does not apply.
• If files are produced, list each file path under Artifacts before its contents.
• If commands, JSON, SQL, YAML, or code are produced, put each artifact in fenced code blocks with the correct language tag when possible.
• Keep section names exactly as written above so output stays predictable across skills.

Workflow

1. Identify what you need

Translate the natural language query into concrete requirements:

• Who: specific authors, or any author?
• What kind: notes (1), reactions (7), reposts (6), zaps (9735), profiles (0)?
• Related to what: specific events (#e), specific people (#p), specific addressable events (#a)?
• When: time-bounded or open-ended?
• How many: limited initial fetch or ongoing subscription?

2. Determine AND vs OR

Ask: "Can a single event satisfy ALL my conditions simultaneously?"

• Yes -> one filter with all conditions (AND)
• No -> multiple filters (OR)

The most common mistake is cramming OR-logic into a single filter. If you need "events by Alice OR events mentioning Alice," that requires two filters.

3. Construct the filter(s)

Build each filter object. For each condition, add the appropriate field. Cross-reference with references/filter-patterns.md for common patterns.

4. Validate

Check each filter against these rules:

• All hex values are exactly 64 characters, lowercase
• Tag filter keys are single letters (#e, not #event)
• No NOT/exclusion logic (Nostr filters can't do this)
• since and until are unix timestamps in seconds (not milliseconds)
• limit is only used for initial queries, not ongoing subscriptions
• AND/OR semantics match the intent

5. Format as REQ

Wrap in the REQ message format:

["REQ", "<subscription-id>", <filter1>, <filter2>, ...]

Examples

Example 1: Get a full thread (root + all replies)

Need: The root event itself, plus all kind-1 replies that tag it.

A single filter can't do this because the root event won't have an #e tag pointing to itself. Use two filters (OR):

[
  "REQ",
  "thread-sub",
  { "ids": ["aabb...64chars"] },
  { "kinds": [1], "#e": ["aabb...64chars"] }
]

Filter 1 fetches the root by ID. Filter 2 fetches all kind-1 events that reference it via an e tag. Together (OR), you get the complete thread.

Why not one filter? {"ids": ["aabb..."], "#e": ["aabb..."]} would match only events whose own ID is aabb... AND that also tag aabb... -- which is almost certainly nothing.

Example 2: User's social feed

Need: A user's notes, reposts, and reactions.

All three share the same author, so one filter with multiple kinds works (AND on author, list-match on kinds):

{ "authors": ["<pubkey>"], "kinds": [1, 6, 7], "limit": 50 }

This works because kinds is a list -- the event matches if its kind is ANY of the listed values. Combined with authors (AND), this gives "events by this author that are notes OR reposts OR reactions."

Example 3: All engagement on an event

Need: Replies, reactions, zaps, and reposts of a specific event.

All engagement types tag the event via #e, but have different kinds. One filter works:

{ "#e": ["<event-id>"], "kinds": [1, 6, 7, 9735] }

Example 4: Events by author OR mentioning author

Need: Show everything relevant to a user -- their own posts and posts that mention them.

This requires OR (two filters), because an event can't simultaneously be authored by someone AND mention them in a p tag (well, it could, but you'd miss events that only satisfy one condition):

[
  "REQ",
  "user-activity",
  { "authors": ["<pk>"], "kinds": [1] },
  { "#p": ["<pk>"], "kinds": [1] }
]

Common Mistakes

Mistake	Why it's wrong	Fix
OR logic in one filter	{"authors": ["A"], "#p": ["A"]} means events BY A that ALSO tag A (AND)	Use two separate filters
#event or #pubkey as tag filter key	Tag filter keys are single letters only	Use #e, #p, #a, etc.
Non-hex values in ids, authors, #e, #p	Must be exact 64-char lowercase hex	Convert npub/note to hex first
Timestamps in milliseconds	Nostr uses seconds since epoch	Divide JS Date.now() by 1000
Using limit for ongoing subscriptions	limit only applies to the initial query batch	Remove limit for live subscriptions
Expecting NOT/exclusion	Nostr filters have no negation	Filter client-side after receiving events
Assuming tag filter matches all tag values	Only index 0 (the first value) is matched	Don't try to filter by relay hints or markers
Mixing replaceable event semantics	Relay returns only latest for kind 0, 3, 10000-19999	Don't expect historical versions

Quick Reference

Query	Filter
User's notes	{"authors": ["<pk>"], "kinds": [1]}
User's profile	{"authors": ["<pk>"], "kinds": [0]}
User's contacts	{"authors": ["<pk>"], "kinds": [3]}
User's relay list	{"authors": ["<pk>"], "kinds": [10002]}
Replies to event	{"kinds": [1], "#e": ["<eid>"]}
Reactions to event	{"kinds": [7], "#e": ["<eid>"]}
Zaps on event	{"kinds": [9735], "#e": ["<eid>"]}
Reposts of event	{"kinds": [6], "#e": ["<eid>"]}
Full thread	{"ids": ["<root>"]} + {"kinds": [1], "#e": ["<root>"]}
Comments on content	{"kinds": [1111], "#E": ["<root-id>"]}
User's DM relay list	{"authors": ["<pk>"], "kinds": [10050]}
All engagement on event	{"#e": ["<eid>"], "kinds": [1, 6, 7, 9735]}
Events mentioning user	{"#p": ["<pk>"]}
User's feed (notes+reposts+reactions)	{"authors": ["<pk>"], "kinds": [1, 6, 7]}

See references/filter-patterns.md for the full cookbook with advanced patterns and explanations.

Key Principles

1. AND within, OR between -- This is the single most important rule. Every condition in one filter is AND'd. Multiple filters are OR'd. There is no other way to combine conditions.

2. Hex or nothing -- ids, authors, #e, and #p values must be exact 64-character lowercase hex strings. No npub, note1, nprofile, or other NIP-19 encodings. Convert first.

3. Tag filters are shallow -- #e matches only the first value (index 0) of e tags. You cannot filter by relay hints, markers, or other positional tag values. Those must be filtered client-side.

4. No negation -- You cannot exclude events matching a condition. If you need "all kind-1 events except from author X," fetch all kind-1 events and filter client-side.

5. Limit is a suggestion for initial load -- limit tells the relay how many events to return in the initial batch (newest first). It does NOT cap an ongoing subscription. Relays may return fewer than requested.